<!doctype html><html lang="en">
 <head>
  <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
  <meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport">
  <title>P2993R3: Extend &lt;code>&lt;bit>&lt;/code> header function with overloads for &lt;code>std::simd&lt;/code></title>
<style data-fill-with="stylesheet">/******************************************************************************
 *                   Style sheet for the W3C specifications                   *
 *
 * Special classes handled by this style sheet include:
 *
 * Indices
 *   - .toc for the Table of Contents (<ol class="toc">)
 *     + <span class="secno"> for the section numbers
 *   - #toc for the Table of Contents (<nav id="toc">)
 *   - ul.index for Indices (<a href="#ref">term</a><span>, in § N.M</span>)
 *   - table.index for Index Tables (e.g. for properties or elements)
 *
 * Structural Markup
 *   - table.data for general data tables
 *     -> use 'scope' attribute, <colgroup>, <thead>, and <tbody> for best results !
 *     -> use <table class='complex data'> for extra-complex tables
 *     -> use <td class='long'> for paragraph-length cell content
 *     -> use <td class='pre'> when manual line breaks/indentation would help readability
 *   - dl.switch for switch statements
 *   - ol.algorithm for algorithms (helps to visualize nesting)
 *   - .figure and .caption (HTML4) and figure and figcaption (HTML5)
 *     -> .sidefigure for right-floated figures
 *   - ins/del
 *     -> ins/del.c### for candidate and proposed changes (amendments)
 *
 * Code
 *   - pre and code
 *
 * Special Sections
 *   - .note       for informative notes             (div, p, span, aside, details)
 *   - .example    for informative examples          (div, p, pre, span)
 *   - .issue      for issues                        (div, p, span)
 *   - .advisement for loud normative statements     (div, p, strong)
 *   - .annoying-warning for spec obsoletion notices (div, aside, details)
 *   - .correction for "candidate corrections"       (div, aside, details, section)
 *   - .addition   for "candidate additions"         (div, aside, details, section)
 *   - .correction.proposed for "proposed corrections" (div, aside, details, section)
 *   - .addition.proposed   for "proposed additions"   (div, aside, details, section)
 *
 * Definition Boxes
 *   - pre.def   for WebIDL definitions
 *   - table.def for tables that define other entities (e.g. CSS properties)
 *   - dl.def    for definition lists that define other entitles (e.g. HTML elements)
 *
 * Numbering
 *   - .secno for section numbers in .toc and headings (<span class='secno'>3.2</span>)
 *   - .marker for source-inserted example/figure/issue numbers (<span class='marker'>Issue 4</span>)
 *   - ::before styled for CSS-generated issue/example/figure numbers:
 *     -> Documents wishing to use this only need to add
 *        figcaption::before,
 *        .caption::before { content: "Figure "  counter(figure) " ";  }
 *        .example::before { content: "Example " counter(example) " "; }
 *        .issue::before   { content: "Issue "   counter(issue) " ";   }
 *
 * Header Stuff (ignore, just don't conflict with these classes)
 *   - .head for the header
 *   - .copyright for the copyright
 *
 * Outdated warning for old specs
 *
 * Miscellaneous
 *   - .overlarge for things that should be as wide as possible, even if
 *     that overflows the body text area. This can be used on an item or
 *     on its container, depending on the effect desired.
 *     Note that this styling basically doesn't help at all when printing,
 *     since A4 paper isn't much wider than the max-width here.
 *     It's better to design things to fit into a narrower measure if possible.
 *
 *   - js-added ToC jump links (see fixup.js)
 *
 ******************************************************************************/

/* color variables included separately for reliability */

/******************************************************************************/
/*                                    Body                                    */
/******************************************************************************/

	html {
	}

	body {
		counter-reset: example figure issue;

		/* Layout */
		max-width: 50em;			  /* limit line length to 50em for readability   */
		margin: 0 auto;				/* center text within page                    */
		padding: 1.6em 1.5em 2em 50px; /* assume 16px font size for downlevel clients */
		padding: 1.6em 1.5em 2em calc(26px + 1.5em); /* leave space for status flag    */

		/* Typography */
		line-height: 1.5;
		font-family: sans-serif;
		widows: 2;
		orphans: 2;
		word-wrap: break-word;
		overflow-wrap: break-word;
		hyphens: auto;

		color: black;
		color: var(--text);
		background: white top left fixed no-repeat;
		background: var(--bg) top left fixed no-repeat;
		background-size: 25px auto;
	}


/******************************************************************************/
/*                         Front Matter & Navigation                          */
/******************************************************************************/

/** Header ********************************************************************/

	div.head { margin-bottom: 1em; }
	div.head hr { border-style: solid; }

	div.head h1 {
		font-weight: bold;
		margin: 0 0 .1em;
		font-size: 220%;
	}

	div.head h2 { margin-bottom: 1.5em;}

/** W3C Logo ******************************************************************/

	.head .logo {
		float: right;
		margin: 0.4rem 0 0.2rem .4rem;
	}

	.head img[src*="logos/W3C"] {
		display: block;
		border: solid #1a5e9a;
		border: solid var(--logo-bg);
		border-width: .65rem .7rem .6rem;
		border-radius: .4rem;
		background: #1a5e9a;
		background: var(--logo-bg);
		color: white;
		color: var(--logo-text);
		font-weight: bold;
	}

	.head a:hover > img[src*="logos/W3C"],
	.head a:focus > img[src*="logos/W3C"] {
		opacity: .8;
	}

	.head a:active > img[src*="logos/W3C"] {
		background: #c00;
		background: var(--logo-active-bg);
		border-color: #c00;
		border-color: var(--logo-active-bg);
	}

	/* see also additional rules in Link Styling section */

/** Copyright *****************************************************************/

	p.copyright,
	p.copyright small { font-size: small; }

/** Back to Top / ToC Toggle **************************************************/

	@media print {
		#toc-nav {
			display: none;
		}
	}
	@media not print {
		#toc-nav {
			position: fixed;
			z-index: 3;
			bottom: 0; left: 0;
			margin: 0;
			min-width: 1.33em;
			border-top-right-radius: 2rem;
			box-shadow: 0 0 2px;
			font-size: 1.5em;
		}
		#toc-nav > a {
			display: block;
			white-space: nowrap;

			height: 1.33em;
			padding: .1em 0.3em;
			margin: 0;

			box-shadow: 0 0 2px;
			border: none;
			border-top-right-radius: 1.33em;

			color: #707070;
			color: var(--tocnav-normal-text);
			background: white;
			background: var(--tocnav-normal-bg);
		}
		#toc-nav > a:hover,
		#toc-nav > a:focus {
			color: black;
			color: var(--tocnav-hover-text);
			background: #f8f8f8;
			background: var(--tocnav-hover-bg);
		}
		#toc-nav > a:active {
			color: #c00;
			color: var(--tocnav-active-text);
			background: white;
			background: var(--tocnav-active-bg);
		}

		#toc-nav > #toc-jump {
			padding-bottom: 2em;
			margin-bottom: -1.9em;
		}

		/* statusbar gets in the way on keyboard focus; remove once browsers fix */
		#toc-nav > a[href="#toc"]:not(:hover):focus:last-child {
			padding-bottom: 1.5rem;
		}

		#toc-nav:not(:hover) > a:not(:focus) > span + span {
			/* Ideally this uses :focus-within on #toc-nav */
			display: none;
		}
		#toc-nav > a > span + span {
			padding-right: 0.2em;
		}
	}

/** ToC Sidebar ***************************************************************/

	/* Floating sidebar */
	@media screen {
		body.toc-sidebar #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			max-width: 80%;
			max-width: calc(100% - 2em - 26px);
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			color: black;
			color: var(--tocsidebar-text);
			background: inherit;
			background-color: #f7f8f9;
			background-color: var(--tocsidebar-bg);
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
			box-shadow: -.1em 0 .25em var(--tocsidebar-shadow) inset;
		}
		body.toc-sidebar #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
			color: var(--tocsidebar-heading-text);
		}
		body.toc-sidebar #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	/* Hide main scroller when only the ToC is visible anyway */
	@media screen and (max-width: 28em) {
		body.toc-sidebar {
			overflow: hidden;
		}
	}

	/* Sidebar with its own space */
	@media screen and (min-width: 78em) {
		body:not(.toc-inline) #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			color: black;
			color: var(--tocsidebar-text);
			background: inherit;
			background-color: #f7f8f9;
			background-color: var(--tocsidebar-bg);
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
			box-shadow: -.1em 0 .25em var(--tocsidebar-shadow) inset;
		}
		body:not(.toc-inline) #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
			color: var(--tocsidebar-heading-text);
		}

		body:not(.toc-inline) {
			padding-left: 29em;
		}
		/* See also Overflow section at the bottom */

		body:not(.toc-inline) #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	@media screen and (min-width: 90em) {
		body:not(.toc-inline) {
			margin: 0 4em;
		}
	}

/******************************************************************************/
/*                                Sectioning                                  */
/******************************************************************************/

/** Headings ******************************************************************/

	h1, h2, h3, h4, h5, h6, dt {
		page-break-after: avoid;
		page-break-inside: avoid;
		font: 100% sans-serif;   /* Reset all font styling to clear out UA styles */
		font-family: inherit;	/* Inherit the font family. */
		line-height: 1.2;		/* Keep wrapped headings compact */
		hyphens: manual;		/* Hyphenated headings look weird */
	}

	h2, h3, h4, h5, h6 {
		margin-top: 3rem;
	}

	h1, h2, h3 {
		color: #005A9C;
		color: var(--heading-text);
	}

	h1 { font-size: 170%; }
	h2 { font-size: 140%; }
	h3 { font-size: 120%; }
	h4 { font-weight: bold; }
	h5 { font-style: italic; }
	h6 { font-variant: small-caps; }
	dt { font-weight: bold; }

/** Subheadings ***************************************************************/

	h1 + h2,
	#profile-and-date {
		/* #profile-and-date is a subtitle in an H2 under the H1 */
		margin-top: 0;
	}
	h2 + h3,
	h3 + h4,
	h4 + h5,
	h5 + h6 {
		margin-top: 1.2em; /* = 1 x line-height */
	}

/** Section divider ***********************************************************/

	:not(.head) > :not(.head) + hr {
		font-size: 1.5em;
		text-align: center;
		margin: 1em auto;
		height: auto;
		color: black;
		color: var(--hr-text);
		border: transparent solid 0;
		background: transparent;
	}
	:not(.head) > hr::before {
		content: "\2727\2003\2003\2727\2003\2003\2727";
	}

/******************************************************************************/
/*                            Paragraphs and Lists                            */
/******************************************************************************/

	p {
		margin: 1em 0;
	}

	dd > p:first-child,
	li > p:first-child {
		margin-top: 0;
	}

	ul, ol {
		margin-left: 0;
		padding-left: 2em;
	}

	li {
		margin: 0.25em 0 0.5em;
		padding: 0;
	}

	dl dd {
		margin: 0 0 .5em 2em;
	}

	.head dd + dd { /* compact for header */
		margin-top: -.5em;
	}

	/* Style for algorithms */
	ol.algorithm ol:not(.algorithm),
	.algorithm > ol ol:not(.algorithm) {
	border-left: 0.5em solid #DEF;
	border-left: 0.5em solid var(--algo-border);
	}

