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1//===-- Common header for helpers to set exceptional values -----*- 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_EXCEPT_VALUE_UTILS_H10#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_EXCEPT_VALUE_UTILS_H11 12#include "FEnvImpl.h"13#include "FPBits.h"14#include "cast.h"15#include "rounding_mode.h"16#include "src/__support/CPP/optional.h"17#include "src/__support/macros/config.h"18#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY19#include "src/__support/macros/properties/cpu_features.h"20#include "src/__support/macros/properties/types.h"21 22namespace LIBC_NAMESPACE_DECL {23 24namespace fputil {25 26// This file contains utility functions and classes to manage exceptional values27// when there are many of them.28//29// Example usage:30//31// Define list of exceptional inputs and outputs:32// static constexpr int N = ...; // Number of exceptional values.33// static constexpr fputil::ExceptValues<StorageType, N> Excepts {34// <list of input bits, output bits and offsets>35// };36//37// Check for exceptional inputs:38// if (auto r = Excepts.lookup(x_bits); LIBC_UNLIKELY(r.has_value()))39// return r.value();40 41template <typename T, size_t N> struct ExceptValues {42 static_assert(cpp::is_floating_point_v<T>, "Must be a floating point type.");43 44 using StorageType = typename FPBits<T>::StorageType;45 46 struct Mapping {47 StorageType input;48 StorageType rnd_towardzero_result;49 StorageType rnd_upward_offset;50 StorageType rnd_downward_offset;51 StorageType rnd_tonearest_offset;52 };53 54 Mapping values[N];55 56 LIBC_INLINE constexpr cpp::optional<T> lookup(StorageType x_bits) const {57 for (size_t i = 0; i < N; ++i) {58 if (LIBC_UNLIKELY(x_bits == values[i].input)) {59 StorageType out_bits = values[i].rnd_towardzero_result;60 switch (fputil::quick_get_round()) {61 case FE_UPWARD:62 out_bits += values[i].rnd_upward_offset;63 break;64 case FE_DOWNWARD:65 out_bits += values[i].rnd_downward_offset;66 break;67 case FE_TONEAREST:68 out_bits += values[i].rnd_tonearest_offset;69 break;70 }71 return FPBits<T>(out_bits).get_val();72 }73 }74 return cpp::nullopt;75 }76 77 LIBC_INLINE constexpr cpp::optional<T> lookup_odd(StorageType x_abs,78 bool sign) const {79 for (size_t i = 0; i < N; ++i) {80 if (LIBC_UNLIKELY(x_abs == values[i].input)) {81 StorageType out_bits = values[i].rnd_towardzero_result;82 switch (fputil::quick_get_round()) {83 case FE_UPWARD:84 if (sign)85 out_bits += values[i].rnd_downward_offset;86 else87 out_bits += values[i].rnd_upward_offset;88 break;89 case FE_DOWNWARD:90 // Use conditionals instead of ternary operator to work around gcc's91 // -Wconversion false positive bug:92 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10153793 if (sign)94 out_bits += values[i].rnd_upward_offset;95 else96 out_bits += values[i].rnd_downward_offset;97 break;98 case FE_TONEAREST:99 out_bits += values[i].rnd_tonearest_offset;100 break;101 }102 T result = FPBits<T>(out_bits).get_val();103 if (sign)104 result = -result;105 106 return result;107 }108 }109 return cpp::nullopt;110 }111};112 113// Helper functions to set results for exceptional cases.114template <typename T> LIBC_INLINE T round_result_slightly_down(T value_rn) {115 volatile T tmp = value_rn;116 tmp -= FPBits<T>::min_normal().get_val();117 return tmp;118}119 120template <typename T> LIBC_INLINE T round_result_slightly_up(T value_rn) {121 volatile T tmp = value_rn;122 tmp += FPBits<T>::min_normal().get_val();123 return tmp;124}125 126#if defined(LIBC_TYPES_HAS_FLOAT16) && \127 !defined(LIBC_TARGET_CPU_HAS_FAST_FLOAT16_OPS)128template <> LIBC_INLINE float16 round_result_slightly_down(float16 value_rn) {129 volatile float tmp = value_rn;130 tmp -= FPBits<float16>::min_normal().get_val();131 return cast<float16>(tmp);132}133 134template <> LIBC_INLINE float16 round_result_slightly_up(float16 value_rn) {135 volatile float tmp = value_rn;136 tmp += FPBits<float16>::min_normal().get_val();137 return cast<float16>(tmp);138}139#endif140 141} // namespace fputil142 143} // namespace LIBC_NAMESPACE_DECL144 145#endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_EXCEPT_VALUE_UTILS_H146