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1//===-- Mimics llvm/Support/MathExtras.h ------------------------*- C++ -*-===//
2// Provides useful math functions.
3//
4// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5// See https://llvm.org/LICENSE.txt for license information.
6// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7//
8//===----------------------------------------------------------------------===//
9
10#ifndef LLVM_LIBC_SRC___SUPPORT_MATH_EXTRAS_H
11#define LLVM_LIBC_SRC___SUPPORT_MATH_EXTRAS_H
12
13#include "src/__support/CPP/bit.h" // countl_one, countr_zero
14#include "src/__support/CPP/limits.h" // CHAR_BIT, numeric_limits
15#include "src/__support/CPP/type_traits.h" // is_unsigned_v, is_constant_evaluated
16#include "src/__support/macros/attributes.h" // LIBC_INLINE
17#include "src/__support/macros/config.h"
18
19namespace LIBC_NAMESPACE_DECL {
20
21// Create a bitmask with the count right-most bits set to 1, and all other bits
22// set to 0. Only unsigned types are allowed.
23template <typename T, size_t count>
24LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
25mask_trailing_ones() {
26 constexpr unsigned T_BITS = CHAR_BIT * sizeof(T);
27 static_assert(count <= T_BITS && "Invalid bit index");
28 return count == 0 ? 0 : (T(-1) >> (T_BITS - count));
29}
30
31// Create a bitmask with the count left-most bits set to 1, and all other bits
32// set to 0. Only unsigned types are allowed.
33template <typename T, size_t count>
34LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
35mask_leading_ones() {
36 return T(~mask_trailing_ones<T, CHAR_BIT * sizeof(T) - count>());
37}
38
39// Create a bitmask with the count right-most bits set to 0, and all other bits
40// set to 1. Only unsigned types are allowed.
41template <typename T, size_t count>
42LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
43mask_trailing_zeros() {
44 return mask_leading_ones<T, CHAR_BIT * sizeof(T) - count>();
45}
46
47// Create a bitmask with the count left-most bits set to 0, and all other bits
48// set to 1. Only unsigned types are allowed.
49template <typename T, size_t count>
50LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
51mask_leading_zeros() {
52 return mask_trailing_ones<T, CHAR_BIT * sizeof(T) - count>();
53}
54
55// Returns whether 'a + b' overflows, the result is stored in 'res'.
56template <typename T>
57[[nodiscard]] LIBC_INLINE constexpr bool add_overflow(T a, T b, T &res) {
58 return __builtin_add_overflow(a, b, &res);
59}
60
61// Returns whether 'a - b' overflows, the result is stored in 'res'.
62template <typename T>
63[[nodiscard]] LIBC_INLINE constexpr bool sub_overflow(T a, T b, T &res) {
64 return __builtin_sub_overflow(a, b, &res);
65}
66
67#define RETURN_IF(TYPE, BUILTIN) \
68 if constexpr (cpp::is_same_v<T, TYPE>) \
69 return BUILTIN(a, b, carry_in, carry_out);
70
71// Returns the result of 'a + b' taking into account 'carry_in'.
72// The carry out is stored in 'carry_out' it not 'nullptr', dropped otherwise.
73// We keep the pass by pointer interface for consistency with the intrinsic.
74template <typename T>
75[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
76add_with_carry(T a, T b, T carry_in, T &carry_out) {
77 if constexpr (!cpp::is_constant_evaluated()) {
78#if __has_builtin(__builtin_addcb)
79 RETURN_IF(unsigned char, __builtin_addcb)
80#elif __has_builtin(__builtin_addcs)
81 RETURN_IF(unsigned short, __builtin_addcs)
82#elif __has_builtin(__builtin_addc)
83 RETURN_IF(unsigned int, __builtin_addc)
84#elif __has_builtin(__builtin_addcl)
85 RETURN_IF(unsigned long, __builtin_addcl)
86#elif __has_builtin(__builtin_addcll)
87 RETURN_IF(unsigned long long, __builtin_addcll)
88#endif
89 }
90 T sum = {};
91 T carry1 = add_overflow(a, b, sum);
92 T carry2 = add_overflow(sum, carry_in, sum);
93 carry_out = carry1 | carry2;
94 return sum;
95}
96
97// Returns the result of 'a - b' taking into account 'carry_in'.
98// The carry out is stored in 'carry_out' it not 'nullptr', dropped otherwise.
99// We keep the pass by pointer interface for consistency with the intrinsic.
100template <typename T>
101[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
102sub_with_borrow(T a, T b, T carry_in, T &carry_out) {
103 if constexpr (!cpp::is_constant_evaluated()) {
104#if __has_builtin(__builtin_subcb)
105 RETURN_IF(unsigned char, __builtin_subcb)
106#elif __has_builtin(__builtin_subcs)
107 RETURN_IF(unsigned short, __builtin_subcs)
108#elif __has_builtin(__builtin_subc)
109 RETURN_IF(unsigned int, __builtin_subc)
110#elif __has_builtin(__builtin_subcl)
111 RETURN_IF(unsigned long, __builtin_subcl)
112#elif __has_builtin(__builtin_subcll)
113 RETURN_IF(unsigned long long, __builtin_subcll)
114#endif
115 }
116 T sub = {};
117 T carry1 = sub_overflow(a, b, sub);
118 T carry2 = sub_overflow(sub, carry_in, sub);
119 carry_out = carry1 | carry2;
120 return sub;
121}
122
123#undef RETURN_IF
124
125template <typename T>
126[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
127first_leading_zero(T value) {
128 return value == cpp::numeric_limits<T>::max() ? 0
129 : cpp::countl_one(value) + 1;
130}
131
132template <typename T>
133[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
134first_leading_one(T value) {
135 return first_leading_zero(static_cast<T>(~value));
136}
137
138template <typename T>
139[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
140first_trailing_zero(T value) {
141 return value == cpp::numeric_limits<T>::max()
142 ? 0
143 : cpp::countr_zero(static_cast<T>(~value)) + 1;
144}
145
146template <typename T>
147[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
148first_trailing_one(T value) {
149 return value == 0 ? 0 : cpp::countr_zero(value) + 1;
150}
151
152template <typename T>
153[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
154count_zeros(T value) {
155 return cpp::popcount<T>(static_cast<T>(~value));
156}
157
158} // namespace LIBC_NAMESPACE_DECL
159
160#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXTRAS_H