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Fix non-portable use of std::abs(double) in constexpr function

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Although libstdc++ adds 'constexpr' to its std::abs(floating-point)
overloads (as a non-conforming extension), those overloads are not used
if the target libc provides them, which is the case on Solaris.

The fix is to avoid std::abs and simply apply the negation when needed.

	* include/std/numeric (midpoint(T, T)): Avoid std::abs in constexpr
	function.

From-SVN: r272653
This commit is contained in:
Jonathan Wakely 2019-06-25 14:18:36 +01:00 committed by Jonathan Wakely
parent 247b63e33d
commit e88d863cbd
2 changed files with 10 additions and 4 deletions
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5
libstdc++-v3/ChangeLog
View File

@ -1,3 +1,8 @@
2019-06-25 Jonathan Wakely <jwakely@redhat.com>
* include/std/numeric (midpoint(T, T)): Avoid std::abs in constexpr
function.
2019-06-25 Jakub Jelinek <jakub@redhat.com>
* include/pstl/pstl_config.h (_PSTL_PRAGMA_SIMD_SCAN,

9
libstdc++-v3/include/std/numeric
View File

@ -162,7 +162,6 @@ _GLIBCXX_END_NAMESPACE_VERSION
#if __cplusplus > 201703L
#include <limits>
#include <bits/std_abs.h>
namespace std _GLIBCXX_VISIBILITY(default)
{
@ -196,11 +195,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
constexpr _Tp __lo = numeric_limits<_Tp>::min() * 2;
constexpr _Tp __hi = numeric_limits<_Tp>::max() / 2;
if (std::abs(__a) <= __hi && std::abs(__b) <= __hi) [[likely]]
const _Tp __abs_a = __a < 0 ? -__a : __a;
const _Tp __abs_b = __b < 0 ? -__b : __b;
if (__abs_a <= __hi && __abs_b <= __hi) [[likely]]
return (__a + __b) / 2; // always correctly rounded
if (std::abs(__a) < __lo) // not safe to halve __a
if (__abs_a < __lo) // not safe to halve __a
return __a + __b/2;
if (std::abs(__b) < __lo) // not safe to halve __b
if (__abs_b < __lo) // not safe to halve __b
return __a/2 + __b;
return __a/2 + __b/2; // otherwise correctly rounded
}