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Revert "[libc++][math] Fix undue overflowing of std::hypot(x,y,z) (#…
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…93350)"

Summary:
This reverts commit 9628777.

More details in #93350, but
this broke the PowerPC sanitizer bots.

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Differential Revision: https://phabricator.intern.facebook.com/D60250681
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@hctim @yuxuanchen1997
hctim authored and yuxuanchen1997 committed Jul 25, 2024
1 parent cd02bd9 commit 3692866
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89 changes: 0 additions & 89 deletions libcxx/include/__math/hypot.h
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Expand Up @@ -15,21 +15,10 @@
#include <__type_traits/is_same.h>
#include <__type_traits/promote.h>

#if _LIBCPP_STD_VER >= 17
# include <__algorithm/max.h>
# include <__math/abs.h>
# include <__math/roots.h>
# include <__utility/pair.h>
# include <limits>
#endif

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD

namespace __math {
Expand All @@ -52,86 +41,8 @@ inline _LIBCPP_HIDE_FROM_ABI typename __promote<_A1, _A2>::type hypot(_A1 __x, _
return __math::hypot((__result_type)__x, (__result_type)__y);
}

#if _LIBCPP_STD_VER >= 17
// Factors needed to determine if over-/underflow might happen for `std::hypot(x,y,z)`.
// returns [overflow_threshold, overflow_scale]
template <class _Real>
_LIBCPP_HIDE_FROM_ABI std::pair<_Real, _Real> __hypot_factors() {
static_assert(std::numeric_limits<_Real>::is_iec559);

if constexpr (std::is_same_v<_Real, float>) {
static_assert(-125 == std::numeric_limits<_Real>::min_exponent);
static_assert(+128 == std::numeric_limits<_Real>::max_exponent);
return {0x1.0p+62f, 0x1.0p-70f};
} else if constexpr (std::is_same_v<_Real, double>) {
static_assert(-1021 == std::numeric_limits<_Real>::min_exponent);
static_assert(+1024 == std::numeric_limits<_Real>::max_exponent);
return {0x1.0p+510, 0x1.0p-600};
} else { // long double
static_assert(std::is_same_v<_Real, long double>);

// preprocessor guard necessary, otherwise literals (e.g. `0x1.0p+8'190l`) throw warnings even when shielded by `if
// constexpr`
# if __DBL_MAX_EXP__ == __LDBL_MAX_EXP__
static_assert(sizeof(_Real) == sizeof(double));
return static_cast<std::pair<_Real, _Real>>(__math::__hypot_factors<double>());
# else
static_assert(sizeof(_Real) > sizeof(double));
static_assert(-16381 == std::numeric_limits<_Real>::min_exponent);
static_assert(+16384 == std::numeric_limits<_Real>::max_exponent);
return {0x1.0p+8190l, 0x1.0p-9000l};
# endif
}
}

// Computes the three-dimensional hypotenuse: `std::hypot(x,y,z)`.
// The naive implementation might over-/underflow which is why this implementation is more involved:
// If the square of an argument might run into issues, we scale the arguments appropriately.
// See https://github.com/llvm/llvm-project/issues/92782 for a detailed discussion and summary.
template <class _Real>
_LIBCPP_HIDE_FROM_ABI _Real __hypot(_Real __x, _Real __y, _Real __z) {
const _Real __max_abs = std::max(__math::fabs(__x), std::max(__math::fabs(__y), __math::fabs(__z)));
const auto [__overflow_threshold, __overflow_scale] = __math::__hypot_factors<_Real>();
_Real __scale;
if (__max_abs > __overflow_threshold) { // x*x + y*y + z*z might overflow
__scale = __overflow_scale;
__x *= __scale;
__y *= __scale;
__z *= __scale;
} else if (__max_abs < 1 / __overflow_threshold) { // x*x + y*y + z*z might underflow
__scale = 1 / __overflow_scale;
__x *= __scale;
__y *= __scale;
__z *= __scale;
} else
__scale = 1;
return __math::sqrt(__x * __x + __y * __y + __z * __z) / __scale;
}

