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Fix the floating point version of midpoint. It wasn't constexpr, among other things. Add more tests. As a drive-by, the LCD implementation had a class named '__abs' which did a 'absolute value to a common-type' conversion. Rename that to be '__ct_abs'. 

llvm-svn: 363714
This commit is contained in:
Marshall Clow 2019-06-18 18:13:54 +00:00
parent 032b54f8e8
commit 8dc6840f1c
2 changed files with 34 additions and 16 deletions
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29
libcxx/include/numeric
View File

@ -460,10 +460,10 @@ iota(_ForwardIterator __first, _ForwardIterator __last, _Tp __value_)
#if _LIBCPP_STD_VER > 14
template <typename _Result, typename _Source, bool _IsSigned = is_signed<_Source>::value> struct __abs;
template <typename _Result, typename _Source, bool _IsSigned = is_signed<_Source>::value> struct __ct_abs;
template <typename _Result, typename _Source>
struct __abs<_Result, _Source, true> {
struct __ct_abs<_Result, _Source, true> {
_LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
_Result operator()(_Source __t) const noexcept
{
@ -474,7 +474,7 @@ struct __abs<_Result, _Source, true> {
};
template <typename _Result, typename _Source>
struct __abs<_Result, _Source, false> {
struct __ct_abs<_Result, _Source, false> {
_LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
_Result operator()(_Source __t) const noexcept { return __t; }
};
@ -500,8 +500,8 @@ gcd(_Tp __m, _Up __n)
using _Rp = common_type_t<_Tp,_Up>;
using _Wp = make_unsigned_t<_Rp>;
return static_cast<_Rp>(_VSTD::__gcd(
static_cast<_Wp>(__abs<_Rp, _Tp>()(__m)),
static_cast<_Wp>(__abs<_Rp, _Up>()(__n))));
static_cast<_Wp>(__ct_abs<_Rp, _Tp>()(__m)),
static_cast<_Wp>(__ct_abs<_Rp, _Up>()(__n))));
}
template<class _Tp, class _Up>
@ -516,8 +516,8 @@ lcm(_Tp __m, _Up __n)
return 0;
using _Rp = common_type_t<_Tp,_Up>;
_Rp __val1 = __abs<_Rp, _Tp>()(__m) / _VSTD::gcd(__m, __n);
_Rp __val2 = __abs<_Rp, _Up>()(__n);
_Rp __val1 = __ct_abs<_Rp, _Tp>()(__m) / _VSTD::gcd(__m, __n);
_Rp __val2 = __ct_abs<_Rp, _Up>()(__n);
_LIBCPP_ASSERT((numeric_limits<_Rp>::max() / __val1 > __val2), "Overflow in lcm");
return __val1 * __val2;
}
@ -563,16 +563,23 @@ constexpr int __sign(_Tp __val) {
return (_Tp(0) < __val) - (__val < _Tp(0));
}
template <typename _Fp>
constexpr _Fp __fp_abs(_Fp __f) { return __f >= 0 ? __f : -__f; }
template <class _Fp>
_LIBCPP_INLINE_VISIBILITY constexpr
enable_if_t<is_floating_point_v<_Fp>, _Fp>
midpoint(_Fp __a, _Fp __b) noexcept
{
return isnormal(__a) && isnormal(__b)
&& ((__sign(__a) != __sign(__b)) || ((numeric_limits<_Fp>::max() - abs(__a)) < abs(__b)))
? __a / 2 + __b / 2
: (__a + __b) / 2;
constexpr _Fp __lo = numeric_limits<_Fp>::min()*2;
constexpr _Fp __hi = numeric_limits<_Fp>::max()/2;
return __fp_abs(__a) <= __hi && __fp_abs(__b) <= __hi ? // typical case: overflow is impossible
(__a + __b)/2 : // always correctly rounded
__fp_abs(__a) < __lo ? __a + __b/2 : // not safe to halve a
__fp_abs(__a) < __lo ? __a/2 + __b : // not safe to halve b
__a/2 + __b/2; // otherwise correctly rounded
}
#endif // _LIBCPP_STD_VER > 17
_LIBCPP_END_NAMESPACE_STD

21
libcxx/test/std/numerics/numeric.ops/numeric.ops.midpoint/midpoint.float.pass.cpp
View File

@ -43,11 +43,11 @@ void fp_test()
constexpr T minV = std::numeric_limits<T>::min();
// Things that can be compared exactly
assert((std::midpoint(T(0), T(0)) == T(0)));
assert((std::midpoint(T(2), T(4)) == T(3)));
assert((std::midpoint(T(4), T(2)) == T(3)));
assert((std::midpoint(T(3), T(4)) == T(3.5)));
assert((std::midpoint(T(0), T(0.4)) == T(0.2)));
static_assert((std::midpoint(T(0), T(0)) == T(0)), "");
static_assert((std::midpoint(T(2), T(4)) == T(3)), "");
static_assert((std::midpoint(T(4), T(2)) == T(3)), "");
static_assert((std::midpoint(T(3), T(4)) == T(3.5)), "");
static_assert((std::midpoint(T(0), T(0.4)) == T(0.2)), "");
// Things that can't be compared exactly
constexpr T pct = fp_error_pct<T>();
@ -70,6 +70,17 @@ void fp_test()
assert((fptest_close_pct(std::midpoint(T(0), minV), minV/2, pct)));
assert((fptest_close_pct(std::midpoint(maxV, maxV), maxV, pct)));
assert((fptest_close_pct(std::midpoint(minV, minV), minV, pct)));
assert((fptest_close_pct(std::midpoint(maxV, minV), maxV/2, pct)));
assert((fptest_close_pct(std::midpoint(minV, maxV), maxV/2, pct)));
// Near the min and the max
assert((fptest_close_pct(std::midpoint(maxV*T(0.75), maxV*T(0.50)), maxV*T(0.625), pct)));
assert((fptest_close_pct(std::midpoint(maxV*T(0.50), maxV*T(0.75)), maxV*T(0.625), pct)));
assert((fptest_close_pct(std::midpoint(minV*T(2), minV*T(8)), minV*T(5), pct)));
// Big numbers of different signs
assert((fptest_close_pct(std::midpoint(maxV*T( 0.75), maxV*T(-0.5)), maxV*T( 0.125), pct)));
assert((fptest_close_pct(std::midpoint(maxV*T(-0.75), maxV*T( 0.5)), maxV*T(-0.125), pct)));
// Denormalized values
// TODO