	/* Put nice boxes around each algorithm. */
	[data-algorithm]:not(.heading) {
	 padding: .5em;
	 border: thin solid #ddd;
	 border: thin solid var(--algo-border);
	 border-radius: .5em;
	 margin: .5em calc(-0.5em - 1px);
	}
	[data-algorithm]:not(.heading) > :first-child {
	 margin-top: 0;
	}
	[data-algorithm]:not(.heading) > :last-child {
	 margin-bottom: 0;
	}

	/* Style for switch/case <dl>s */
	dl.switch > dd > ol.only,
	dl.switch > dd > .only > ol {
	margin-left: 0;
	}
	dl.switch > dd > ol.algorithm,
	dl.switch > dd > .algorithm > ol {
	margin-left: -2em;
	}
	dl.switch {
	padding-left: 2em;
	}
	dl.switch > dt {
	text-indent: -1.5em;
	margin-top: 1em;
	}
	dl.switch > dt + dt {
	margin-top: 0;
	}
	dl.switch > dt::before {
	content: '\21AA';
	padding: 0 0.5em 0 0;
	display: inline-block;
	width: 1em;
	text-align: right;
	line-height: 0.5em;
	}

/** Terminology Markup ********************************************************/


/******************************************************************************/
/*                                 Inline Markup                              */
/******************************************************************************/

/** Terminology Markup ********************************************************/
	dfn   { /* Defining instance */
		font-weight: bolder;
	}
	a > i { /* Instance of term */
		font-style: normal;
	}
	dt dfn code, code.idl {
		font-size: inherit;
	}
	dfn var {
		font-style: normal;
	}

/** Change Marking ************************************************************/

	del {
		color: #aa0000;
		color: var(--del-text);
		background: transparent;
		background: var(--del-bg);
		text-decoration: line-through;
	}
	ins {
		color: #006100;
		color: var(--ins-text);
		background: transparent;
		background: var(--ins-bg);
		text-decoration: underline;
	}

	/* for amendments (candidate/proposed changes) */

	.amendment ins, .correction ins, .addition ins,
	ins[class^=c] {
		text-decoration-style: dotted;
	}
	.amendment del, .correction del, .addition del,
	del[class^=c] {
		text-decoration-style: dotted;
	}
	.amendment.proposed ins, .correction.proposed ins, .addition.proposed ins,
	ins[class^=c].proposed {
		text-decoration-style: double;
	}
	.amendment.proposed del, .correction.proposed del, .addition.proposed del,
	del[class^=c].proposed {
		text-decoration-style: double;
	}

/** Miscellaneous improvements to inline formatting ***************************/

	sup {
		vertical-align: super;
		font-size: 80%
	}

/******************************************************************************/
/*                                    Code                                    */
/******************************************************************************/

/** General monospace/pre rules ***********************************************/

	pre, code, samp {
		font-family: Menlo, Consolas, "DejaVu Sans Mono", Monaco, monospace;
		font-size: .9em;
		hyphens: none;
		text-transform: none;
		text-align: left;
		text-align: start;
		font-variant: normal;
		orphans: 3;
		widows: 3;
		page-break-before: avoid;
	}
	pre code,
	code code {
		font-size: 100%;
	}

	pre {
		margin-top: 1em;
		margin-bottom: 1em;
		overflow: auto;
	}

/** Inline Code fragments *****************************************************/

	/* Do something nice. */

/******************************************************************************/
/*                                    Links                                   */
/******************************************************************************/

/** General Hyperlinks ********************************************************/

	/* We hyperlink a lot, so make it less intrusive */
	a[href] {
		color: #034575;
		color: var(--a-normal-text);
		text-decoration: underline #707070;
		text-decoration: underline var(--a-normal-underline);
		text-decoration-skip-ink: none;
	}
	a:visited {
		color: #034575;
		color: var(--a-visited-text);
		text-decoration-color: #bbb;
		text-decoration-color: var(--a-visited-underline);
	}

	/* Indicate interaction with the link */
	a[href]:focus,
	a[href]:hover {
		text-decoration-thickness: 2px;
	}
	a[href]:active {
		color: #c00;
		color: var(--a-active-text);
		text-decoration-color: #c00;
		text-decoration-color: var(--a-active-underline);
	}

	/* Backout above styling for W3C logo */
	.head .logo,
	.head .logo a {
		border: none;
		text-decoration: none;
		background: transparent;
	}

/******************************************************************************/
/*                                    Images                                  */
/******************************************************************************/

	img {
		border-style: none;
	}

	img, svg {
		/* Intentionally not color-scheme aware. */
		background: white;
	}

	/* For autogen numbers, add
	  .caption::before, figcaption::before { content: "Figure " counter(figure) ". "; }
	*/

	figure, .figure, .sidefigure {
		page-break-inside: avoid;
		text-align: center;
		margin: 2.5em 0;
	}
	.figure img,	.sidefigure img,	figure img,
	.figure object, .sidefigure object, figure object {
		max-width: 100%;
		margin: auto;
		height: auto;
	}
	.figure pre, .sidefigure pre, figure pre {
		text-align: left;
		display: table;
		margin: 1em auto;
	}
	.figure table, figure table {
		margin: auto;
	}
	@media screen and (min-width: 20em) {
		.sidefigure {
			float: right;
			width: 50%;
			margin: 0 0 0.5em 0.5em;
		}
	}
	.caption, figcaption, caption {
		font-style: italic;
		font-size: 90%;
	}
	.caption::before, figcaption::before, figcaption > .marker {
		font-weight: bold;
	}
	.caption, figcaption {
		counter-increment: figure;
	}

	/* DL list is indented 2em, but figure inside it is not */
	dd > .figure, dd > figure { margin-left: -2em; }

/******************************************************************************/
/*                             Colored Boxes                                  */
/******************************************************************************/

	.issue, .note, .example, .assertion, .advisement, blockquote,
	.amendment, .correction, .addition {
		margin: 1em auto;
		padding: .5em;
		border: .5em;
		border-left-style: solid;
		page-break-inside: avoid;
	}
	span.issue, span.note {
		padding: .1em .5em .15em;
		border-right-style: solid;
	}

	blockquote > :first-child,
	.note  > p:first-child,
	.issue > p:first-child,
	.amendment > p:first-child,
	.correction > p:first-child,
	.addition > p:first-child {
		margin-top: 0;
	}
	blockquote > :last-child,
	.note  > p:last-child,
	.issue > p:last-child,
	.amendment > p:last-child,
	.correction > p:last-child,
	.addition > p:last-child {
		margin-bottom: 0;
	}


	.issue::before, .issue > .marker,
	.example::before, .example > .marker,
	.note::before, .note > .marker,
	details.note > summary > .marker,
	.amendment::before, .amendment > .marker,
	details.amendment > summary > .marker,
	.addition::before, .addition > .marker,
	addition.amendment > summary > .marker,
	.correction::before, .correction > .marker,
	correction.amendment > summary > .marker
	{
		text-transform: uppercase;
		padding-right: 1em;
	}

	.example::before, .example > .marker {
		display: block;
		padding-right: 0em;
	}

/** Blockquotes ***************************************************************/

	blockquote {
		border-color: silver;
		border-color: var(--blockquote-border);
		background: transparent;
		background: var(--blockquote-bg);
		color: currentcolor;
		color: var(--blockquote-text);
	}

/** Open issue ****************************************************************/

	.issue {
		border-color: #e05252;
		border-color: var(--issue-border);
		background: #fbe9e9;
		background: var(--issue-bg);
		color: black;
		color: var(--issue-text);
		counter-increment: issue;
		overflow: auto;
	}
	.issue::before, .issue > .marker {
		color: #831616;
		color: var(--issueheading-text);
	}
	/* Add .issue::before { content: "Issue " counter(issue) " "; } for autogen numbers,
	  or use class="marker" to mark up the issue number in source. */

/** Example *******************************************************************/

	.example {
		border-color: #e0cb52;
		border-color: var(--example-border);
		background: #fcfaee;
		background: var(--example-bg);
		color: black;
		color: var(--example-text);
		counter-increment: example;
		overflow: auto;
		clear: both;
	}
	.example::before, .example > .marker {
		color: #574b0f;
		color: var(--exampleheading-text);
	}
	/* Add .example::before { content: "Example " counter(example) " "; } for autogen numbers,
	  or use class="marker" to mark up the example number in source. */

/** Non-normative Note ********************************************************/

	.note {
		border-color: #52e052;
		border-color: var(--note-border);
		background: #e9fbe9;
		background: var(--note-bg);
		color: black;
		color: var(--note-text);
		overflow: auto;
	}

	.note::before, .note > .marker,
	details.note > summary {
		color: hsl(120, 70%, 30%);
		color: var(--noteheading-text);
	}
	/* Add .note::before { content: "Note "; } for autogen label,
	  or use class="marker" to mark up the label in source. */

	details.note[open] > summary {
		border-bottom: 1px silver solid;
		border-bottom: 1px var(--notesummary-underline) solid;
	}

/** Assertion Box *************************************************************/
	/*  for assertions in algorithms */

	.assertion {
		border-color: #AAA;
		border-color: var(--assertion-border);
		background: #EEE;
		background: var(--assertion-bg);
		color: black;
		color: var(--assertion-text);
	}

/** Advisement Box ************************************************************/
	/*  for attention-grabbing normative statements */

	.advisement {
		border-color: orange;
		border-color: var(--advisement-border);
		border-style: none solid;
		background: #fec;
		background: var(--advisement-bg);
		color: black;
		color: var(--advisement-text);
	}
	strong.advisement {
		display: block;
		text-align: center;
	}
	.advisement::before, .advisement > .marker {
		color: #b35f00;
		color: var(--advisementheading-text);
	}

/** Amendment Box *************************************************************/

	.amendment, .correction, .addition {
		border-color: #330099;
		border-color: var(--amendment-border);
		background: #F5F0FF;
		background: var(--amendment-bg);
		color: black;
		color: var(--amendment-text);
	}
	.amendment.proposed, .correction.proposed, .addition.proposed {
		border-style: solid;
		border-block-width: 0.25em;
	}
	.amendment::before, .amendment > .marker,
	details.amendment > summary::before, details.amendment > summary > .marker,
	.correction::before, .correction > .marker,
	details.correction > summary::before, details.correction > summary > .marker,
	.addition::before, .addition > .marker,
	details.addition > summary::before, details.addition > summary > .marker {
		color: #220066;
		color: var(--amendmentheading-text);
	}
	.amendment.proposed::before, .amendment.proposed > .marker,
	details.amendment.proposed > summary::before, details.amendment.proposed > summary > .marker,
	.correction.proposed::before, .correction.proposed > .marker,
	details.correction.proposed > summary::before, details.correction.proposed > summary > .marker,
	.addition.proposed::before, .addition.proposed > .marker,
	details.addition.proposed > summary::before, details.addition.proposed > summary > .marker {
		font-weight: bold;
	}