inline _LIBCPP_HIDE_FROM_ABI float hypot(float __x, float __y, float __z) { return __math::__hypot(__x, __y, __z); }

inline _LIBCPP_HIDE_FROM_ABI double hypot(double __x, double __y, double __z) { return __math::__hypot(__x, __y, __z); }

inline _LIBCPP_HIDE_FROM_ABI long double hypot(long double __x, long double __y, long double __z) {
return __math::__hypot(__x, __y, __z);
}

template <class _A1,
class _A2,
class _A3,
std::enable_if_t< is_arithmetic_v<_A1> && is_arithmetic_v<_A2> && is_arithmetic_v<_A3>, int> = 0 >
_LIBCPP_HIDE_FROM_ABI typename __promote<_A1, _A2, _A3>::type hypot(_A1 __x, _A2 __y, _A3 __z) _NOEXCEPT {
using __result_type = typename __promote<_A1, _A2, _A3>::type;
static_assert(!(
std::is_same_v<_A1, __result_type> && std::is_same_v<_A2, __result_type> && std::is_same_v<_A3, __result_type>));
return __math::__hypot(
static_cast<__result_type>(__x), static_cast<__result_type>(__y), static_cast<__result_type>(__z));
}
#endif

} // namespace __math

_LIBCPP_END_NAMESPACE_STD
_LIBCPP_POP_MACROS

#endif // _LIBCPP___MATH_HYPOT_H
25 changes: 24 additions & 1 deletion libcxx/include/cmath
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Expand Up @@ -313,7 +313,6 @@ constexpr long double lerp(long double a, long double b, long double t) noexcept
*/

#include <__config>
#include <__math/hypot.h>
#include <__type_traits/enable_if.h>
#include <__type_traits/is_arithmetic.h>
#include <__type_traits/is_constant_evaluated.h>
Expand Down Expand Up @@ -554,6 +553,30 @@ using ::scalbnl _LIBCPP_USING_IF_EXISTS;
using ::tgammal _LIBCPP_USING_IF_EXISTS;
using ::truncl _LIBCPP_USING_IF_EXISTS;

#if _LIBCPP_STD_VER >= 17
inline _LIBCPP_HIDE_FROM_ABI float hypot(float __x, float __y, float __z) {
return sqrt(__x * __x + __y * __y + __z * __z);
}
inline _LIBCPP_HIDE_FROM_ABI double hypot(double __x, double __y, double __z) {
return sqrt(__x * __x + __y * __y + __z * __z);
}
inline _LIBCPP_HIDE_FROM_ABI long double hypot(long double __x, long double __y, long double __z) {
return sqrt(__x * __x + __y * __y + __z * __z);
}

template <class _A1, class _A2, class _A3>
inline _LIBCPP_HIDE_FROM_ABI
typename enable_if_t< is_arithmetic<_A1>::value && is_arithmetic<_A2>::value && is_arithmetic<_A3>::value,
__promote<_A1, _A2, _A3> >::type
hypot(_A1 __lcpp_x, _A2 __lcpp_y, _A3 __lcpp_z) _NOEXCEPT {
typedef typename __promote<_A1, _A2, _A3>::type __result_type;
static_assert(
!(is_same<_A1, __result_type>::value && is_same<_A2, __result_type>::value && is_same<_A3, __result_type>::value),
"");
return std::hypot((__result_type)__lcpp_x, (__result_type)__lcpp_y, (__result_type)__lcpp_z);
}
#endif

