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// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef LIB_STDCOMPAT_INCLUDE_LIB_STDCOMPAT_BIT_H_
#define LIB_STDCOMPAT_INCLUDE_LIB_STDCOMPAT_BIT_H_
#include <cstring>
#include <limits>
#include "internal/bit.h"
#include "memory.h"
#include "version.h"
#if __has_include(<bit>) && !defined(LIB_STDCOMPAT_USE_POLYFILLS)
#include <bit>
#endif //__has_include(<bit>) && !defined(LIB_STDCOMPAT_USE_POLYFILLS)
namespace cpp20 {
#if defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L && \
!defined(LIB_STDCOMPAT_USE_POLYFILLS)
using std::bit_cast;
#else // Use builtin to provide constexpr bit_cast.
#if defined(__has_builtin) && !defined(LIB_STDCOMPAT_NO_BUILTIN_BITCAST)
#if __has_builtin(__builtin_bit_cast)
template <typename To, typename From>
constexpr std::enable_if_t<sizeof(To) == sizeof(From) && std::is_trivially_copyable<To>::value &&
std::is_trivially_copyable<From>::value,
To>
bit_cast(const From& from) {
return __builtin_bit_cast(To, from);
}
// Since there are two #if checks, using #else would require code duplication.
// Define a temporary internal macro to indicate that bit_cast was defined.
#define LIB_STDCOMPAT_BIT_CAST_DEFINED_
#endif // __has_builtin(__builtin_bit_cast)
#endif // defined(__has_builtin) && !defined(LIB_STDCOMPAT_NO_BUILTIN_BITCAST)
// Use memcpy instead, not constexpr though.
#ifndef LIB_STDCOMPAT_BIT_CAST_DEFINED_
#define LIB_STDCOMPAT_NONCONSTEXPR_BITCAST 1
template <typename To, typename From>
std::enable_if_t<sizeof(To) == sizeof(From) && std::is_trivially_copyable<To>::value &&
std::is_trivially_copyable<From>::value,
To>
bit_cast(const From& from) {
std::aligned_storage_t<sizeof(To)> uninitialized_to;
std::memcpy(static_cast<void*>(&uninitialized_to),
static_cast<const void*>(cpp17::addressof(from)), sizeof(To));
return *reinterpret_cast<const To*>(&uninitialized_to);
}
#endif // LIB_STDCOMPAT_BIT_CAST_DEFINED_
#undef LIB_STDCOMPAT_BIT_CAST_DEFINED_
#endif // __cpp_lib_bit_cast >= 201806L && !defined(LIB_STDCOMPAT_USE_POLYFILLS)
#if defined(__cpp_lib_bitops) && __cpp_lib_bitops >= 201907L && \
!defined(LIB_STDCOMPAT_USE_POLYFILLS)
using std::countl_one;
using std::countl_zero;
using std::countr_one;
using std::countr_zero;
using std::popcount;
using std::rotl;
using std::rotr;
#else
template <class T>
constexpr std::enable_if_t<std::is_unsigned<T>::value, int> countr_zero(T x) noexcept {
if (x == 0) {
return std::numeric_limits<T>::digits;
}
return internal::count_zeros_from_right(x);
}
template <class T>
constexpr std::enable_if_t<std::is_unsigned<T>::value, int> countl_zero(T x) noexcept {
if (x == 0) {
return std::numeric_limits<T>::digits;
}
return internal::count_zeros_from_left(x);
}
template <class T>
constexpr std::enable_if_t<std::is_unsigned<T>::value, int> countl_one(T x) noexcept {
return countl_zero(static_cast<T>(~x));
}
template <class T>
constexpr std::enable_if_t<std::is_unsigned<T>::value, int> countr_one(T x) noexcept {
return countr_zero(static_cast<T>(~x));
}
template <class T>
[[gnu::warn_unused_result]] constexpr std::enable_if_t<std::is_unsigned<T>::value, T> rotl(
T x, int s) noexcept {
return internal::rotl(x, s);
}
template <class T>
[[gnu::warn_unused_result]] constexpr std::enable_if_t<std::is_unsigned<T>::value, T> rotr(
T x, int s) noexcept {
return internal::rotr(x, s);
}
template <class T>
constexpr int popcount(T x) noexcept {
return internal::popcount(x);
}
#endif
#if defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L && \
!defined(LIB_STDCOMPAT_USE_POLYFILLS)
using std::bit_ceil;
using std::bit_floor;
using std::bit_width;
using std::has_single_bit;
#else // Provide polyfills for power of two bit functions.
template <typename T>
constexpr std::enable_if_t<std::is_unsigned<T>::value, bool> has_single_bit(T value) {
return popcount(value) == static_cast<T>(1);
}
template <typename T>
constexpr std::enable_if_t<std::is_unsigned<T>::value, T> bit_width(T value) {
return internal::bit_width(value);
}
template <typename T>
constexpr std::enable_if_t<std::is_unsigned<T>::value, T> bit_ceil(T value) {
if (value <= 1) {
return T(1);
}
return internal::bit_ceil<T>(value);
}
template <typename T>
constexpr std::enable_if_t<std::is_unsigned<T>::value, T> bit_floor(T value) {
if (value == 0) {
return 0;
}
return internal::bit_floor(value);
}
#endif // __cpp_lib_int_pow2 >= 202002L && !defined(LIB_STDCOMPAT_USE_POLYFILLS)
#if defined(__cpp_lib_endian) && __cpp_lib_endian >= 201907L && \
!defined(LIB_STDCOMPAT_USE_POLYFILLS)
using std::endian;
#else // Provide polyfill for endian enum.
enum class endian {
little = 0x11771E,
big = 0xB16,
native = internal::native_endianess<little, big>(),
};
#endif
} // namespace cpp20
#endif // LIB_STDCOMPAT_INCLUDE_LIB_STDCOMPAT_BIT_H_
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