/** Spec Obsoletion Notice ****************************************************/
	/* obnoxious obsoletion notice for older/abandoned specs. */

	details {
		display: block;
	}
	summary {
		font-weight: bolder;
	}

	.annoying-warning:not(details),
	details.annoying-warning:not([open]) > summary,
	details.annoying-warning[open] {
		background: hsla(40,100%,50%,0.95);
		background: var(--warning-bg);
		color: black;
		color: var(--warning-text);
		padding: .75em 1em;
		border: red;
		border: var(--warning-border);
		border-style: solid none;
		box-shadow: 0 2px 8px black;
		text-align: center;
	}
	.annoying-warning :last-child {
		margin-bottom: 0;
	}

@media not print {
	details.annoying-warning[open] {
		position: fixed;
		left: 0;
		right: 0;
		bottom: 2em;
		z-index: 1000;
	}
}

	details.annoying-warning:not([open]) > summary {
		text-align: center;
	}

/** Entity Definition Boxes ***************************************************/

	.def {
		padding: .5em 1em;
		background: #def;
		background: var(--def-bg);
		margin: 1.2em 0;
		border-left: 0.5em solid #8ccbf2;
		border-left: 0.5em solid var(--def-border);
		color: black;
		color: var(--def-text);
	}

/******************************************************************************/
/*                                    Tables                                  */
/******************************************************************************/

	th, td {
		text-align: left;
		text-align: start;
	}

/** Property/Descriptor Definition Tables *************************************/

	table.def {
		/* inherits .def box styling, see above */
		width: 100%;
		border-spacing: 0;
	}

	table.def td,
	table.def th {
		padding: 0.5em;
		vertical-align: baseline;
		border-bottom: 1px solid #bbd7e9;
		border-bottom: 1px solid var(--defrow-border);
	}

	table.def > tbody > tr:last-child th,
	table.def > tbody > tr:last-child td {
		border-bottom: 0;
	}

	table.def th {
		font-style: italic;
		font-weight: normal;
		padding-left: 1em;
		width: 3em;
	}

	/* For when values are extra-complex and need formatting for readability */
	table td.pre {
		white-space: pre-wrap;
	}

	/* A footnote at the bottom of a def table */
	table.def td.footnote {
		padding-top: 0.6em;
	}
	table.def td.footnote::before {
		content: " ";
		display: block;
		height: 0.6em;
		width: 4em;
		border-top: thin solid;
	}

/** Data tables (and properly marked-up index tables) *************************/
	/*
		<table class="data"> highlights structural relationships in a table
		when correct markup is used (e.g. thead/tbody, th vs. td, scope attribute)

		Use class="complex data" for particularly complicated tables --
		(This will draw more lines: busier, but clearer.)

		Use class="long" on table cells with paragraph-like contents
		(This will adjust text alignment accordingly.)
		Alternately use class="longlastcol" on tables, to have the last column assume "long".
	*/

	table {
		word-wrap: normal;
		overflow-wrap: normal;
		hyphens: manual;
	}

	table.data,
	table.index {
		margin: 1em auto;
		border-collapse: collapse;
		border: hidden;
		width: 100%;
	}
	table.data caption,
	table.index caption {
		max-width: 50em;
		margin: 0 auto 1em;
	}

	table.data td,  table.data th,
	table.index td, table.index th {
		padding: 0.5em 1em;
		border-width: 1px;
		border-color: silver;
		border-color: var(--datacell-border);
		border-top-style: solid;
	}

	table.data thead td:empty {
		padding: 0;
		border: 0;
	}

	table.data  thead,
	table.index thead,
	table.data  tbody,
	table.index tbody {
		border-bottom: 2px solid;
	}

	table.data colgroup,
	table.index colgroup {
		border-left: 2px solid;
	}

	table.data  tbody th:first-child,
	table.index tbody th:first-child  {
		border-right: 2px solid;
		border-top: 1px solid silver;
		border-top: 1px solid var(--datacell-border);
		padding-right: 1em;
	}

	table.data th[colspan],
	table.data td[colspan] {
		text-align: center;
	}

	table.complex.data th,
	table.complex.data td {
		border: 1px solid silver;
		border: 1px solid var(--datacell-border);
		text-align: center;
	}

	table.data.longlastcol td:last-child,
	table.data td.long {
		vertical-align: baseline;
		text-align: left;
	}

	table.data img {
		vertical-align: middle;
	}


/*
Alternate table alignment rules

	table.data,
	table.index {
		text-align: center;
	}

	table.data  thead th[scope="row"],
	table.index thead th[scope="row"] {
		text-align: right;
	}

	table.data  tbody th:first-child,
	table.index tbody th:first-child  {
		text-align: right;
	}

Possible extra rowspan handling

	table.data  tbody th[rowspan]:not([rowspan='1']),
	table.index tbody th[rowspan]:not([rowspan='1']),
	table.data  tbody td[rowspan]:not([rowspan='1']),
	table.index tbody td[rowspan]:not([rowspan='1']) {
		border-left: 1px solid silver;
	}

	table.data  tbody th[rowspan]:first-child,
	table.index tbody th[rowspan]:first-child,
	table.data  tbody td[rowspan]:first-child,
	table.index tbody td[rowspan]:first-child{
		border-left: 0;
		border-right: 1px solid silver;
	}
*/

/******************************************************************************/
/*                                  Indices                                   */
/******************************************************************************/


/** Table of Contents *********************************************************/

	.toc a {
		/* More spacing; use padding to make it part of the click target. */
		padding: 0.1rem 1px 0;
		/* Larger, more consistently-sized click target */
		display: block;
		/* Switch to using border-bottom for underlines */
		text-decoration: none;
		border-bottom: 1px solid;
		/* Reverse color scheme */
		color: black;
		color: var(--toclink-text);
		border-color: #3980b5;
		border-color: var(--toclink-underline);
	}
	.toc a:visited {
		color: black;
		color: var(--toclink-visited-text);
		border-color: #054572;
		border-color: var(--toclink-visited-underline);
	}
	.toc a:focus,
	.toc a:hover {
		background: rgba(75%, 75%, 75%, .25);
		background: var(--a-hover-bg);
		border-bottom-width: 3px;
		margin-bottom: -2px;
	}
	.toc a:not(:focus):not(:hover) {
		/* Allow colors to cascade through from link styling */
		border-bottom-color: transparent;
	}

	.toc, .toc ol, .toc ul, .toc li {
		list-style: none; /* Numbers must be inlined into source */
		/* because generated content isn't search/selectable and markers can't do multilevel yet */
		margin:  0;
		padding: 0;
	}
	.toc {
		line-height: 1.1em;
	}

	/* ToC not indented until third level, but font style & margins show hierarchy */
	.toc > li			{ font-weight: bold;   }
	.toc > li li		 { font-weight: normal; }
	.toc > li li li	  { font-size:   95%;	}
	.toc > li li li li	{ font-size:   90%;	}
	.toc > li li li li li { font-size:   85%;	}

	/* @supports not (display:grid) { */
		.toc > li			{ margin: 1.5rem 0;	}
		.toc > li li		 { margin: 0.3rem 0;	}
		.toc > li li li	  { margin-left: 2rem;   }

		/* Section numbers in a column of their own */
		.toc .secno {
			float: left;
			width: 4rem;
			white-space: nowrap;
		}
		.toc > li li li li .secno { font-size: 85%; }
		.toc > li li li li li .secno { font-size: 100%; }

		.toc li {
			clear: both;
		}

		:not(li) > .toc			 { margin-left:  5rem; }
		.toc .secno				 { margin-left: -5rem; }
		.toc > li li li .secno	  { margin-left: -7rem; }
		.toc > li li li li .secno	{ margin-left: -9rem; }
		.toc > li li li li li .secno { margin-left: -11rem; }

		/* Tighten up indentation in narrow ToCs */
		@media (max-width: 30em) {
			:not(li) > .toc			 { margin-left:  4rem; }
			.toc .secno				 { margin-left: -4rem; }
			.toc > li li li			 { margin-left:  1rem; }
			.toc > li li li .secno	  { margin-left: -5rem; }
			.toc > li li li li .secno	{ margin-left: -6rem; }
			.toc > li li li li li .secno { margin-left: -7rem; }
		}
		/* Loosen it on wide screens */
		@media screen and (min-width: 78em) {
			body:not(.toc-inline) :not(li) > .toc			 { margin-left:  4rem; }
			body:not(.toc-inline) .toc .secno				 { margin-left: -4rem; }
			body:not(.toc-inline) .toc > li li li			 { margin-left:  1rem; }
			body:not(.toc-inline) .toc > li li li .secno	  { margin-left: -5rem; }
			body:not(.toc-inline) .toc > li li li li .secno	{ margin-left: -6rem; }
			body:not(.toc-inline) .toc > li li li li li .secno { margin-left: -7rem; }
	}
	/* } */

	@supports (display:grid) and (display:contents) {
		/* Use #toc over .toc to override non-@supports rules. */
		#toc {
			display: grid;
			align-content: start;
			grid-template-columns: auto 1fr;
			grid-column-gap: 1rem;
			column-gap: 1rem;
			grid-row-gap: .6rem;
			row-gap: .6rem;
		}
		#toc h2 {
			grid-column: 1 / -1;
			margin-bottom: 0;
		}
		#toc ol,
		#toc li,
		#toc a {
			display: contents;
			/* Switch <a> to subgrid when supported */
		}
		#toc span {
			margin: 0;
		}
		#toc > .toc > li > a > span {
			/* The spans of the top-level list,
			  comprising the first items of each top-level section. */
			margin-top: 1.1rem;
		}
		#toc#toc .secno { /* Ugh, need more specificity to override base.css */
			grid-column: 1;
			width: auto;
			margin-left: 0;
		}
		#toc .content {
			grid-column: 2;
			width: auto;
			margin-right: 1rem;
			border-bottom: 3px solid transparent;
			margin-bottom: -3px;
		}
		#toc .content:hover,
		#toc .content:focus {
			background: rgba(75%, 75%, 75%, .25);
			background: var(--a-hover-bg);
			border-bottom-color: #054572;
			border-bottom-color: var(--toclink-underline);
		}
		#toc li li li .content {
			margin-left: 1rem;
		}
		#toc li li li li .content {
			margin-left: 2rem;
		}
	}


/** Index *********************************************************************/

	/* Index Lists: Layout */
	ul.index	  { margin-left: 0; columns: 15em; text-indent: 1em hanging; }
	ul.index li	{ margin-left: 0; list-style: none; break-inside: avoid; }
	ul.index li li { margin-left: 1em; }
	ul.index dl	{ margin-top: 0; }
	ul.index dt	{ margin: .2em 0 .2em 20px;}
	ul.index dd	{ margin: .2em 0 .2em 40px;}
	/* Index Lists: Typography */
	ul.index ul,
	ul.index dl { font-size: smaller; }
	@media not print {
		ul.index li a + span {
			white-space: nowrap;
			color: transparent; }
		ul.index li a:hover + span,
		ul.index li a:focus + span {
			color: #707070;
			color: var(--indexinfo-text);
		}
	}

