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libstdc++: Change return type of std::bit_width to int (LWG 3656)

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libstdc++-v3/ChangeLog:

	* doc/html/manual/bugs.html: Regenerate.
	* doc/xml/manual/intro.xml: Document LWG 3656 change.
	* include/std/bit (__bit_width, bit_width): Return int.
	* testsuite/26_numerics/bit/bit.pow.two/lwg3656.cc: New test.
This commit is contained in:
Jonathan Wakely 2022-11-24 21:36:07 +00:00
parent 3892251498
commit 4581328022
4 changed files with 30 additions and 2 deletions
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4
libstdc++-v3/doc/html/manual/bugs.html
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@ -619,4 +619,8 @@
<span class="bold"><strong><code class="code">path::lexically_relative</code> is confused by trailing slashes
</strong></span>
</span></dt><dd><p>Implement the fix for trailing slashes.
</p></dd><dt><a id="manual.bugs.dr3656"></a><span class="term"><a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#3656" target="_top">3656</a>:
<span class="bold"><strong>Inconsistent bit operations returning a count
</strong></span>
</span></dt><dd><p>Changed <code class="code">bit_width</code> to return <code class="code">int</code>.
</p></dd></dl></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="license.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="status.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="setup.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">License </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 2. Setup</td></tr></table></div></body></html>

7
libstdc++-v3/doc/xml/manual/intro.xml
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@ -1308,6 +1308,13 @@ requirements of the license of GCC.
<listitem><para>Implement the fix for trailing slashes.
</para></listitem></varlistentry>
<varlistentry xml:id="manual.bugs.dr3656"><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="&DR;#3656">3656</link>:
<emphasis role="bold">Inconsistent bit operations returning a count
</emphasis>
</term>
<listitem><para>Changed <code>bit_width</code> to return <code>int</code>.
</para></listitem></varlistentry>
</variablelist>
</section>

6
libstdc++-v3/include/std/bit
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@ -361,7 +361,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
template<typename _Tp>
constexpr _Tp
constexpr int
__bit_width(_Tp __x) noexcept
{
constexpr auto _Nd = __gnu_cxx::__int_traits<_Tp>::__digits;
@ -448,9 +448,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
bit_floor(_Tp __x) noexcept
{ return std::__bit_floor(__x); }
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3656. Inconsistent bit operations returning a count
/// The smallest integer greater than the base-2 logarithm of `x`.
template<typename _Tp>
constexpr _If_is_unsigned_integer<_Tp>
constexpr _If_is_unsigned_integer<_Tp, int>
bit_width(_Tp __x) noexcept
{ return std::__bit_width(__x); }

15
libstdc++-v3/testsuite/26_numerics/bit/bit.pow.two/lwg3656.cc Normal file
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@ -0,0 +1,15 @@
// { dg-options "-std=gnu++20" }
// { dg-do compile { target c++20 } }
#include <bit>
template<typename T> constexpr bool is_int = false;
template<> constexpr bool is_int<int> = true;
// LWG 3656. Inconsistent bit operations returning a count
// Rturn type of std::bit_width(T) changed from T to int.
static_assert( is_int<decltype(std::bit_width(1u))> );
static_assert( is_int<decltype(std::bit_width(1ul))> );
static_assert( is_int<decltype(std::bit_width(1ull))> );
static_assert( is_int<decltype(std::bit_width((unsigned short)1))> );
static_assert( is_int<decltype(std::bit_width((unsigned char)1))> );