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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-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 "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_UNLIKELY |
19 | #include "src/__support/macros/properties/cpu_features.h" |
20 | #include "src/__support/macros/properties/types.h" |
21 | |
22 | namespace LIBC_NAMESPACE_DECL { |
23 | |
24 | namespace fputil { |
25 | |
26 | // This file contains utility functions and classes to manage exceptional values |
27 | // 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 | |
41 | template <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 | else |
87 | out_bits += values[i].rnd_upward_offset; |
88 | break; |
89 | case FE_DOWNWARD: |
90 | // Use conditionals instead of ternary operator to work around gcc's |
91 | // -Wconversion false positive bug: |
92 | // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101537 |
93 | if (sign) |
94 | out_bits += values[i].rnd_upward_offset; |
95 | else |
96 | 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. |
114 | template <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 | |
120 | template <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) |
128 | template <> 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 | |
134 | template <> 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 | #endif |
140 | |
141 | } // namespace fputil |
142 | |
143 | } // namespace LIBC_NAMESPACE_DECL |
144 | |
145 | #endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_EXCEPT_VALUE_UTILS_H |
146 |
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