/** Index Tables *****************************************************/
	/* See also the data table styling section, which this effectively subclasses */

	table.index {
		font-size: small;
		border-collapse: collapse;
		border-spacing: 0;
		text-align: left;
		margin: 1em 0;
	}

	table.index td,
	table.index th {
		padding: 0.4em;
	}

	table.index tr:hover td:not([rowspan]),
	table.index tr:hover th:not([rowspan]) {
		color: black;
		color: var(--indextable-hover-text);
		background: #f7f8f9;
		background: var(--indextable-hover-bg);
	}

	/* The link in the first column in the property table (formerly a TD) */
	table.index th:first-child a {
		font-weight: bold;
	}

/** Outdated warning **********************************************************/

.outdated-spec {
	color: black;
	color: var(--outdatedspec-text);
	background-color: rgba(0,0,0,0.5);
	background-color: var(--outdatedspec-bg);
}

.outdated-warning {
	position: fixed;
	bottom: 50%;
	left: 0;
	right: 0;
	margin: 0 auto;
	width: 50%;
	background: maroon;
	background: var(--outdated-bg);
	color: white;
	color: var(--outdated-text);
	border-radius: 1em;
	box-shadow: 0 0 1em red;
	box-shadow: 0 0 1em var(--outdated-shadow);
	padding: 2em;
	text-align: center;
	z-index: 2;
}

.outdated-warning a {
	color: currentcolor;
	background: transparent;
}

.edited-rec-warning {
	background: darkorange;
	background: var(--editedrec-bg);
	box-shadow: 0 0 1em;
}

.outdated-warning button {
	color: var(--outdated-text);
	border-radius: 1em;
	box-shadow: 0 0 1em red;
	box-shadow: 0 0 1em var(--outdated-shadow);
	padding: 2em;
	text-align: center;
	z-index: 2;
}

.outdated-warning a {
	color: currentcolor;
	background: transparent;
}

.edited-rec-warning {
	background: darkorange;
	background: var(--editedrec-bg);
	box-shadow: 0 0 1em;
}

.outdated-warning button {
	position: absolute;
	top: 0;
	right:0;
	margin: 0;
	border: 0;
	padding: 0.25em 0.5em;
	background: transparent;
	color: white;
	color: var(--outdated-text);
	font:1em sans-serif;
	text-align:center;
}

.outdated-warning span {
	display: block;
}

.outdated-collapsed {
	bottom: 0;
	border-radius: 0;
	width: 100%;
	padding: 0;
}

/******************************************************************************/
/*                                    Print                                   */
/******************************************************************************/

	@media print {
		/* Pages have their own margins. */
		html {
			margin: 0;
		}
		/* Serif for print. */
		body {
			font-family: serif;
		}

		.outdated-warning {
			position: absolute;
			border-style: solid;
			border-color: red;
		}

		.outdated-warning input {
			display: none;
		}
	}
	@page {
		margin: 1.5cm 1.1cm;
	}



/******************************************************************************/
/*                             Overflow Control                               */
/******************************************************************************/

	.figure .caption, .sidefigure .caption, figcaption {
		/* in case figure is overlarge, limit caption to 50em */
		max-width: 50rem;
		margin-left: auto;
		margin-right: auto;
	}
	.overlarge {
		/* Magic to create good item positioning:
		  "content column" is 50ems wide at max; less on smaller screens.
		  Extra space (after ToC + content) is empty on the right.

		  1. When item < content column, centers item in column.
		  2. When content < item < available, left-aligns.
		  3. When item > available, fills available + scroll bar.
		*/
		display: grid;
		grid-template-columns: minmax(0, 50em);
	}
	.overlarge > table {
		/* limit preferred width of table */
		max-width: 50em;
		margin-left: auto;
		margin-right: auto;
	}

	@media (min-width: 55em) {
		.overlarge {
			margin-right: calc(13px + 26.5rem - 50vw);
			max-width: none;
		}
	}
	@media screen and (min-width: 78em) {
		body:not(.toc-inline) .overlarge {
			/* 30.5em body padding 50em content area */
			margin-right: calc(40em - 50vw) !important;
		}
	}
	@media screen and (min-width: 90em) {
		body:not(.toc-inline) .overlarge {
			/* 4em html margin 30.5em body padding 50em content area */
			margin-right: calc(84.5em - 100vw) !important;
		}
	}

	@media not print {
		.overlarge {
			overflow-x: auto;
			/* See Lea Verou's explanation background-attachment:
			* http://lea.verou.me/2012/04/background-attachment-local/
			*
			background: top left  / 4em 100% linear-gradient(to right,  #ffffff, rgba(255, 255, 255, 0)) local,
						top right / 4em 100% linear-gradient(to left, #ffffff, rgba(255, 255, 255, 0)) local,
						top left  / 1em 100% linear-gradient(to right,  #c3c3c5, rgba(195, 195, 197, 0)) scroll,
						top right / 1em 100% linear-gradient(to left, #c3c3c5, rgba(195, 195, 197, 0)) scroll,
						white;
			background-repeat: no-repeat;
			*/
		}
	}
</style>
<style>
    table, th, td {
      border: 1px solid black;
      border-collapse: collapse;
      vertical-align: top;
    }
    th, td {
      border-left: none;
      border-right: none;
      padding: 0px 10px;
    }
    th {
      text-align: center;
    }

    del { background: #fcc; color: #000; text-decoration: line-through; }
    ins { background: #cfc; color: #000; }
    blockquote .highlight:not(.idl) { background: initial; margin: initial; padding: 0.5em }
    blockquote ul { background: inherit; }
    blockquote code.highlight:not(.idl) { padding: initial; }
    blockquote c-[a] { color: inherit; } /* Keyword.Declaration */
    blockquote c-[b] { color: inherit; } /* Keyword.Type */
    blockquote c-[c] { color: inherit; } /* Comment */
    blockquote c-[d] { color: inherit; } /* Comment.Multiline */
    blockquote c-[e] { color: inherit; } /* Name.Attribute */
    blockquote c-[f] { color: inherit; } /* Name.Tag */
    blockquote c-[g] { color: inherit; } /* Name.Variable */
    blockquote c-[k] { color: inherit; } /* Keyword */
    blockquote c-[l] { color: inherit; } /* Literal */
    blockquote c-[m] { color: inherit; } /* Literal.Number */
    blockquote c-[n] { color: inherit; } /* Name */
    blockquote c-[o] { color: inherit; } /* Operator */
    blockquote c-[p] { color: inherit; } /* Punctuation */
    blockquote c-[s] { color: inherit; } /* Literal.String */
    blockquote c-[t] { color: inherit; } /* Literal.String.Single */
    blockquote c-[u] { color: inherit; } /* Literal.String.Double */
    blockquote c-[cp] { color: inherit; } /* Comment.Preproc */
    blockquote c-[c1] { color: inherit; } /* Comment.Single */
    blockquote c-[cs] { color: inherit; } /* Comment.Special */
    blockquote c-[kc] { color: inherit; } /* Keyword.Constant */
    blockquote c-[kn] { color: inherit; } /* Keyword.Namespace */
    blockquote c-[kp] { color: inherit; } /* Keyword.Pseudo */
    blockquote c-[kr] { color: inherit; } /* Keyword.Reserved */
    blockquote c-[ld] { color: inherit; } /* Literal.Date */
    blockquote c-[nc] { color: inherit; } /* Name.Class */
    blockquote c-[no] { color: inherit; } /* Name.Constant */
    blockquote c-[nd] { color: inherit; } /* Name.Decorator */
    blockquote c-[ni] { color: inherit; } /* Name.Entity */
    blockquote c-[ne] { color: inherit; } /* Name.Exception */
    blockquote c-[nf] { color: inherit; } /* Name.Function */
    blockquote c-[nl] { color: inherit; } /* Name.Label */
    blockquote c-[nn] { color: inherit; } /* Name.Namespace */
    blockquote c-[py] { color: inherit; } /* Name.Property */
    blockquote c-[ow] { color: inherit; } /* Operator.Word */
    blockquote c-[mb] { color: inherit; } /* Literal.Number.Bin */
    blockquote c-[mf] { color: inherit; } /* Literal.Number.Float */
    blockquote c-[mh] { color: inherit; } /* Literal.Number.Hex */
    blockquote c-[mi] { color: inherit; } /* Literal.Number.Integer */
    blockquote c-[mo] { color: inherit; } /* Literal.Number.Oct */
    blockquote c-[sb] { color: inherit; } /* Literal.String.Backtick */
    blockquote c-[sc] { color: inherit; } /* Literal.String.Char */
    blockquote c-[sd] { color: inherit; } /* Literal.String.Doc */
    blockquote c-[se] { color: inherit; } /* Literal.String.Escape */
    blockquote c-[sh] { color: inherit; } /* Literal.String.Heredoc */
    blockquote c-[si] { color: inherit; } /* Literal.String.Interpol */
    blockquote c-[sx] { color: inherit; } /* Literal.String.Other */
    blockquote c-[sr] { color: inherit; } /* Literal.String.Regex */
    blockquote c-[ss] { color: inherit; } /* Literal.String.Symbol */
    blockquote c-[vc] { color: inherit; } /* Name.Variable.Class */
    blockquote c-[vg] { color: inherit; } /* Name.Variable.Global */
    blockquote c-[vi] { color: inherit; } /* Name.Variable.Instance */
    blockquote c-[il] { color: inherit; } /* Literal.Number.Integer.Long */
  </style>
  <meta content="Bikeshed version 74068a90b, updated Wed Mar 22 17:34:51 2023 -0700" name="generator">
  <link href="http://wg21.link/P2933R3" rel="canonical">
  <link href="https://isocpp.org/favicon.ico" rel="icon">
  <meta content="d97a157cea17280f3924caec4f7e83b17d28f88a" name="document-revision">
<style>
.ins, ins, ins * {
    background-color: rgb(200, 250, 200);
    color: rgb(0, 136, 0);
    text-decoration: none;
}
.span, span, span * {
    white-space: pre
}
</style>
<style>/* style-autolinks */
.css.css, .property.property, .descriptor.descriptor {
    color: var(--a-normal-text);
    font-size: inherit;
    font-family: inherit;
}
.css::before, .property::before, .descriptor::before {
    content: "‘";
}
.css::after, .property::after, .descriptor::after {
    content: "’";
}
.property, .descriptor {
    /* Don't wrap property and descriptor names */
    white-space: nowrap;
}
.type { /* CSS value <type> */
    font-style: italic;
}
pre .property::before, pre .property::after {
    content: "";
}
[data-link-type="property"]::before,
[data-link-type="propdesc"]::before,
[data-link-type="descriptor"]::before,
[data-link-type="value"]::before,
[data-link-type="function"]::before,
[data-link-type="at-rule"]::before,
[data-link-type="selector"]::before,
[data-link-type="maybe"]::before {
    content: "‘";
}
[data-link-type="property"]::after,
[data-link-type="propdesc"]::after,
[data-link-type="descriptor"]::after,
[data-link-type="value"]::after,
[data-link-type="function"]::after,
[data-link-type="at-rule"]::after,
[data-link-type="selector"]::after,
[data-link-type="maybe"]::after {
    content: "’";
}

[data-link-type].production::before,
[data-link-type].production::after,
.prod [data-link-type]::before,
.prod [data-link-type]::after {
    content: "";
}

