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-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef LLVM_LIBC_SRC___SUPPORT_FPUTIL_EXCEPT_VALUE_UTILS_H
10#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_EXCEPT_VALUE_UTILS_H
11
12#include "FEnvImpl.h"
13#include "FPBits.h"
14#include "rounding_mode.h"
15#include "src/__support/CPP/optional.h"
16#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
17
18namespace LIBC_NAMESPACE {
19
20namespace fputil {
21
22// This file contains utility functions and classes to manage exceptional values
23// when there are many of them.
24//
25// Example usage:
26//
27// Define list of exceptional inputs and outputs:
28// static constexpr int N = ...; // Number of exceptional values.
29// static constexpr fputil::ExceptValues<StorageType, N> Excepts {
30// <list of input bits, output bits and offsets>
31// };
32//
33// Check for exceptional inputs:
34// if (auto r = Excepts.lookup(x_bits); LIBC_UNLIKELY(r.has_value()))
35// return r.value();
36
37template <typename T, size_t N> struct ExceptValues {
38 static_assert(cpp::is_floating_point_v<T>, "Must be a floating point type.");
39
40 using StorageType = typename FPBits<T>::StorageType;
41
42 struct Mapping {
43 StorageType input;
44 StorageType rnd_towardzero_result;
45 StorageType rnd_upward_offset;
46 StorageType rnd_downward_offset;
47 StorageType rnd_tonearest_offset;
48 };
49
50 Mapping values[N];
51
52 LIBC_INLINE constexpr cpp::optional<T> lookup(StorageType x_bits) const {
53 for (size_t i = 0; i < N; ++i) {
54 if (LIBC_UNLIKELY(x_bits == values[i].input)) {
55 StorageType out_bits = values[i].rnd_towardzero_result;
56 switch (fputil::quick_get_round()) {
57 case FE_UPWARD:
58 out_bits += values[i].rnd_upward_offset;
59 break;
60 case FE_DOWNWARD:
61 out_bits += values[i].rnd_downward_offset;
62 break;
63 case FE_TONEAREST:
64 out_bits += values[i].rnd_tonearest_offset;
65 break;
66 }
67 return FPBits<T>(out_bits).get_val();
68 }
69 }
70 return cpp::nullopt;
71 }
72
73 LIBC_INLINE constexpr cpp::optional<T> lookup_odd(StorageType x_abs,
74 bool sign) const {
75 for (size_t i = 0; i < N; ++i) {
76 if (LIBC_UNLIKELY(x_abs == values[i].input)) {
77 StorageType out_bits = values[i].rnd_towardzero_result;
78 switch (fputil::quick_get_round()) {
79 case FE_UPWARD:
80 out_bits += sign ? values[i].rnd_downward_offset
81 : values[i].rnd_upward_offset;
82 break;
83 case FE_DOWNWARD:
84 out_bits += sign ? values[i].rnd_upward_offset
85 : values[i].rnd_downward_offset;
86 break;
87 case FE_TONEAREST:
88 out_bits += values[i].rnd_tonearest_offset;
89 break;
90 }
91 T result = FPBits<T>(out_bits).get_val();
92 if (sign)
93 result = -result;
94
95 return result;
96 }
97 }
98 return cpp::nullopt;
99 }
100};
101
102// Helper functions to set results for exceptional cases.
103template <typename T> LIBC_INLINE T round_result_slightly_down(T value_rn) {
104 volatile T tmp = value_rn;
105 tmp -= FPBits<T>::min_normal().get_val();
106 return tmp;
107}
108
109template <typename T> LIBC_INLINE T round_result_slightly_up(T value_rn) {
110 volatile T tmp = value_rn;
111 tmp += FPBits<T>::min_normal().get_val();
112 return tmp;
113}
114
115} // namespace fputil
116
117} // namespace LIBC_NAMESPACE
118
119#endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_EXCEPT_VALUE_UTILS_H
120

source code of libc/src/__support/FPUtil/except_value_utils.h