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
18 namespace LIBC_NAMESPACE {
19
20 // Create a bitmask with the count right-most bits set to 1, and all other bits
21 // set to 0. Only unsigned types are allowed.
22 template <typename T, size_t count>
23 LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
mask_trailing_ones()24 mask_trailing_ones() {
25 constexpr unsigned T_BITS = CHAR_BIT * sizeof(T);
26 static_assert(count <= T_BITS && "Invalid bit index");
27 return count == 0 ? 0 : (T(-1) >> (T_BITS - count));
28 }
29
30 // Create a bitmask with the count left-most bits set to 1, and all other bits
31 // set to 0. Only unsigned types are allowed.
32 template <typename T, size_t count>
33 LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
mask_leading_ones()34 mask_leading_ones() {
35 return T(~mask_trailing_ones<T, CHAR_BIT * sizeof(T) - count>());
36 }
37
38 // Create a bitmask with the count right-most bits set to 0, and all other bits
39 // set to 1. Only unsigned types are allowed.
40 template <typename T, size_t count>
41 LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
mask_trailing_zeros()42 mask_trailing_zeros() {
43 return mask_leading_ones<T, CHAR_BIT * sizeof(T) - count>();
44 }
45
46 // Create a bitmask with the count left-most bits set to 0, and all other bits
47 // set to 1. Only unsigned types are allowed.
48 template <typename T, size_t count>
49 LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
mask_leading_zeros()50 mask_leading_zeros() {
51 return mask_trailing_ones<T, CHAR_BIT * sizeof(T) - count>();
52 }
53
54 // Returns whether 'a + b' overflows, the result is stored in 'res'.
55 template <typename T>
add_overflow(T a,T b,T & res)56 [[nodiscard]] LIBC_INLINE constexpr bool add_overflow(T a, T b, T &res) {
57 return __builtin_add_overflow(a, b, &res);
58 }
59
60 // Returns whether 'a - b' overflows, the result is stored in 'res'.
61 template <typename T>
sub_overflow(T a,T b,T & res)62 [[nodiscard]] LIBC_INLINE constexpr bool sub_overflow(T a, T b, T &res) {
63 return __builtin_sub_overflow(a, b, &res);
64 }
65
66 #define RETURN_IF(TYPE, BUILTIN) \
67 if constexpr (cpp::is_same_v<T, TYPE>) \
68 return BUILTIN(a, b, carry_in, carry_out);
69
70 // Returns the result of 'a + b' taking into account 'carry_in'.
71 // The carry out is stored in 'carry_out' it not 'nullptr', dropped otherwise.
72 // We keep the pass by pointer interface for consistency with the intrinsic.
73 template <typename T>
74 [[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)75 add_with_carry(T a, T b, T carry_in, T &carry_out) {
76 if constexpr (!cpp::is_constant_evaluated()) {
77 #if __has_builtin(__builtin_addcb)
78 RETURN_IF(unsigned char, __builtin_addcb)
79 #elif __has_builtin(__builtin_addcs)
80 RETURN_IF(unsigned short, __builtin_addcs)
81 #elif __has_builtin(__builtin_addc)
82 RETURN_IF(unsigned int, __builtin_addc)
83 #elif __has_builtin(__builtin_addcl)
84 RETURN_IF(unsigned long, __builtin_addcl)
85 #elif __has_builtin(__builtin_addcll)
86 RETURN_IF(unsigned long long, __builtin_addcll)
87 #endif
88 }
89 T sum = {};
90 T carry1 = add_overflow(a, b, sum);
91 T carry2 = add_overflow(sum, carry_in, sum);
92 carry_out = carry1 | carry2;
93 return sum;
94 }
95
96 // Returns the result of 'a - b' taking into account 'carry_in'.
97 // The carry out is stored in 'carry_out' it not 'nullptr', dropped otherwise.
98 // We keep the pass by pointer interface for consistency with the intrinsic.
99 template <typename T>
100 [[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)101 sub_with_borrow(T a, T b, T carry_in, T &carry_out) {
102 if constexpr (!cpp::is_constant_evaluated()) {
103 #if __has_builtin(__builtin_subcb)
104 RETURN_IF(unsigned char, __builtin_subcb)
105 #elif __has_builtin(__builtin_subcs)
106 RETURN_IF(unsigned short, __builtin_subcs)
107 #elif __has_builtin(__builtin_subc)
108 RETURN_IF(unsigned int, __builtin_subc)
109 #elif __has_builtin(__builtin_subcl)
110 RETURN_IF(unsigned long, __builtin_subcl)
111 #elif __has_builtin(__builtin_subcll)
112 RETURN_IF(unsigned long long, __builtin_subcll)
113 #endif
114 }
115 T sub = {};
116 T carry1 = sub_overflow(a, b, sub);
117 T carry2 = sub_overflow(sub, carry_in, sub);
118 carry_out = carry1 | carry2;
119 return sub;
120 }
121
122 #undef RETURN_IF
123
124 template <typename T>
125 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
first_leading_zero(T value)126 first_leading_zero(T value) {
127 return value == cpp::numeric_limits<T>::max() ? 0
128 : cpp::countl_one(value) + 1;
129 }
130
131 template <typename T>
132 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
first_leading_one(T value)133 first_leading_one(T value) {
134 return first_leading_zero(static_cast<T>(~value));
135 }
136
137 template <typename T>
138 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
first_trailing_zero(T value)139 first_trailing_zero(T value) {
140 return value == cpp::numeric_limits<T>::max()
141 ? 0
142 : cpp::countr_zero(static_cast<T>(~value)) + 1;
143 }
144
145 template <typename T>
146 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
first_trailing_one(T value)147 first_trailing_one(T value) {
148 return value == cpp::numeric_limits<T>::max() ? 0
149 : cpp::countr_zero(value) + 1;
150 }
151
152 template <typename T>
153 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
count_zeros(T value)154 count_zeros(T value) {
155 return cpp::popcount<T>(static_cast<T>(~value));
156 }
157
158 } // namespace LIBC_NAMESPACE
159
160 #endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXTRAS_H
161