[data-link-type=element],
[data-link-type=element-attr] {
    font-family: Menlo, Consolas, "DejaVu Sans Mono", monospace;
    font-size: .9em;
}
[data-link-type=element]::before { content: "<" }
[data-link-type=element]::after  { content: ">" }

[data-link-type=biblio] {
    white-space: pre;
}
</style>
<style>/* style-colors */

/* Any --*-text not paired with a --*-bg is assumed to have a transparent bg */
:root {
    color-scheme: light dark;

    --text: black;
    --bg: white;

    --unofficial-watermark: url(https://www.w3.org/StyleSheets/TR/2016/logos/UD-watermark);

    --logo-bg: #1a5e9a;
    --logo-active-bg: #c00;
    --logo-text: white;

    --tocnav-normal-text: #707070;
    --tocnav-normal-bg: var(--bg);
    --tocnav-hover-text: var(--tocnav-normal-text);
    --tocnav-hover-bg: #f8f8f8;
    --tocnav-active-text: #c00;
    --tocnav-active-bg: var(--tocnav-normal-bg);

    --tocsidebar-text: var(--text);
    --tocsidebar-bg: #f7f8f9;
    --tocsidebar-shadow: rgba(0,0,0,.1);
    --tocsidebar-heading-text: hsla(203,20%,40%,.7);

    --toclink-text: var(--text);
    --toclink-underline: #3980b5;
    --toclink-visited-text: var(--toclink-text);
    --toclink-visited-underline: #054572;

    --heading-text: #005a9c;

    --hr-text: var(--text);

    --algo-border: #def;

    --del-text: red;
    --del-bg: transparent;
    --ins-text: #080;
    --ins-bg: transparent;

    --a-normal-text: #034575;
    --a-normal-underline: #bbb;
    --a-visited-text: var(--a-normal-text);
    --a-visited-underline: #707070;
    --a-hover-bg: rgba(75%, 75%, 75%, .25);
    --a-active-text: #c00;
    --a-active-underline: #c00;

    --blockquote-border: silver;
    --blockquote-bg: transparent;
    --blockquote-text: currentcolor;

    --issue-border: #e05252;
    --issue-bg: #fbe9e9;
    --issue-text: var(--text);
    --issueheading-text: #831616;

    --example-border: #e0cb52;
    --example-bg: #fcfaee;
    --example-text: var(--text);
    --exampleheading-text: #574b0f;

    --note-border: #52e052;
    --note-bg: #e9fbe9;
    --note-text: var(--text);
    --noteheading-text: hsl(120, 70%, 30%);
    --notesummary-underline: silver;

    --assertion-border: #aaa;
    --assertion-bg: #eee;
    --assertion-text: black;

    --advisement-border: orange;
    --advisement-bg: #fec;
    --advisement-text: var(--text);
    --advisementheading-text: #b35f00;

    --warning-border: red;
    --warning-bg: hsla(40,100%,50%,0.95);
    --warning-text: var(--text);

    --amendment-border: #330099;
    --amendment-bg: #F5F0FF;
    --amendment-text: var(--text);
    --amendmentheading-text: #220066;

    --def-border: #8ccbf2;
    --def-bg: #def;
    --def-text: var(--text);
    --defrow-border: #bbd7e9;

    --datacell-border: silver;

    --indexinfo-text: #707070;

    --indextable-hover-text: black;
    --indextable-hover-bg: #f7f8f9;

    --outdatedspec-bg: rgba(0, 0, 0, .5);
    --outdatedspec-text: black;
    --outdated-bg: maroon;
    --outdated-text: white;
    --outdated-shadow: red;

    --editedrec-bg: darkorange;
}
</style>
<style>/* style-counters */
body {
    counter-reset: example figure issue;
}
.issue {
    counter-increment: issue;
}
.issue:not(.no-marker)::before {
    content: "Issue " counter(issue);
}

.example {
    counter-increment: example;
}
.example:not(.no-marker)::before {
    content: "Example " counter(example);
}
.invalid.example:not(.no-marker)::before,
.illegal.example:not(.no-marker)::before {
    content: "Invalid Example" counter(example);
}

figcaption {
    counter-increment: figure;
}
figcaption:not(.no-marker)::before {
    content: "Figure " counter(figure) " ";
}
</style>
<style>/* style-issues */
a[href].issue-return {
    float: right;
    float: inline-end;
    color: var(--issueheading-text);
    font-weight: bold;
    text-decoration: none;
}
</style>
<style>/* style-md-lists */
/* This is a weird hack for me not yet following the commonmark spec
   regarding paragraph and lists. */
[data-md] > :first-child {
    margin-top: 0;
}
[data-md] > :last-child {
    margin-bottom: 0;
}
</style>
<style>/* style-selflinks */

:root {
    --selflink-text: white;
    --selflink-bg: gray;
    --selflink-hover-text: black;
}
.heading, .issue, .note, .example, li, dt {
    position: relative;
}
a.self-link {
    position: absolute;
    top: 0;
    left: calc(-1 * (3.5rem - 26px));
    width: calc(3.5rem - 26px);
    height: 2em;
    text-align: center;
    border: none;
    transition: opacity .2s;
    opacity: .5;
}
a.self-link:hover {
    opacity: 1;
}
.heading > a.self-link {
    font-size: 83%;
}
.example > a.self-link,
.note > a.self-link,
.issue > a.self-link {
    /* These blocks are overflow:auto, so positioning outside
       doesn't work. */
    left: auto;
    right: 0;
}
li > a.self-link {
    left: calc(-1 * (3.5rem - 26px) - 2em);
}
dfn > a.self-link {
    top: auto;
    left: auto;
    opacity: 0;
    width: 1.5em;
    height: 1.5em;
    background: var(--selflink-bg);
    color: var(--selflink-text);
    font-style: normal;
    transition: opacity .2s, background-color .2s, color .2s;
}
dfn:hover > a.self-link {
    opacity: 1;
}
dfn > a.self-link:hover {
    color: var(--selflink-hover-text);
}

a.self-link::before            { content: "¶"; }
.heading > a.self-link::before { content: "§"; }
dfn > a.self-link::before      { content: "#"; }
</style>
<style>/* style-syntax-highlighting */

code.highlight { padding: .1em; border-radius: .3em; }
pre.highlight, pre > code.highlight { display: block; padding: 1em; margin: .5em 0; overflow: auto; border-radius: 0; }

.highlight:not(.idl) { background: rgba(0, 0, 0, .03); }
c-[a] { color: #990055 } /* Keyword.Declaration */
c-[b] { color: #990055 } /* Keyword.Type */
c-[c] { color: #708090 } /* Comment */
c-[d] { color: #708090 } /* Comment.Multiline */
c-[e] { color: #0077aa } /* Name.Attribute */
c-[f] { color: #669900 } /* Name.Tag */
c-[g] { color: #222222 } /* Name.Variable */
c-[k] { color: #990055 } /* Keyword */
c-[l] { color: #000000 } /* Literal */
c-[m] { color: #000000 } /* Literal.Number */
c-[n] { color: #0077aa } /* Name */
c-[o] { color: #999999 } /* Operator */
c-[p] { color: #999999 } /* Punctuation */
c-[s] { color: #a67f59 } /* Literal.String */
c-[t] { color: #a67f59 } /* Literal.String.Single */
c-[u] { color: #a67f59 } /* Literal.String.Double */
c-[cp] { color: #708090 } /* Comment.Preproc */
c-[c1] { color: #708090 } /* Comment.Single */
c-[cs] { color: #708090 } /* Comment.Special */
c-[kc] { color: #990055 } /* Keyword.Constant */
c-[kn] { color: #990055 } /* Keyword.Namespace */
c-[kp] { color: #990055 } /* Keyword.Pseudo */
c-[kr] { color: #990055 } /* Keyword.Reserved */
c-[ld] { color: #000000 } /* Literal.Date */
c-[nc] { color: #0077aa } /* Name.Class */
c-[no] { color: #0077aa } /* Name.Constant */
c-[nd] { color: #0077aa } /* Name.Decorator */
c-[ni] { color: #0077aa } /* Name.Entity */
c-[ne] { color: #0077aa } /* Name.Exception */
c-[nf] { color: #0077aa } /* Name.Function */
c-[nl] { color: #0077aa } /* Name.Label */
c-[nn] { color: #0077aa } /* Name.Namespace */
c-[py] { color: #0077aa } /* Name.Property */
c-[ow] { color: #999999 } /* Operator.Word */
c-[mb] { color: #000000 } /* Literal.Number.Bin */
c-[mf] { color: #000000 } /* Literal.Number.Float */
c-[mh] { color: #000000 } /* Literal.Number.Hex */
c-[mi] { color: #000000 } /* Literal.Number.Integer */
c-[mo] { color: #000000 } /* Literal.Number.Oct */
c-[sb] { color: #a67f59 } /* Literal.String.Backtick */
c-[sc] { color: #a67f59 } /* Literal.String.Char */
c-[sd] { color: #a67f59 } /* Literal.String.Doc */
c-[se] { color: #a67f59 } /* Literal.String.Escape */
c-[sh] { color: #a67f59 } /* Literal.String.Heredoc */
c-[si] { color: #a67f59 } /* Literal.String.Interpol */
c-[sx] { color: #a67f59 } /* Literal.String.Other */
c-[sr] { color: #a67f59 } /* Literal.String.Regex */
c-[ss] { color: #a67f59 } /* Literal.String.Symbol */
c-[vc] { color: #0077aa } /* Name.Variable.Class */
c-[vg] { color: #0077aa } /* Name.Variable.Global */
c-[vi] { color: #0077aa } /* Name.Variable.Instance */
c-[il] { color: #000000 } /* Literal.Number.Integer.Long */
</style>
<style>/* style-darkmode */

@media (prefers-color-scheme: dark) {
    :root {
        --text: #ddd;
        --bg: black;

        --unofficial-watermark: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='400' height='400'%3E%3Cg fill='%23100808' transform='translate(200 200) rotate(-45) translate(-200 -200)' stroke='%23100808' stroke-width='3'%3E%3Ctext x='50%25' y='220' style='font: bold 70px sans-serif; text-anchor: middle; letter-spacing: 6px;'%3EUNOFFICIAL%3C/text%3E%3Ctext x='50%25' y='305' style='font: bold 70px sans-serif; text-anchor: middle; letter-spacing: 6px;'%3EDRAFT%3C/text%3E%3C/g%3E%3C/svg%3E");

        --logo-bg: #1a5e9a;
        --logo-active-bg: #c00;
        --logo-text: white;

        --tocnav-normal-text: #999;
        --tocnav-normal-bg: var(--bg);
        --tocnav-hover-text: var(--tocnav-normal-text);
        --tocnav-hover-bg: #080808;
        --tocnav-active-text: #f44;
        --tocnav-active-bg: var(--tocnav-normal-bg);

        --tocsidebar-text: var(--text);
        --tocsidebar-bg: #080808;
        --tocsidebar-shadow: rgba(255,255,255,.1);
        --tocsidebar-heading-text: hsla(203,20%,40%,.7);

        --toclink-text: var(--text);
        --toclink-underline: #6af;
        --toclink-visited-text: var(--toclink-text);
        --toclink-visited-underline: #054572;

        --heading-text: #8af;

        --hr-text: var(--text);

