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
19 namespace 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.
23 template <typename T, size_t count>
24 LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
mask_trailing_ones()25 mask_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.
33 template <typename T, size_t count>
34 LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
mask_leading_ones()35 mask_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.
41 template <typename T, size_t count>
42 LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
mask_trailing_zeros()43 mask_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.
49 template <typename T, size_t count>
50 LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
mask_leading_zeros()51 mask_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'.
56 template <typename T>
add_overflow(T a,T b,T & res)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'.
62 template <typename T>
sub_overflow(T a,T b,T & res)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.
74 template <typename T>
75 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
add_with_carry(T a,T b,T carry_in,T & carry_out)76 add_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.
100 template <typename T>
101 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
sub_with_borrow(T a,T b,T carry_in,T & carry_out)102 sub_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
125 template <typename T>
126 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
first_leading_zero(T value)127 first_leading_zero(T value) {
128 return value == cpp::numeric_limits<T>::max() ? 0
129 : cpp::countl_one(value) + 1;
130 }
131
132 template <typename T>
133 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
first_leading_one(T value)134 first_leading_one(T value) {
135 return first_leading_zero(static_cast<T>(~value));
136 }
137
138 template <typename T>
139 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
first_trailing_zero(T value)140 first_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
146 template <typename T>
147 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
first_trailing_one(T value)148 first_trailing_one(T value) {
149 return value == cpp::numeric_limits<T>::max() ? 0
150 : cpp::countr_zero(value) + 1;
151 }
152
153 template <typename T>
154 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
count_zeros(T value)155 count_zeros(T value) {
156 return cpp::popcount<T>(static_cast<T>(~value));
157 }
158
159 } // namespace LIBC_NAMESPACE_DECL
160
161 #endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXTRAS_H
162