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//===-- Mimics llvm/Support/MathExtras.h ------------------------*- C++ -*-===//
// Provides useful math functions.
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_LIBC_SRC___SUPPORT_MATH_EXTRAS_H
#define LLVM_LIBC_SRC___SUPPORT_MATH_EXTRAS_H
#include "src/__support/CPP/limits.h" // CHAR_BIT
#include "src/__support/CPP/type_traits.h" // is_unsigned_v
#include "src/__support/macros/attributes.h" // LIBC_INLINE
#include "src/__support/macros/config.h" // LIBC_HAS_BUILTIN
namespace LIBC_NAMESPACE {
// Create a bitmask with the count right-most bits set to 1, and all other bits
// set to 0. Only unsigned types are allowed.
template <typename T, size_t count>
LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
mask_trailing_ones() {
constexpr unsigned T_BITS = CHAR_BIT * sizeof(T);
static_assert(count <= T_BITS && "Invalid bit index");
return count == 0 ? 0 : (T(-1) >> (T_BITS - count));
}
// Create a bitmask with the count left-most bits set to 1, and all other bits
// set to 0. Only unsigned types are allowed.
template <typename T, size_t count>
LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
mask_leading_ones() {
constexpr T MASK(mask_trailing_ones<T, CHAR_BIT * sizeof(T) - count>());
return T(~MASK); // bitwise NOT performs integer promotion.
}
// Add with carry
template <typename T> struct SumCarry {
T sum;
T carry;
};
// This version is always valid for constexpr.
template <typename T>
LIBC_INLINE constexpr cpp::enable_if_t<
cpp::is_integral_v<T> && cpp::is_unsigned_v<T>, SumCarry<T>>
add_with_carry_const(T a, T b, T carry_in) {
T tmp = a + carry_in;
T sum = b + tmp;
T carry_out = (sum < b) + (tmp < a);
return {sum, carry_out};
}
template <typename T>
LIBC_INLINE constexpr cpp::enable_if_t<
cpp::is_integral_v<T> && cpp::is_unsigned_v<T>, SumCarry<T>>
add_with_carry(T a, T b, T carry_in) {
return add_with_carry_const<T>(a, b, carry_in);
}
#if LIBC_HAS_BUILTIN(__builtin_addc)
// https://clang.llvm.org/docs/LanguageExtensions.html#multiprecision-arithmetic-builtins
template <>
LIBC_INLINE constexpr SumCarry<unsigned char>
add_with_carry<unsigned char>(unsigned char a, unsigned char b,
unsigned char carry_in) {
if (__builtin_is_constant_evaluated()) {
return add_with_carry_const<unsigned char>(a, b, carry_in);
} else {
SumCarry<unsigned char> result{0, 0};
result.sum = __builtin_addcb(a, b, carry_in, &result.carry);
return result;
}
}
template <>
LIBC_INLINE constexpr SumCarry<unsigned short>
add_with_carry<unsigned short>(unsigned short a, unsigned short b,
unsigned short carry_in) {
if (__builtin_is_constant_evaluated()) {
return add_with_carry_const<unsigned short>(a, b, carry_in);
} else {
SumCarry<unsigned short> result{0, 0};
result.sum = __builtin_addcs(a, b, carry_in, &result.carry);
return result;
}
}
template <>
LIBC_INLINE constexpr SumCarry<unsigned int>
add_with_carry<unsigned int>(unsigned int a, unsigned int b,
unsigned int carry_in) {
if (__builtin_is_constant_evaluated()) {
return add_with_carry_const<unsigned int>(a, b, carry_in);
} else {
SumCarry<unsigned int> result{0, 0};
result.sum = __builtin_addc(a, b, carry_in, &result.carry);
return result;
}
}
template <>
LIBC_INLINE constexpr SumCarry<unsigned long>
add_with_carry<unsigned long>(unsigned long a, unsigned long b,
unsigned long carry_in) {
if (__builtin_is_constant_evaluated()) {
return add_with_carry_const<unsigned long>(a, b, carry_in);
} else {
SumCarry<unsigned long> result{0, 0};
result.sum = __builtin_addcl(a, b, carry_in, &result.carry);
return result;
}
}
template <>
LIBC_INLINE constexpr SumCarry<unsigned long long>
add_with_carry<unsigned long long>(unsigned long long a, unsigned long long b,
unsigned long long carry_in) {
if (__builtin_is_constant_evaluated()) {
return add_with_carry_const<unsigned long long>(a, b, carry_in);
} else {
SumCarry<unsigned long long> result{0, 0};
result.sum = __builtin_addcll(a, b, carry_in, &result.carry);
return result;
}
}
#endif // LIBC_HAS_BUILTIN(__builtin_addc)
// Subtract with borrow
template <typename T> struct DiffBorrow {
T diff;
T borrow;
};
// This version is always valid for constexpr.