        --algo-border: #456;

        --del-text: #f44;
        --del-bg: transparent;
        --ins-text: #4a4;
        --ins-bg: transparent;

        --a-normal-text: #6af;
        --a-normal-underline: #555;
        --a-visited-text: var(--a-normal-text);
        --a-visited-underline: var(--a-normal-underline);
        --a-hover-bg: rgba(25%, 25%, 25%, .2);
        --a-active-text: #f44;
        --a-active-underline: var(--a-active-text);

        --borderedblock-bg: rgba(255, 255, 255, .05);

        --blockquote-border: silver;
        --blockquote-bg: var(--borderedblock-bg);
        --blockquote-text: currentcolor;

        --issue-border: #e05252;
        --issue-bg: var(--borderedblock-bg);
        --issue-text: var(--text);
        --issueheading-text: hsl(0deg, 70%, 70%);

        --example-border: hsl(50deg, 90%, 60%);
        --example-bg: var(--borderedblock-bg);
        --example-text: var(--text);
        --exampleheading-text: hsl(50deg, 70%, 70%);

        --note-border: hsl(120deg, 100%, 35%);
        --note-bg: var(--borderedblock-bg);
        --note-text: var(--text);
        --noteheading-text: hsl(120, 70%, 70%);
        --notesummary-underline: silver;

        --assertion-border: #444;
        --assertion-bg: var(--borderedblock-bg);
        --assertion-text: var(--text);

        --advisement-border: orange;
        --advisement-bg: #222218;
        --advisement-text: var(--text);
        --advisementheading-text: #f84;

        --warning-border: red;
        --warning-bg: hsla(40,100%,20%,0.95);
        --warning-text: var(--text);

        --amendment-border: #330099;
        --amendment-bg: #080010;
        --amendment-text: var(--text);
        --amendmentheading-text: #cc00ff;

        --def-border: #8ccbf2;
        --def-bg: #080818;
        --def-text: var(--text);
        --defrow-border: #136;

        --datacell-border: silver;

        --indexinfo-text: #aaa;

        --indextable-hover-text: var(--text);
        --indextable-hover-bg: #181818;

        --outdatedspec-bg: rgba(255, 255, 255, .5);
        --outdatedspec-text: black;
        --outdated-bg: maroon;
        --outdated-text: white;
        --outdated-shadow: red;

        --editedrec-bg: darkorange;
    }
    /* In case a transparent-bg image doesn't expect to be on a dark bg,
       which is quite common in practice... */
    img { background: white; }
}

@media (prefers-color-scheme: dark) {
    :root {
        --selflink-text: black;
        --selflink-bg: silver;
        --selflink-hover-text: white;
    }
}

@media (prefers-color-scheme: dark) {
    .highlight:not(.idl) { background: rgba(255, 255, 255, .05); }

    c-[a] { color: #d33682 } /* Keyword.Declaration */
    c-[b] { color: #d33682 } /* Keyword.Type */
    c-[c] { color: #2aa198 } /* Comment */
    c-[d] { color: #2aa198 } /* Comment.Multiline */
    c-[e] { color: #268bd2 } /* Name.Attribute */
    c-[f] { color: #b58900 } /* Name.Tag */
    c-[g] { color: #cb4b16 } /* Name.Variable */
    c-[k] { color: #d33682 } /* Keyword */
    c-[l] { color: #657b83 } /* Literal */
    c-[m] { color: #657b83 } /* Literal.Number */
    c-[n] { color: #268bd2 } /* Name */
    c-[o] { color: #657b83 } /* Operator */
    c-[p] { color: #657b83 } /* Punctuation */
    c-[s] { color: #6c71c4 } /* Literal.String */
    c-[t] { color: #6c71c4 } /* Literal.String.Single */
    c-[u] { color: #6c71c4 } /* Literal.String.Double */
    c-[ch] { color: #2aa198 } /* Comment.Hashbang */
    c-[cp] { color: #2aa198 } /* Comment.Preproc */
    c-[cpf] { color: #2aa198 } /* Comment.PreprocFile */
    c-[c1] { color: #2aa198 } /* Comment.Single */
    c-[cs] { color: #2aa198 } /* Comment.Special */
    c-[kc] { color: #d33682 } /* Keyword.Constant */
    c-[kn] { color: #d33682 } /* Keyword.Namespace */
    c-[kp] { color: #d33682 } /* Keyword.Pseudo */
    c-[kr] { color: #d33682 } /* Keyword.Reserved */
    c-[ld] { color: #657b83 } /* Literal.Date */
    c-[nc] { color: #268bd2 } /* Name.Class */
    c-[no] { color: #268bd2 } /* Name.Constant */
    c-[nd] { color: #268bd2 } /* Name.Decorator */
    c-[ni] { color: #268bd2 } /* Name.Entity */
    c-[ne] { color: #268bd2 } /* Name.Exception */
    c-[nf] { color: #268bd2 } /* Name.Function */
    c-[nl] { color: #268bd2 } /* Name.Label */
    c-[nn] { color: #268bd2 } /* Name.Namespace */
    c-[py] { color: #268bd2 } /* Name.Property */
    c-[ow] { color: #657b83 } /* Operator.Word */
    c-[mb] { color: #657b83 } /* Literal.Number.Bin */
    c-[mf] { color: #657b83 } /* Literal.Number.Float */
    c-[mh] { color: #657b83 } /* Literal.Number.Hex */
    c-[mi] { color: #657b83 } /* Literal.Number.Integer */
    c-[mo] { color: #657b83 } /* Literal.Number.Oct */
    c-[sa] { color: #6c71c4 } /* Literal.String.Affix */
    c-[sb] { color: #6c71c4 } /* Literal.String.Backtick */
    c-[sc] { color: #6c71c4 } /* Literal.String.Char */
    c-[dl] { color: #6c71c4 } /* Literal.String.Delimiter */
    c-[sd] { color: #6c71c4 } /* Literal.String.Doc */
    c-[se] { color: #6c71c4 } /* Literal.String.Escape */
    c-[sh] { color: #6c71c4 } /* Literal.String.Heredoc */
    c-[si] { color: #6c71c4 } /* Literal.String.Interpol */
    c-[sx] { color: #6c71c4 } /* Literal.String.Other */
    c-[sr] { color: #6c71c4 } /* Literal.String.Regex */
    c-[ss] { color: #6c71c4 } /* Literal.String.Symbol */
    c-[fm] { color: #268bd2 } /* Name.Function.Magic */
    c-[vc] { color: #cb4b16 } /* Name.Variable.Class */
    c-[vg] { color: #cb4b16 } /* Name.Variable.Global */
    c-[vi] { color: #cb4b16 } /* Name.Variable.Instance */
    c-[vm] { color: #cb4b16 } /* Name.Variable.Magic */
    c-[il] { color: #657b83 } /* Literal.Number.Integer.Long */
}
</style>
 <body class="h-entry">
  <div class="head">
   <p data-fill-with="logo"></p>
   <h1 class="p-name no-ref" id="title">P2993R3<br>Extend <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code> header function with overloads for <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code></h1>
   <h2 class="no-num no-toc no-ref heading settled" id="profile-and-date"><span class="content">Published Proposal, <time class="dt-updated" datetime="2025-01-13">2025-01-13</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt>This version:
     <dd><a class="u-url" href="http://wg21.link/P2933R3">http://wg21.link/P2933R3</a>
     <dt class="editor">Authors:
     <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:daniel.towner@intel.com">Daniel Towner</a> (<span class="p-org org">Intel</span>)
     <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:ruslan.arutyunyan@intel.com">Ruslan Arutyunyan</a> (<span class="p-org org">Intel</span>)
     <dt>Audience:
     <dd>LEWG
     <dt>Project:
     <dd>ISO/IEC 14882 Programming Languages — C++, ISO/IEC JTC1/SC22/WG21
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p>Proposal to extend <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code> with overloads from other C++ standard libraries</p>
  </div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li><a href="#intro"><span class="secno">1</span> <span class="content">Motivation</span></a>
    <li><a href="#support_bit"><span class="secno">2</span> <span class="content">Support for <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code></span></a>
    <li><a href="#design_confirm_lewg"><span class="secno">3</span> <span class="content">Design confirmation request from LWG</span></a>
    <li>
     <a href="#wording"><span class="secno">4</span> <span class="content">Wording</span></a>
     <ol class="toc">
      <li><a href="#wording_feature_test"><span class="secno">4.1</span> <span class="content">Add new section in [<strong>version.syn</strong>]</span></a>
      <li><a href="#wording_exposition"><span class="secno">4.2</span> <span class="content">Modify [<strong>simd.expos</strong>]</span></a>
      <li><a href="#wording_synopsis"><span class="secno">4.3</span> <span class="content">Update the synopsis</span></a>
      <li><a href="#wording_simd_bit"><span class="secno">4.4</span> <span class="content">Add new section [<strong>simd.bit</strong>] after [<strong>simd.math</strong>]</span></a>
     </ol>
    <li><a href="#revision_history"><span class="secno">5</span> <span class="content">Revision History</span></a>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
     </ol>
   </ol>
  </nav>
  <main>
   <h2 class="heading settled" data-level="1" id="intro"><span class="secno">1. </span><span class="content">Motivation</span><a class="self-link" href="#intro"></a></h2>
   <p><a data-link-type="biblio" href="#biblio-p1928r7" title="std::simd - Merge data-parallel types from the Parallelism TS 2">[P1928R7]</a> introduced data parallel types to C++. It mostly provided operators
which worked on or with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code> types, but it also included overloads of
useful functions from other parts of C++ (e.g., sin, cos, abs). In this paper we
propose some other functions from standard C++ headers which should receive
overloads to work with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code> types. The list isn’t exhaustive, but
reflects those functions which are desirable to include.</p>
   <h2 class="heading settled" data-level="2" id="support_bit"><span class="secno">2. </span><span class="content">Support for <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code></span><a class="self-link" href="#support_bit"></a></h2>
   <p>The <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code> header is part of the numerics library and provides utilities for
manipulating and querying the properties of integral values when treated as
collections of bits. The table below summarises the contents of <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code>.</p>
   <table>
    <tbody>
     <tr>
      <th>Name
      <th>Purpose
      <th>Proposed (Y/N)
     <tr>
      <td><code class="highlight"><c- n>endian</c-></code>
      <td>A type which indicates the endianness of scalar types.
      <td style="text-align: center">N
     <tr>
      <td><code class="highlight"><c- n>bit_cast</c-></code>
      <td>reinterpret the object representation of one type as that of another
      <td style="text-align: center">N
     <tr>
      <td><code class="highlight"><c- n>byteswap</c-></code>
      <td>reverses the bytes in the given integer value
      <td style="text-align: center">Y
     <tr>
      <td><code class="highlight"><c- n>has_single_bit</c-></code>
      <td>checks if a number is an integral power of two
      <td style="text-align: center">Y
     <tr>
      <td><code class="highlight"><c- n>bit_ceil</c-></code>
      <td>finds the smallest integral power of two not less than the given value
      <td style="text-align: center">Y
     <tr>
      <td><code class="highlight"><c- n>bit_floor</c-></code>
      <td>finds the largest integral power of two not greater than the given value
      <td style="text-align: center">Y
     <tr>
      <td><code class="highlight"><c- n>bit_width</c-></code>
      <td>finds the smallest number of bits needed to represent the given value
      <td style="text-align: center">Y
     <tr>
      <td><code class="highlight"><c- n>rotl</c-></code>
      <td>computes the result of bitwise left-rotation
      <td style="text-align: center">Y
     <tr>
      <td><code class="highlight"><c- n>rotr</c-></code>
      <td>computes the result of bitwise right-rotation
      <td style="text-align: center">Y
     <tr>
      <td><code class="highlight"><c- n>countl_zero</c-></code>
      <td>counts the number of consecutive 0 bits, starting from the most significant bit
      <td style="text-align: center">Y
     <tr>
      <td><code class="highlight"><c- n>countl_one</c-></code>
      <td>counts the number of consecutive 1 bits, starting from the most significant bit
      <td style="text-align: center">Y
     <tr>
      <td><code class="highlight"><c- n>countr_zero</c-></code>
      <td>counts the number of consecutive 0 bits, starting from the least significant bit
      <td style="text-align: center">Y
     <tr>
      <td><code class="highlight"><c- n>countr_one</c-></code>
      <td>counts the number of consecutive 1 bits, starting from the least significant bit
      <td style="text-align: center">Y
     <tr>
      <td><code class="highlight"><c- n>popcount</c-></code>
      <td>counts the number of 1 bits in an unsigned integer
      <td style="text-align: center">Y
   </table>
   <p>Of these types and functions, only the first two shouldn’t be handled by <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code>:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>endian</c-></code> indicates the endianess of a scalar type. A SIMD value with elements
of the underlying scalar type will have the same properties and does not do a
special handling in <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code>.</p>
    <li data-md>
     <p><code class="highlight"><c- n>bit_cast</c-></code> should be handled differently for <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code> values, and a
separate proposal for <code class="highlight"><c- n>simd_bit_cast</c-></code> will be provided.</p>
   </ul>
   <p>All the other functions from <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code> should be handled in <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code> by
element-wise application of the function to each element of the SIMD value. Any
constraints and behaviours on the function will be applied at the SIMD value
level. For instance, if <code class="highlight"><c- n>byteswap</c-></code> participates in overload resolution only if the argument type satisfies <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>integral</c-></code> concept then the overload of <code class="highlight"><c- n>byteswap</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code> parameter has the same constraint for <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>N</c-><c- o>>::</c-><c- n>value_type</c-></code>.</p>
   <p>One small modification to the behaviour of <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code> for <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code> is where the return
type differs to the input type. For example, the standard <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code> header defines
some query functions as returning integer values:</p>
<pre class="language-cpp highlight"><c- k>template</c-><c- o>&lt;</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>></c->
<c- k>constexpr</c-> <c- b>int</c-> <c- n>bit_width</c-><c- p>(</c-> <c- n>T</c-> <c- n>x</c-> <c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->

