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<title>Issue 357: &lt;cmath&gt; float functions cannot return HUGE_VAL</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#NAD_Editorial">NAD Editorial</a> status.</em></p>
<h3 id="357"><a href="lwg-closed.html#357">357</a>. &lt;cmath&gt; float functions cannot return HUGE_VAL</h3>
<p><b>Section:</b> 29.7 <a href="https://wg21.link/c.math">[c.math]</a> <b>Status:</b> <a href="lwg-active.html#NAD_Editorial">NAD Editorial</a>
 <b>Submitter:</b> Ray Lischner <b>Opened:</b> 2002-02-26 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#c.math">issues</a> in [c.math].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The float versions of the math functions have no meaningful value to return 
for a range error. The long double versions have a value they can return, 
but it isn't necessarily the most reasonable value.
</p>

<p>
Section 26.5 [lib.c.math], paragraph 5, says that C++ "adds float and long 
double overloaded versions of these functions, with the same semantics," 
referring to the math functions from the C90 standard.
</p>

<p>
The C90 standard, in section 7.5.1, paragraph 3, says that functions return 
"the value of the macro HUGE_VAL" when they encounter a range error. 
Section 7.5, paragraph 2, defines HUGE_VAL as a macro that "expands to a 
positive double expression, not necessarily representable as a float."
</p>

<p>
Therefore, the float versions of the math functions have no way to
signal a range error. <i>[Cura&ccedil;ao: The LWG notes that this isn't
strictly correct, since errno is set.]</i> The semantics require that they
return HUGE_VAL, but they cannot because HUGE_VAL might not be
representable as a float.
</p>

<p>
The problem with long double functions is less severe because HUGE_VAL is 
representable as a long double. On the other hand, it might not be a "huge" 
long double value, and might fall well within the range of normal return 
values for a long double function. Therefore, it does not make sense for a 
long double function to return a double (HUGE_VAL) for a range error.
</p>


<p id="res-357"><b>Proposed resolution:</b></p>
<p>Cura&ccedil;ao: C99 was faced with a similar problem, which they fixed by
adding HUGE_VALF and HUGE_VALL in addition to HUGE_VAL.</p>

<p>C++ must also fix, but it should be done in the context of the
general C99 based changes to C++, not via DR. Thus the LWG in Cura&ccedil;ao
felt the resolution should be NAD, FUTURE, but the issue is being held
open for one more meeting to ensure LWG members not present during the
discussion concur.</p>


<p><b>Rationale:</b></p>
<p>Will be fixed as part of more general work in the TR.</p>





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