template <class _A1, __enable_if_t<is_floating_point<_A1>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bool __constexpr_isnan(_A1 __lcpp_x) _NOEXCEPT {
#if __has_builtin(__builtin_isnan)
Expand Down
3 changes: 0 additions & 3 deletions libcxx/test/libcxx/transitive_includes/cxx17.csv
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Expand Up @@ -130,9 +130,6 @@ chrono type_traits
chrono vector
chrono version
cinttypes cstdint
cmath cstddef
cmath cstdint
cmath initializer_list
cmath limits
cmath type_traits
cmath version
Expand Down
3 changes: 0 additions & 3 deletions libcxx/test/libcxx/transitive_includes/cxx20.csv
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Expand Up @@ -135,9 +135,6 @@ chrono type_traits
chrono vector
chrono version
cinttypes cstdint
cmath cstddef
cmath cstdint
cmath initializer_list
cmath limits
cmath type_traits
cmath version
Expand Down
3 changes: 0 additions & 3 deletions libcxx/test/libcxx/transitive_includes/cxx23.csv
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Expand Up @@ -83,9 +83,6 @@ chrono string_view
chrono vector
chrono version
cinttypes cstdint
cmath cstddef
cmath cstdint
cmath initializer_list
cmath limits
cmath version
codecvt cctype
Expand Down
3 changes: 0 additions & 3 deletions libcxx/test/libcxx/transitive_includes/cxx26.csv
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Original file line number Diff line number Diff line change
Expand Up @@ -83,9 +83,6 @@ chrono string_view
chrono vector
chrono version
cinttypes cstdint
cmath cstddef
cmath cstdint
cmath initializer_list
cmath limits
cmath version
codecvt cctype
Expand Down
91 changes: 16 additions & 75 deletions libcxx/test/std/numerics/c.math/cmath.pass.cpp
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Expand Up @@ -12,17 +12,14 @@

// <cmath>

#include <array>
#include <cmath>
#include <limits>
#include <type_traits>
#include <cassert>

#include "fp_compare.h"
#include "test_macros.h"
#include "hexfloat.h"
#include "truncate_fp.h"
#include "type_algorithms.h"

// convertible to int/float/double/etc
template <class T, int N=0>
Expand Down Expand Up @@ -1116,56 +1113,6 @@ void test_fmin()
assert(std::fmin(1,0) == 0);
}

#if TEST_STD_VER >= 17
struct TestHypot3 {
template <class Real>
void operator()() const {
const auto check = [](Real elem, Real abs_tol) {
assert(std::isfinite(std::hypot(elem, Real(0), Real(0))));
assert(fptest_close(std::hypot(elem, Real(0), Real(0)), elem, abs_tol));
assert(std::isfinite(std::hypot(elem, elem, Real(0))));
assert(fptest_close(std::hypot(elem, elem, Real(0)), std::sqrt(Real(2)) * elem, abs_tol));
assert(std::isfinite(std::hypot(elem, elem, elem)));
assert(fptest_close(std::hypot(elem, elem, elem), std::sqrt(Real(3)) * elem, abs_tol));
};

{ // check for overflow
const auto [elem, abs_tol] = []() -> std::array<Real, 2> {
if constexpr (std::is_same_v<Real, float>)
return {1e20f, 1e16f};
else if constexpr (std::is_same_v<Real, double>)
return {1e300, 1e287};
else { // long double
# if __DBL_MAX_EXP__ == __LDBL_MAX_EXP__
return {1e300l, 1e287l}; // 64-bit
# else
return {1e4000l, 1e3985l}; // 80- or 128-bit
# endif
}
}();
check(elem, abs_tol);
}

{ // check for underflow
const auto [elem, abs_tol] = []() -> std::array<Real, 2> {
if constexpr (std::is_same_v<Real, float>)
return {1e-20f, 1e-24f};
else if constexpr (std::is_same_v<Real, double>)
return {1e-287, 1e-300};
else { // long double
# if __DBL_MAX_EXP__ == __LDBL_MAX_EXP__
return {1e-287l, 1e-300l}; // 64-bit
# else
return {1e-3985l, 1e-4000l}; // 80- or 128-bit
# endif
}
}();
check(elem, abs_tol);
}
}
};
#endif

void test_hypot()
{
static_assert((std::is_same<decltype(std::hypot((float)0, (float)0)), float>::value), "");
Expand All @@ -1188,31 +1135,25 @@ void test_hypot()
static_assert((std::is_same<decltype(hypot(Ambiguous(), Ambiguous())), Ambiguous>::value), "");
assert(std::hypot(3,4) == 5);