template <typename T>
LIBC_INLINE constexpr cpp::enable_if_t<
cpp::is_integral_v<T> && cpp::is_unsigned_v<T>, DiffBorrow<T>>
sub_with_borrow_const(T a, T b, T borrow_in) {
T tmp = a - b;
T diff = tmp - borrow_in;
T borrow_out = (diff > tmp) + (tmp > a);
return {diff, borrow_out};
}
// This version is not always valid for constepxr because it's overriden below
// if builtins are available.
template <typename T>
LIBC_INLINE constexpr cpp::enable_if_t<
cpp::is_integral_v<T> && cpp::is_unsigned_v<T>, DiffBorrow<T>>
sub_with_borrow(T a, T b, T borrow_in) {
return sub_with_borrow_const<T>(a, b, borrow_in);
}
#if LIBC_HAS_BUILTIN(__builtin_subc)
// https://clang.llvm.org/docs/LanguageExtensions.html#multiprecision-arithmetic-builtins
template <>
LIBC_INLINE constexpr DiffBorrow<unsigned char>
sub_with_borrow<unsigned char>(unsigned char a, unsigned char b,
unsigned char borrow_in) {
if (__builtin_is_constant_evaluated()) {
return sub_with_borrow_const<unsigned char>(a, b, borrow_in);
} else {
DiffBorrow<unsigned char> result{0, 0};
result.diff = __builtin_subcb(a, b, borrow_in, &result.borrow);
return result;
}
}
template <>
LIBC_INLINE constexpr DiffBorrow<unsigned short>
sub_with_borrow<unsigned short>(unsigned short a, unsigned short b,
unsigned short borrow_in) {
if (__builtin_is_constant_evaluated()) {
return sub_with_borrow_const<unsigned short>(a, b, borrow_in);
} else {
DiffBorrow<unsigned short> result{0, 0};
result.diff = __builtin_subcs(a, b, borrow_in, &result.borrow);
return result;
}
}
template <>
LIBC_INLINE constexpr DiffBorrow<unsigned int>
sub_with_borrow<unsigned int>(unsigned int a, unsigned int b,
unsigned int borrow_in) {
if (__builtin_is_constant_evaluated()) {
return sub_with_borrow_const<unsigned int>(a, b, borrow_in);
} else {
DiffBorrow<unsigned int> result{0, 0};
result.diff = __builtin_subc(a, b, borrow_in, &result.borrow);
return result;
}
}
template <>
LIBC_INLINE constexpr DiffBorrow<unsigned long>
sub_with_borrow<unsigned long>(unsigned long a, unsigned long b,
unsigned long borrow_in) {
if (__builtin_is_constant_evaluated()) {
return sub_with_borrow_const<unsigned long>(a, b, borrow_in);
} else {
DiffBorrow<unsigned long> result{0, 0};
result.diff = __builtin_subcl(a, b, borrow_in, &result.borrow);
return result;
}
}
template <>
LIBC_INLINE constexpr DiffBorrow<unsigned long long>
sub_with_borrow<unsigned long long>(unsigned long long a, unsigned long long b,
unsigned long long borrow_in) {
if (__builtin_is_constant_evaluated()) {
return sub_with_borrow_const<unsigned long long>(a, b, borrow_in);
} else {
DiffBorrow<unsigned long long> result{0, 0};
result.diff = __builtin_subcll(a, b, borrow_in, &result.borrow);
return result;
}
}
#endif // LIBC_HAS_BUILTIN(__builtin_subc)
} // namespace LIBC_NAMESPACE
#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXTRAS_H
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