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PR libstdc++/80137 use std::nextafter instead of looping 

PR libstdc++/80137
	* include/bits/random.tcc (generate_canonical): Use std::nextafter
	or numeric_limits::epsilon() to reduce out-of-range values.
	* testsuite/26_numerics/random/uniform_real_distribution/operators/
	64351.cc: Verify complexity requirement is met.

From-SVN: r246542
This commit is contained in:
Jonathan Wakely 2017-03-28 17:09:49 +01:00 committed by Jonathan Wakely
parent 9d384e80bd
commit 92d85953a5
3 changed files with 33 additions and 14 deletions
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6
libstdc++-v3/ChangeLog
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@ -1,5 +1,11 @@
2017-03-28 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/80137
* include/bits/random.tcc (generate_canonical): Use std::nextafter
or numeric_limits::epsilon() to reduce out-of-range values.
* testsuite/26_numerics/random/uniform_real_distribution/operators/
64351.cc: Verify complexity requirement is met.
* doc/xml/manual/abi.xml: Add xml:id anchor.
* doc/xml/manual/using.xml (manual.intro.using.macros): Document
_GLIBCXX_RELEASE. Link to new anchor for __GLIBCXX__ notes.

25
libstdc++-v3/include/bits/random.tcc
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@ -3323,18 +3323,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
const size_t __m = std::max<size_t>(1UL,
(__b + __log2r - 1UL) / __log2r);
_RealType __ret;
do
_RealType __sum = _RealType(0);
_RealType __tmp = _RealType(1);
for (size_t __k = __m; __k != 0; --__k)
{
_RealType __sum = _RealType(0);
_RealType __tmp = _RealType(1);
for (size_t __k = __m; __k != 0; --__k)
{
__sum += _RealType(__urng() - __urng.min()) * __tmp;
__tmp *= __r;
}
__ret = __sum / __tmp;
__sum += _RealType(__urng() - __urng.min()) * __tmp;
__tmp *= __r;
}
__ret = __sum / __tmp;
if (__builtin_expect(__ret >= _RealType(1), 0))
{
#if _GLIBCXX_USE_C99_MATH_TR1
__ret = std::nextafter(_RealType(1), _RealType(0));
#else
__ret = _RealType(1)
- std::numeric_limits<_RealType>::epsilon() / _RealType(2);
#endif
}
while (__builtin_expect(__ret >= _RealType(1), 0));
return __ret;
}

16
libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/64351.cc
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@ -42,10 +42,18 @@ test02()
std::mt19937 rng(8890);
std::seed_seq sequence{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
rng.seed(sequence);
rng.discard(12 * 629143 + 6);
float n =
std::generate_canonical<float, std::numeric_limits<float>::digits>(rng);
VERIFY( n != 1.f );
rng.discard(12 * 629143);
std::mt19937 rng2{rng};
for (int i = 0; i < 20; ++i)
{
float n =
std::generate_canonical<float, std::numeric_limits<float>::digits>(rng);
VERIFY( n != 1.f );
// PR libstdc++/80137
rng2.discard(1);
VERIFY( rng == rng2 );
}
}
int