<c- k>template</c-><c- o>&lt;</c-> <c- k>class</c-> <c- nc>T</c-> <c- o>></c->
<c- k>constexpr</c-> <c- b>int</c-> <c- n>countl_one</c-><c- p>(</c-> <c- n>T</c-> <c- n>x</c-> <c- p>)</c-> <c- k>noexcept</c-><c- p>;</c-></pre>
   <p>If an <code class="highlight"><c- b>int</c-></code> were to be returned from the <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code> overload of such functions
then the size of the elements could change. For example, computing
the bit width of a 8-bit integer could generate a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code> of 64-bit integers as the
output, which would lead to a dramatic change in storage size and performance.
Instead, we propose that all the overloads for <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code> should return element
types which are the same physical size as the element types they are querying.
This would mean that calling <code class="highlight"><c- n>bit_width</c-></code> on an <code class="highlight"><c- b>unsigned</c-></code> 8-bit integer will
return a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>simd</c-></code> containing signed 8-bit values.</p>
   <p>When calling the rotate functions <code class="highlight"><c- n>rotl</c-></code> and <code class="highlight"><c- n>rotr</c-></code> functions it is common to
want to rotate all simd elements by the same amount. An overload will be
provided which takes a scalar <code class="highlight"><c- b>int</c-></code> value to match <code class="highlight"><c- n>rotl</c-></code> and <code class="highlight"><c- n>rotr</c-></code> in the <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code> header. In this case there is no need to supply an integer of the same
width as the first parameter’s elements (as described above for the <code class="highlight"><c- n>simd</c-></code> variant) since broadcasting an <code class="highlight"><c- n>integer</c-></code> to a <code class="highlight"><c- n>simd</c-></code> has negligible performance
impact.</p>
   <h2 class="heading settled" data-level="3" id="design_confirm_lewg"><span class="secno">3. </span><span class="content">Design confirmation request from LWG</span><a class="self-link" href="#design_confirm_lewg"></a></h2>
   <p>During LWG review it was suggested that the <code class="highlight"><c- n>rotl</c-></code> and <code class="highlight"><c- n>rotr</c-></code> functions should provide an overload for the common case where a scalar could to be used as the second parameter. This paper has been updated to reflect that change, and we would like LEWG to confirm acceptance of this design change.</p>
   <h2 class="heading settled" data-level="4" id="wording"><span class="secno">4. </span><span class="content">Wording</span><a class="self-link" href="#wording"></a></h2>
   <p>Below, substitute the � character with a number the editor finds appropriate for
the table, paragraph, section or sub-section.</p>
   <h3 class="heading settled" data-level="4.1" id="wording_feature_test"><span class="secno">4.1. </span><span class="content">Add new section in [<strong>version.syn</strong>]</span><a class="self-link" href="#wording_feature_test"></a></h3>
   <p>In [version.syn] bump the <code class="highlight"><c- n>__cpp_lib_simd</c-></code> version.</p>
   <h3 class="heading settled" data-level="4.2" id="wording_exposition"><span class="secno">4.2. </span><span class="content">Modify [<strong>simd.expos</strong>]</span><a class="self-link" href="#wording_exposition"></a></h3>
   <blockquote>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>V</c-><c- o>></c->
  <c- k>concept</c-> <i><c- nc>simd</c-><c- o>-</c-><c- n>floating</c-><c- o>-</c-><c- n>point</c-></i> <c- o>=</c-> <c- c1>// </c-><i><c- c1>exposition only</c-></i>
     <c- n>same_as</c-><c- o>&lt;</c-><c- n>V</c-><c- p>,</c-> <c- n>basic_simd</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- p>,</c-> <c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>abi_type</c-><c- o>>></c-> <c- o>&amp;&amp;</c->
     <c- n>is_default_constructible_v</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>floating_point</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>;</c-></pre>
   </blockquote>
   <ins>
    <blockquote>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>V</c-><c- o>></c->
  <c- k>concept</c-> <i><c- nc>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- o>=</c-> <c- c1>// </c-><i><c- c1>exposition only</c-></i>
     <c- n>same_as</c-><c- o>&lt;</c-><c- n>V</c-><c- p>,</c-> <c- n>basic_simd</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- p>,</c-> <c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>abi_type</c-><c- o>>></c-> <c- o>&amp;&amp;</c->
     <c- n>is_default_constructible_v</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>;</c-></pre>
    </blockquote>
   </ins>
   <h3 class="heading settled" data-level="4.3" id="wording_synopsis"><span class="secno">4.3. </span><span class="content">Update the synopsis</span><a class="self-link" href="#wording_synopsis"></a></h3>
   <p>In the header <code class="highlight"><c- o>&lt;</c-><c- n>simd</c-><c- o>></c-></code> synopsis - [simd.syn] - add at the end after the "Mathematical functions"</p>
   <ins>
    <blockquote>
<pre class="highlight"><span class="wording"><i><c- c1>// [simd.bit], Bit manipulation</c-></i><c- c1> </c-><bit>
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>V</c-> <c- n>byteswap</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>V</c-> <c- n>bit_ceil</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>V</c-> <c- n>bit_floor</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->

<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>mask_type</c-> <c- n>has_single_bit</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->

<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V0</c-><c- p>,</c-> <i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V1</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>V</c-> <c- n>rotl</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>V1</c-><c- o>&amp;</c-> <c- n>s</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V0</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>V</c-> <c- n>rotl</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- b>int</c-> <c- n>s</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->

<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V0</c-><c- p>,</c-> <i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V1</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>V0</c-> <c- n>rotr</c-><c- p>(</c-><c- k>const</c-> <c- n>V0</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>V1</c-><c- o>&amp;</c-> <c- n>s</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V0</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>V0</c-> <c- n>rotr</c-><c- p>(</c-><c- k>const</c-> <c- n>V0</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- b>int</c-> <c- n>s</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->

