For gcc-6 I fixed a bug in generate_canonical that allowed it to
return a value outside the permitted range (due to rounding), but that
was done by looping until we got a value that was in range, which
violates the complexity requirements.
John Salmon suggested a better fix in bugzilla, which is what is used
here.
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.
Tested powerpc64le-linux, committed to trunk.
This needs to be backported to gcc-6-branch too.
commit 611ce493bb4d47c153ef8b07721433f9d62dfe0d
Author: redi <redi@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Tue Mar 28 16:09:49 2017 +0000
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.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@246542
138bc75d-0d04-0410-961f-82ee72b054a4
diff --git a/libstdc++-v3/include/bits/random.tcc
b/libstdc++-v3/include/bits/random.tcc
index 2d5582a..df05ebe 100644
--- a/libstdc++-v3/include/bits/random.tcc
+++ b/libstdc++-v3/include/bits/random.tcc
@@ -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;
}
diff --git
a/libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/64351.cc
b/libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/64351.cc
index ddb67e8..229fe9c 100644
---
a/libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/64351.cc
+++
b/libstdc++-v3/testsuite/26_numerics/random/uniform_real_distribution/operators/64351.cc
@@ -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
