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<title>Issue 785: [tr1] Random Number Requirements in TR1</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">NAD</a> status.</em></p>
<h3 id="785"><a href="lwg-closed.html#785">785</a>. [tr1] Random Number Requirements in TR1</h3>
<p><b>Section:</b> 5.1.4.5 [tr1::tr.rand.eng.disc], 5.1.4.6 [tr1::tr.rand.eng.xor] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> John Maddock <b>Opened:</b> 2008-01-15 <b>Last modified:</b> 2016-02-01</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Table 16 of TR1 requires that all Pseudo Random Number generators have a
</p>

<blockquote><pre>
seed(integer-type s)
</pre></blockquote>

<p>
member function that is equivalent to:
</p>

<blockquote><pre>
mygen = Generator(s)
</pre></blockquote>

<p>
But the generators <code>xor_combine</code> and <code>discard_block</code> have no such seed member, only the
</p>

<blockquote><pre>
template &lt;class Gen&gt;
seed(Gen&amp;);
</pre></blockquote>

<p>
member, which will not accept an integer literal as an argument: something that appears to violate the intent of Table 16.
</p>

<p>
So... is this a bug in TR1?
</p>

<p>
This is a real issue BTW, since the Boost implementation does adhere to the requirements of Table 16, while at least one commercial implementation does not and follows a strict adherence to sections 5.1.4.5 and 5.1.4.6 instead.
</p>

<p><i>[
Jens adds:
]</i></p>


<blockquote><p>
Both engines do have the necessary
constructor, therefore the omission of the <code>seed()</code> member
functions appears to be an oversight.
</p></blockquote>

<p><i>[
Post Summit Daniel adds:
]</i></p>


<blockquote><p>
Recommend NAD: <code>xor_combine</code> does no longer exist and <code>discard_block[_engine]</code>
has now the required seed overload accepting a <code>result_type</code>, which shall be an
unsigned integral type.
</p></blockquote>

<p><i>[
Batavia (2009-05):
]</i></p>

<blockquote><p>
Move to NAD as recommended.
</p></blockquote>


<p id="res-785"><b>Proposed resolution:</b></p>
<p>
NAD Recommended.
</p>





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