156ab87500
See: * https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc/77319 * https://discourse.llvm.org/t/rfc-project-hand-in-hand-llvm-libc-libc-code-sharing/77701 We're dropping support for C++03 for Zig due to the first change; it would be insane to ship 1018 duplicate header files just for this outdated use case. As a result of the second change, I had to bring in a subset of the headers from llvm-libc since libc++ now depends on these. Hopefully we can continue to get away with not copying the entirety of llvm-libc.
162 lines
6.0 KiB
C++
Vendored
162 lines
6.0 KiB
C++
Vendored
//===-- Mimics llvm/Support/MathExtras.h ------------------------*- C++ -*-===//
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// Provides useful math functions.
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_LIBC_SRC___SUPPORT_MATH_EXTRAS_H
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#define LLVM_LIBC_SRC___SUPPORT_MATH_EXTRAS_H
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#include "src/__support/CPP/bit.h" // countl_one, countr_zero
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#include "src/__support/CPP/limits.h" // CHAR_BIT, numeric_limits
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#include "src/__support/CPP/type_traits.h" // is_unsigned_v, is_constant_evaluated
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#include "src/__support/macros/attributes.h" // LIBC_INLINE
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#include "src/__support/macros/config.h"
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namespace LIBC_NAMESPACE_DECL {
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// Create a bitmask with the count right-most bits set to 1, and all other bits
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// set to 0. Only unsigned types are allowed.
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template <typename T, size_t count>
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LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
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mask_trailing_ones() {
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constexpr unsigned T_BITS = CHAR_BIT * sizeof(T);
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static_assert(count <= T_BITS && "Invalid bit index");
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return count == 0 ? 0 : (T(-1) >> (T_BITS - count));
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}
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// Create a bitmask with the count left-most bits set to 1, and all other bits
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// set to 0. Only unsigned types are allowed.
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template <typename T, size_t count>
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LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
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mask_leading_ones() {
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return T(~mask_trailing_ones<T, CHAR_BIT * sizeof(T) - count>());
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}
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// Create a bitmask with the count right-most bits set to 0, and all other bits
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// set to 1. Only unsigned types are allowed.
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template <typename T, size_t count>
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LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
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mask_trailing_zeros() {
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return mask_leading_ones<T, CHAR_BIT * sizeof(T) - count>();
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}
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// Create a bitmask with the count left-most bits set to 0, and all other bits
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// set to 1. Only unsigned types are allowed.
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template <typename T, size_t count>
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LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
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mask_leading_zeros() {
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return mask_trailing_ones<T, CHAR_BIT * sizeof(T) - count>();
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}
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// Returns whether 'a + b' overflows, the result is stored in 'res'.
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template <typename T>
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[[nodiscard]] LIBC_INLINE constexpr bool add_overflow(T a, T b, T &res) {
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return __builtin_add_overflow(a, b, &res);
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}
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// Returns whether 'a - b' overflows, the result is stored in 'res'.
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template <typename T>
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[[nodiscard]] LIBC_INLINE constexpr bool sub_overflow(T a, T b, T &res) {
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return __builtin_sub_overflow(a, b, &res);
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}
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#define RETURN_IF(TYPE, BUILTIN) \
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if constexpr (cpp::is_same_v<T, TYPE>) \
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return BUILTIN(a, b, carry_in, carry_out);
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// Returns the result of 'a + b' taking into account 'carry_in'.
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// The carry out is stored in 'carry_out' it not 'nullptr', dropped otherwise.
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// We keep the pass by pointer interface for consistency with the intrinsic.
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template <typename T>
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[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
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add_with_carry(T a, T b, T carry_in, T &carry_out) {
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if constexpr (!cpp::is_constant_evaluated()) {
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#if __has_builtin(__builtin_addcb)
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RETURN_IF(unsigned char, __builtin_addcb)
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#elif __has_builtin(__builtin_addcs)
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RETURN_IF(unsigned short, __builtin_addcs)
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#elif __has_builtin(__builtin_addc)
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RETURN_IF(unsigned int, __builtin_addc)
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#elif __has_builtin(__builtin_addcl)
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RETURN_IF(unsigned long, __builtin_addcl)
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#elif __has_builtin(__builtin_addcll)
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RETURN_IF(unsigned long long, __builtin_addcll)
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#endif
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}
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T sum = {};
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T carry1 = add_overflow(a, b, sum);
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T carry2 = add_overflow(sum, carry_in, sum);
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carry_out = carry1 | carry2;
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return sum;
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}
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// Returns the result of 'a - b' taking into account 'carry_in'.
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// The carry out is stored in 'carry_out' it not 'nullptr', dropped otherwise.
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// We keep the pass by pointer interface for consistency with the intrinsic.
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template <typename T>
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[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
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sub_with_borrow(T a, T b, T carry_in, T &carry_out) {
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if constexpr (!cpp::is_constant_evaluated()) {
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#if __has_builtin(__builtin_subcb)
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RETURN_IF(unsigned char, __builtin_subcb)
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#elif __has_builtin(__builtin_subcs)
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RETURN_IF(unsigned short, __builtin_subcs)
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#elif __has_builtin(__builtin_subc)
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RETURN_IF(unsigned int, __builtin_subc)
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#elif __has_builtin(__builtin_subcl)
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RETURN_IF(unsigned long, __builtin_subcl)
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#elif __has_builtin(__builtin_subcll)
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RETURN_IF(unsigned long long, __builtin_subcll)
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#endif
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}
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T sub = {};
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T carry1 = sub_overflow(a, b, sub);
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T carry2 = sub_overflow(sub, carry_in, sub);
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carry_out = carry1 | carry2;
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return sub;
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}
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#undef RETURN_IF
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template <typename T>
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[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
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first_leading_zero(T value) {
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return value == cpp::numeric_limits<T>::max() ? 0
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: cpp::countl_one(value) + 1;
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}
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template <typename T>
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[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
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first_leading_one(T value) {
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return first_leading_zero(static_cast<T>(~value));
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}
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template <typename T>
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[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
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first_trailing_zero(T value) {
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return value == cpp::numeric_limits<T>::max()
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? 0
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: cpp::countr_zero(static_cast<T>(~value)) + 1;
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}
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template <typename T>
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[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
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first_trailing_one(T value) {
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return value == cpp::numeric_limits<T>::max() ? 0
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: cpp::countr_zero(value) + 1;
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}
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template <typename T>
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[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
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count_zeros(T value) {
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return cpp::popcount<T>(static_cast<T>(~value));
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}
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} // namespace LIBC_NAMESPACE_DECL
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#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXTRAS_H
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