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1//===---- Free-standing function to detect rounding mode --------*- C++ -*-===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef LLVM_LIBC_SRC___SUPPORT_FPUTIL_ROUNDING_MODE_H10#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_ROUNDING_MODE_H11 12#include "hdr/fenv_macros.h"13#include "src/__support/CPP/type_traits.h" // is_constant_evaluated14#include "src/__support/macros/attributes.h" // LIBC_INLINE15#include "src/__support/macros/config.h"16 17namespace LIBC_NAMESPACE_DECL {18namespace fputil {19 20namespace generic {21 22// Quick free-standing test whether fegetround() == FE_UPWARD.23// Using the following observation:24// 1.0f + 2^-25 = 1.0f for FE_TONEAREST, FE_DOWNWARD, FE_TOWARDZERO25// = 0x1.000002f for FE_UPWARD.26LIBC_INLINE bool fenv_is_round_up() {27 static volatile float x = 0x1.0p-25f;28 return (1.0f + x != 1.0f);29}30 31// Quick free-standing test whether fegetround() == FE_DOWNWARD.32// Using the following observation:33// -1.0f - 2^-25 = -1.0f for FE_TONEAREST, FE_UPWARD, FE_TOWARDZERO34// = -0x1.000002f for FE_DOWNWARD.35LIBC_INLINE bool fenv_is_round_down() {36 static volatile float x = 0x1.0p-25f;37 return (-1.0f - x != -1.0f);38}39 40// Quick free-standing test whether fegetround() == FE_TONEAREST.41// Using the following observation:42// 1.5f + 2^-24 = 1.5f for FE_TONEAREST, FE_DOWNWARD, FE_TOWARDZERO43// = 0x1.100002p0f for FE_UPWARD,44// 1.5f - 2^-24 = 1.5f for FE_TONEAREST, FE_UPWARD45// = 0x1.0ffffep-1f for FE_DOWNWARD, FE_TOWARDZERO46LIBC_INLINE bool fenv_is_round_to_nearest() {47 static volatile float x = 0x1.0p-24f;48 float y = 1.5f + x;49 return (y == 1.5f - x);50}51 52// Quick free-standing test whether fegetround() == FE_TOWARDZERO.53// Using the following observation:54// 1.0f + 2^-23 + 2^-24 = 0x1.000002p0f for FE_DOWNWARD, FE_TOWARDZERO55// = 0x1.000004p0f for FE_TONEAREST, FE_UPWARD,56// -1.0f - 2^-24 = -1.0f for FE_TONEAREST, FE_UPWARD, FE_TOWARDZERO57// = -0x1.000002p0f for FE_DOWNWARD58// So:59// (0x1.000002p0f + 2^-24) + (-1.0f - 2^-24) = 2^-23 for FE_TOWARDZERO60// = 2^-22 for FE_TONEAREST, FE_UPWARD61// = 0 for FE_DOWNWARD62LIBC_INLINE bool fenv_is_round_to_zero() {63 static volatile float x = 0x1.0p-24f;64 float y = x;65 return ((0x1.000002p0f + y) + (-1.0f - y) == 0x1.0p-23f);66}67 68// Quick free standing get rounding mode based on the above observations.69LIBC_INLINE int quick_get_round() {70 static volatile float x = 0x1.0p-24f;71 float y = x;72 float z = (0x1.000002p0f + y) + (-1.0f - y);73 74 if (z == 0.0f)75 return FE_DOWNWARD;76 if (z == 0x1.0p-23f)77 return FE_TOWARDZERO;78 return (2.0f + y == 2.0f) ? FE_TONEAREST : FE_UPWARD;79}80 81} // namespace generic82 83LIBC_INLINE static constexpr bool fenv_is_round_up() {84 if (cpp::is_constant_evaluated()) {85 return false;86 } else {87 return generic::fenv_is_round_up();88 }89}90 91LIBC_INLINE static constexpr bool fenv_is_round_down() {92 if (cpp::is_constant_evaluated()) {93 return false;94 } else {95 return generic::fenv_is_round_down();96 }97}98 99LIBC_INLINE static constexpr bool fenv_is_round_to_nearest() {100 if (cpp::is_constant_evaluated()) {101 return true;102 } else {103 return generic::fenv_is_round_to_nearest();104 }105}106 107LIBC_INLINE static constexpr bool fenv_is_round_to_zero() {108 if (cpp::is_constant_evaluated()) {109 return false;110 } else {111 return generic::fenv_is_round_to_zero();112 }113}114 115// Quick free standing get rounding mode based on the above observations.116LIBC_INLINE static constexpr int quick_get_round() {117 if (cpp::is_constant_evaluated()) {118 return FE_TONEAREST;119 } else {120 return generic::quick_get_round();121 }122}123 124} // namespace fputil125} // namespace LIBC_NAMESPACE_DECL126 127#endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_ROUNDING_MODE_H128