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Fix std::midpoint for denormal values

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* include/std/numeric (midpoint(T, T)): Change implementation for
	floating-point types to avoid incorrect rounding of denormals.
	* testsuite/26_numerics/midpoint/floating.cc: Add check for correct
	rounding with denormals.
	* testsuite/26_numerics/gcd/gcd_neg.cc: Adjust dg-error line numbers.
	* testsuite/26_numerics/lcm/lcm_neg.cc: Likewise.

From-SVN: r272616
This commit is contained in:
Jonathan Wakely 2019-06-24 13:09:51 +01:00 • committed by Jonathan Wakely
parent ff164b601b
commit a3c8d7fbe2
5 changed files with 52 additions and 17 deletions
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7
libstdc++-v3/ChangeLog
View file

@ -1,5 +1,12 @@
2019-06-24 Jonathan Wakely <jwakely@redhat.com>
* include/std/numeric (midpoint(T, T)): Change implementation for
floating-point types to avoid incorrect rounding of denormals.
* testsuite/26_numerics/midpoint/floating.cc: Add check for correct
rounding with denormals.
* testsuite/26_numerics/gcd/gcd_neg.cc: Adjust dg-error line numbers.
* testsuite/26_numerics/lcm/lcm_neg.cc: Likewise.
* testsuite/18_support/headers/cfloat/values_c++17.cc: New test.
2019-06-20 Jonathan Wakely <jwakely@redhat.com>

36
libstdc++-v3/include/std/numeric
View file

@ -69,9 +69,8 @@
* @defgroup numerics Numerics
*
* Components for performing numeric operations. Includes support for
* for complex number types, random number generation, numeric
* (n-at-a-time) arrays, generalized numeric algorithms, and special
* math functions.
* complex number types, random number generation, numeric (n-at-a-time)
* arrays, generalized numeric algorithms, and mathematical special functions.
*/
#if __cplusplus >= 201402L
@ -156,11 +155,22 @@ namespace __detail
#endif // C++17
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // C++14
#if __cplusplus > 201703L
#include <limits>
#include <bits/std_abs.h>
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
// midpoint
# define __cpp_lib_interpolate 201902L
template<typename _Tp>
template<typename _Tp>
constexpr
enable_if_t<__and_v<is_arithmetic<_Tp>, is_same<remove_cv_t<_Tp>, _Tp>,
__not_<is_same<_Tp, bool>>>,
@ -182,11 +192,17 @@ template<typename _Tp>
}
return __a + __k * _Tp(_Up(__M - __m) / 2);
}
else
else // is_floating
{
return __builtin_isnormal(__a) && __builtin_isnormal(__b)
? __a / 2 + __b / 2
: (__a + __b) / 2;
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]]
return (__a + __b) / 2; // always correctly rounded
if (std::abs(__a) < __lo) // not safe to halve __a
return __a + __b/2;
if (std::abs(__b) < __lo) // not safe to halve __b
return __a/2 + __b;
return __a/2 + __b/2; // otherwise correctly rounded
}
}
@ -197,12 +213,10 @@ template<typename _Tp>
{
return __a + (__b - __a) / 2;
}
#endif // C++20
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // C++14
#endif // C++20
#if __cplusplus > 201402L
#include <bits/stl_function.h>

6
libstdc++-v3/testsuite/26_numerics/gcd/gcd_neg.cc
View file

@ -46,9 +46,9 @@ test01()
std::gcd<const int&, const int&>(0.1, 0.1); // { dg-error "from here" }
}
// { dg-error "integers" "" { target *-*-* } 133 }
// { dg-error "integers" "" { target *-*-* } 134 }
// { dg-error "integers" "" { target *-*-* } 135 }
// { dg-error "not bools" "" { target *-*-* } 136 }
// { dg-error "not bools" "" { target *-*-* } 138 }
// { dg-error "not bools" "" { target *-*-* } 135 }
// { dg-error "not bools" "" { target *-*-* } 137 }
// { dg-prune-output "deleted function" }
// { dg-prune-output "invalid operands" }

6
libstdc++-v3/testsuite/26_numerics/lcm/lcm_neg.cc
View file

@ -46,9 +46,9 @@ test01()
std::lcm<const int&, const int&>(0.1, 0.1); // { dg-error "from here" }
}
// { dg-error "integers" "" { target *-*-* } 147 }
// { dg-error "integers" "" { target *-*-* } 148 }
// { dg-error "integers" "" { target *-*-* } 149 }
// { dg-error "not bools" "" { target *-*-* } 150 }
// { dg-error "not bools" "" { target *-*-* } 152 }
// { dg-error "not bools" "" { target *-*-* } 149 }
// { dg-error "not bools" "" { target *-*-* } 151 }
// { dg-prune-output "deleted function" }
// { dg-prune-output "invalid operands" }

14
libstdc++-v3/testsuite/26_numerics/midpoint/floating.cc
View file

@ -20,6 +20,7 @@
#include <numeric>
#include <limits>
#include <cfloat>
#include <testsuite_hooks.h>
void
@ -57,6 +58,19 @@ test03()
VERIFY( std::midpoint(9e9l, -9e9l) == 0.0l );
}
namespace test04
{
// https://gcc.gnu.org/ml/libstdc++/2019-03/msg00065.html
constexpr double d = DBL_MIN + DBL_TRUE_MIN;
static_assert( std::midpoint(d, d) == d );
constexpr float f = FLT_MIN + FLT_TRUE_MIN;
static_assert( std::midpoint(f, f) == f );
constexpr long double l = LDBL_MIN + LDBL_TRUE_MIN;
static_assert( std::midpoint(l, l) == l );
}
int main()
{
test01();