#if TEST_STD_VER >= 17
// clang-format off
static_assert((std::is_same_v<decltype(std::hypot((float)0, (float)0, (float)0)), float>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (bool)0, (float)0)), double>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (unsigned short)0, (double)0)), double>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (int)0, (long double)0)), long double>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (double)0, (long)0)), double>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (long double)0, (unsigned long)0)), long double>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (int)0, (long long)0)), double>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (int)0, (unsigned long long)0)), double>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (double)0, (double)0)), double>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (long double)0, (long double)0)), long double>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (float)0, (double)0)), double>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (float)0, (long double)0)), long double>));
static_assert((std::is_same_v<decltype(std::hypot((float)0, (double)0, (long double)0)), long double>));
static_assert((std::is_same_v<decltype(std::hypot((int)0, (int)0, (int)0)), double>));
static_assert((std::is_same_v<decltype(hypot(Ambiguous(), Ambiguous(), Ambiguous())), Ambiguous>));
// clang-format on
#if TEST_STD_VER > 14
static_assert((std::is_same<decltype(std::hypot((float)0, (float)0, (float)0)), float>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (bool)0, (float)0)), double>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (unsigned short)0, (double)0)), double>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (int)0, (long double)0)), long double>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (double)0, (long)0)), double>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (long double)0, (unsigned long)0)), long double>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (int)0, (long long)0)), double>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (int)0, (unsigned long long)0)), double>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (double)0, (double)0)), double>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (long double)0, (long double)0)), long double>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (float)0, (double)0)), double>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (float)0, (long double)0)), long double>::value), "");
static_assert((std::is_same<decltype(std::hypot((float)0, (double)0, (long double)0)), long double>::value), "");
static_assert((std::is_same<decltype(std::hypot((int)0, (int)0, (int)0)), double>::value), "");
static_assert((std::is_same<decltype(hypot(Ambiguous(), Ambiguous(), Ambiguous())), Ambiguous>::value), "");

assert(std::hypot(2,3,6) == 7);
assert(std::hypot(1,4,8) == 9);

// Check for undue over-/underflows of intermediate results.
// See discussion at https://github.com/llvm/llvm-project/issues/92782.
types::for_each(types::floating_point_types(), TestHypot3());
#endif
}

Expand Down
45 changes: 25 additions & 20 deletions libcxx/test/support/fp_compare.h
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Original file line number Diff line number Diff line change
Expand Up @@ -9,34 +9,39 @@
#ifndef SUPPORT_FP_COMPARE_H
#define SUPPORT_FP_COMPARE_H

#include <cmath> // for std::abs
#include <algorithm> // for std::max
#include <cmath> // for std::abs
#include <algorithm> // for std::max
#include <cassert>
#include <__config>

// See https://www.boost.org/doc/libs/1_70_0/libs/test/doc/html/boost_test/testing_tools/extended_comparison/floating_point/floating_points_comparison_theory.html

template <typename T>
bool fptest_close(T val, T expected, T eps) {
_LIBCPP_CONSTEXPR T zero = T(0);
assert(eps >= zero);
template<typename T>
bool fptest_close(T val, T expected, T eps)
{
constexpr T zero = T(0);
assert(eps >= zero);

// Handle the zero cases
if (eps == zero)
return val == expected;
if (val == zero)
return std::abs(expected) <= eps;
if (expected == zero)
return std::abs(val) <= eps;
// Handle the zero cases
if (eps == zero) return val == expected;
if (val == zero) return std::abs(expected) <= eps;
if (expected == zero) return std::abs(val) <= eps;

return std::abs(val - expected) < eps && std::abs(val - expected) / std::abs(val) < eps;
return std::abs(val - expected) < eps
&& std::abs(val - expected)/std::abs(val) < eps;
}

template <typename T>
bool fptest_close_pct(T val, T expected, T percent) {
assert(percent >= T(0));
T eps = (percent / T(100)) * std::max(std::abs(val), std::abs(expected));
return fptest_close(val, expected, eps);
template<typename T>
bool fptest_close_pct(T val, T expected, T percent)
{
constexpr T zero = T(0);
assert(percent >= zero);

// Handle the zero cases
if (percent == zero) return val == expected;
T eps = (percent / T(100)) * std::max(std::abs(val), std::abs(expected));

return fptest_close(val, expected, eps);
}


#endif // SUPPORT_FP_COMPARE_H

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