<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>bit_width</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>countl_zero</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>countl_one</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>countr_zero</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>countr_one</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>popcount</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c-></bit></span></pre>
    </blockquote>
   </ins>
   <h3 class="heading settled" data-level="4.4" id="wording_simd_bit"><span class="secno">4.4. </span><span class="content">Add new section [<strong>simd.bit</strong>] after [<strong>simd.math</strong>]</span><a class="self-link" href="#wording_simd_bit"></a></h3>
   <ins>
    <blockquote>
     <p><b><span class="wording"> � <code class="highlight"><c- n>basic_simd</c-></code> bit library        [simd.bit]</span></b></p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->              <c- k>constexpr</c-> <c- n>V</c-> <c- n>byteswap</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c-></pre>
     <p><i>Constraints</i>:</p>
     <p>Any constraints from the corresponding scalar function <code class="highlight"><c- n>byteswap</c-></code> are applied to <code class="highlight"><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-></code>.</p>
     <p><i>Returns</i>:</p>
     <p>The result of the element-wise application of <code class="highlight"><c- n>byteswap</c-><c- p>(</c-><c- n>x</c-><c- p>[</c-><c- n>i</c-><c- p>])</c-></code> for all <i>i</i> in the range of <code class="highlight"><c- p>[</c-><c- mi>0</c-><c- p>,</c-> <c- n>V</c-><c- o>::</c-><c- n>size</c-><c- p>]</c-></code>.</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>V</c-> <c- n>bit_ceil</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>V</c-> <c- n>bit_floor</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c-> <c- k>constexpr</c-> <c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>mask_type</c-> <c- n>has_single_bit</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>x</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c-></pre>
     <p><i>Constraints</i>:</p>
     <p>Any constraints from the corresponding scalar function from &lt;bit> are applied to <code class="highlight"><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-></code>.</p>
     <p><i>Returns</i>:</p>
     <p>The result of the element-wise application of <i><code class="highlight"><c- n>bit</c-><c- o>-</c-><c- n>func</c-><c- p>(</c-><c- n>x</c-><c- p>[</c-><c- n>i</c-><c- p>])</c-></code></i> for
    all <i>i</i> in the range of <code class="highlight"><c- p>[</c-><c- mi>0</c-><c- p>,</c-> <c- n>V</c-><c- o>::</c-><c- n>size</c-><c- p>]</c-></code>, where <i><code class="highlight"><c- n>bit</c-><c- o>-</c-><c- n>func</c-></code></i> is the corresponding scalar function from <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code>.</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V0</c-><c- p>,</c-> <i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V1</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>V0</c-> <c- n>rotl</c-><c- p>(</c-><c- k>const</c-> <c- n>V0</c-><c- o>&amp;</c-> <c- n>v0</c-><c- p>,</c-> <c- k>const</c-> <c- n>V1</c-><c- o>&amp;</c-> <c- n>v1</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V0</c-><c- p>,</c-> <i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V1</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>V0</c-> <c- n>rotr</c-><c- p>(</c-><c- k>const</c-> <c- n>V0</c-><c- o>&amp;</c-> <c- n>v0</c-><c- p>,</c-> <c- k>const</c-> <c- n>V1</c-><c- o>&amp;</c-> <c- n>v1</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c-></pre>
     <p><i>Constraints</i>:</p>
     <ul>
      <li data-md>
       <p>Any constraints from the corresponding scalar function from &lt;bit> are applied to <code class="highlight"><c- k>typename</c-> <c- nc>V0</c-><c- o>::</c-><c- n>value_type</c-></code>.</p>
      <li data-md>
       <p><code class="highlight"><c- k>sizeof</c-><c- p>(</c-><c- k>typename</c-> <c- nc>V0</c-><c- o>::</c-><c- n>value_type</c-><c- p>)</c-> <c- o>==</c-> <c- k>sizeof</c-><c- p>(</c-><c- k>typename</c-> <c- nc>V1</c-><c- o>::</c-><c- n>value_type</c-><c- p>)</c-></code> is <code class="highlight">true</code>.</p>
     </ul>
     <p><i>Returns</i>:</p>
     <p>The result of the element-wise application of <i><code class="highlight"><c- n>bit</c-><c- o>-</c-><c- n>func</c-><c- p>(</c-><c- n>v0</c-><c- p>[</c-><c- n>i</c-><c- p>],</c-> <c- n>v1</c-><c- p>[</c-><c- n>i</c-><c- p>])</c-></code></i> for
    all <i>i</i> in the range of <code class="highlight"><c- p>[</c-><c- mi>0</c-><c- p>,</c-> <c- n>V</c-><c- o>::</c-><c- n>size</c-><c- p>]</c-></code>, where <i><code class="highlight"><c- n>bit</c-><c- o>-</c-><c- n>func</c-></code></i> is the corresponding scalar function from <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code>.</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>V</c-> <c- n>rotl</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>,</c-> <c- b>int</c-> <c- n>s</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c-> <c- k>constexpr</c-> <c- n>V</c-> <c- n>rotr</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>,</c-> <c- b>int</c-> <c- n>s</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c-></pre>
     <p><i>Constraints</i>:</p>
     <p>Any constraints from the corresponding scalar function from &lt;bit> are applied to <code class="highlight"><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-></code>.</p>
     <p><i>Returns</i>:</p>
     <p>The result of the element-wise application of <i><code class="highlight"><c- n>bit</c-><c- o>-</c-><c- n>func</c-><c- p>(</c-><c- n>v</c-><c- p>[</c-><c- n>i</c-><c- p>],</c-> <c- n>s</c-><c- p>)</c-></code></i> for
    all <i>i</i> in the range of <code class="highlight"><c- p>[</c-><c- mi>0</c-><c- p>,</c-> <c- n>V</c-><c- o>::</c-><c- n>size</c-><c- p>]</c-></code>, where <i><code class="highlight"><c- n>bit</c-><c- o>-</c-><c- n>func</c-></code></i> is the corresponding scalar function from <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code>.</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>bit_width</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>countl_zero</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>countl_one</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>countr_zero</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>countr_one</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
<c- k>template</c-><c- o>&lt;</c-><i><c- n>simd</c-><c- o>-</c-><c- n>type</c-></i> <c- n>V</c-><c- o>></c->
  <c- k>constexpr</c-> <c- n>rebind_simd_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-><c- o>&lt;</c-><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-><c- o>></c-><c- p>,</c-> <c- n>V</c-><c- o>></c->
  <c- n>popcount</c-><c- p>(</c-><c- k>const</c-> <c- n>V</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c-></pre>
     <p><i>Constraints</i>:</p>
     <p>Any constraints from the corresponding scalar function from &lt;bit> are applied to <code class="highlight"><c- k>typename</c-> <c- nc>V</c-><c- o>::</c-><c- n>value_type</c-></code>.</p>
     <p><i>Returns</i>:</p>
     <p>The result of the element-wise application of <i><code class="highlight"><c- n>bit</c-><c- o>-</c-><c- n>func</c-><c- p>(</c-><c- n>v</c-><c- p>[</c-><c- n>i</c-><c- p>],</c-> <c- n>s</c-><c- p>)</c-></code></i> for all <i>i</i> in the range of <code class="highlight"><c- p>[</c-><c- mi>0</c-><c- p>,</c-> <c- n>V</c-><c- o>::</c-><c- n>size</c-><c- p>]</c-></code>, where <i><code class="highlight"><c- n>bit</c-><c- o>-</c-><c- n>func</c-></code></i> is the corresponding scalar function from <code class="highlight"><c- o>&lt;</c-><c- n>bit</c-><c- o>></c-></code>. [<i>Note: the type of the return value elements is the signed version of the
    input element type. This is different to the equivalent scalar functions
    which always return an <code class="highlight"><c- b>int</c-></code> value.</i>]</p>
    </blockquote>
   </ins>
   <h2 class="heading settled" data-level="5" id="revision_history"><span class="secno">5. </span><span class="content">Revision History</span><a class="self-link" href="#revision_history"></a></h2>
   <p>R2 => R3</p>
   <ul>
    <li data-md>
     <p>Add missing synopsis wording addition.</p>
    <li data-md>
     <p>Change detailed behaviour descriptions to match the style/wording of recent P1928 updates.</p>
    <li data-md>
     <p>Added concepts to detect simd types whose elements are integral, unsigned, and so on.</p>
    <li data-md>
     <p>Added overload to rotl/rotr to allow the second parameter to be a scalar.</p>
   </ul>
   <p>R1 => R2</p>
   <ul>
    <li data-md>
     <p>Added feature test macro</p>
   </ul>
   <p>R0 => R1</p>
   <ul>
    <li data-md>
     <p>Fix typo: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>make_signed</c-></code> to <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>make_signed_t</c-></code></p>
    <li data-md>
     <p>Make several paper text improvements</p>
   </ul>
  </main>
<script>
(function() {
  "use strict";
  var collapseSidebarText = '<span aria-hidden="true">←</span> '
                          + '<span>Collapse Sidebar</span>';
  var expandSidebarText   = '<span aria-hidden="true">→</span> '
                          + '<span>Pop Out Sidebar</span>';
  var tocJumpText         = '<span aria-hidden="true">↑</span> '
                          + '<span>Jump to Table of Contents</span>';

  var sidebarMedia = window.matchMedia('screen and (min-width: 78em)');
  var autoToggle   = function(e){ toggleSidebar(e.matches) };
  if(sidebarMedia.addListener) {
    sidebarMedia.addListener(autoToggle);
  }

  function toggleSidebar(on) {
    if (on == undefined) {
      on = !document.body.classList.contains('toc-sidebar');
    }

    /* Don’t scroll to compensate for the ToC if we’re above it already. */
    var headY = 0;
    var head = document.querySelector('.head');
    if (head) {
      // terrible approx of "top of ToC"
      headY += head.offsetTop + head.offsetHeight;
    }
    var skipScroll = window.scrollY < headY;

    var toggle = document.getElementById('toc-toggle');
    var tocNav = document.getElementById('toc');
    if (on) {
      var tocHeight = tocNav.offsetHeight;
      document.body.classList.add('toc-sidebar');
      document.body.classList.remove('toc-inline');
      toggle.innerHTML = collapseSidebarText;
      if (!skipScroll) {
        window.scrollBy(0, 0 - tocHeight);
      }
      tocNav.focus();
      sidebarMedia.addListener(autoToggle); // auto-collapse when out of room
    }
    else {
      document.body.classList.add('toc-inline');
      document.body.classList.remove('toc-sidebar');
      toggle.innerHTML = expandSidebarText;
      if (!skipScroll) {
        window.scrollBy(0, tocNav.offsetHeight);
      }
      if (toggle.matches(':hover')) {
        /* Unfocus button when not using keyboard navigation,
           because I don’t know where else to send the focus. */
        toggle.blur();
      }
    }
  }

  function createSidebarToggle() {
    /* Create the sidebar toggle in JS; it shouldn’t exist when JS is off. */
    var toggle = document.createElement('a');
      /* This should probably be a button, but appearance isn’t standards-track.*/
    toggle.id = 'toc-toggle';
    toggle.class = 'toc-toggle';
    toggle.href = '#toc';
    toggle.innerHTML = collapseSidebarText;

    sidebarMedia.addListener(autoToggle);
    var toggler = function(e) {
      e.preventDefault();
      sidebarMedia.removeListener(autoToggle); // persist explicit off states
      toggleSidebar();
      return false;
    }
    toggle.addEventListener('click', toggler, false);


    /* Get <nav id=toc-nav>, or make it if we don’t have one. */
    var tocNav = document.getElementById('toc-nav');
    if (!tocNav) {
      tocNav = document.createElement('p');
      tocNav.id = 'toc-nav';
      /* Prepend for better keyboard navigation */
      document.body.insertBefore(tocNav, document.body.firstChild);
    }
    /* While we’re at it, make sure we have a Jump to Toc link. */
    var tocJump = document.getElementById('toc-jump');
    if (!tocJump) {
      tocJump = document.createElement('a');
      tocJump.id = 'toc-jump';
      tocJump.href = '#toc';
      tocJump.innerHTML = tocJumpText;
      tocNav.appendChild(tocJump);
    }

    tocNav.appendChild(toggle);
  }

  var toc = document.getElementById('toc');
  if (toc) {
    createSidebarToggle();
    toggleSidebar(sidebarMedia.matches);

    /* If the sidebar has been manually opened and is currently overlaying the text
       (window too small for the MQ to add the margin to body),
       then auto-close the sidebar once you click on something in there. */
    toc.addEventListener('click', function(e) {
      if(e.target.tagName.toLowerCase() == "a" && document.body.classList.contains('toc-sidebar') && !sidebarMedia.matches) {
        toggleSidebar(false);
      }
    }, false);
  }
  else {
    console.warn("Can’t find Table of Contents. Please use <nav id='toc'> around the ToC.");
  }

  /* Wrap tables in case they overflow */
  var tables = document.querySelectorAll(':not(.overlarge) > table.data, :not(.overlarge) > table.index');
  var numTables = tables.length;
  for (var i = 0; i < numTables; i++) {
    var table = tables[i];
    var wrapper = document.createElement('div');
    wrapper.className = 'overlarge';
    table.parentNode.insertBefore(wrapper, table);
    wrapper.appendChild(table);
  }

})();
</script>
  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
  <dl>
   <dt id="biblio-p1928r7">[P1928R7]
   <dd>Matthias Kretz. <a href="https://wg21.link/p1928r7"><cite>std::simd - Merge data-parallel types from the Parallelism TS 2</cite></a>. 15 October 2023. URL: <a href="https://wg21.link/p1928r7">https://wg21.link/p1928r7</a>
  </dl>