//===-- llvm/ADT/bit.h - C++20 <bit> ----------------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file implements the C++20 <bit> header.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_BIT_H
#define LLVM_ADT_BIT_H
#include "llvm/Support/Compiler.h"
#include <cstdint>
#include <limits>
#include <type_traits>
#if !__has_builtin(__builtin_bit_cast)
#include <cstring>
#endif
#if defined(_MSC_VER) && !defined(_DEBUG)
#include <cstdlib> // for _byteswap_{ushort,ulong,uint64}
#endif
#ifdef _MSC_VER
// Declare these intrinsics manually rather including intrin.h. It's very
// expensive, and bit.h is popular via MathExtras.h.
// #include <intrin.h>
extern "C" {
unsigned char _BitScanForward(unsigned long *_Index, unsigned long _Mask);
unsigned char _BitScanForward64(unsigned long *_Index, unsigned __int64 _Mask);
unsigned char _BitScanReverse(unsigned long *_Index, unsigned long _Mask);
unsigned char _BitScanReverse64(unsigned long *_Index, unsigned __int64 _Mask);
}
#endif
namespace llvm {
// This implementation of bit_cast is different from the C++20 one in two ways:
// - It isn't constexpr because that requires compiler support.
// - It requires trivially-constructible To, to avoid UB in the implementation.
template <
typename To, typename From,
typename = std::enable_if_t<sizeof(To) == sizeof(From)>,
typename = std::enable_if_t<std::is_trivially_constructible<To>::value>,
typename = std::enable_if_t<std::is_trivially_copyable<To>::value>,
typename = std::enable_if_t<std::is_trivially_copyable<From>::value>>
[[nodiscard]] inline To bit_cast(const From &from) noexcept {
#if __has_builtin(__builtin_bit_cast)
return __builtin_bit_cast(To, from);
#else
To to;
std::memcpy(&to, &from, sizeof(To));
return to;
#endif
}
/// Reverses the bytes in the given integer value V.
template <typename T, typename = std::enable_if_t<std::is_integral_v<T>>>
[[nodiscard]] constexpr T byteswap(T V) noexcept {
if constexpr (sizeof(T) == 1) {
return V;
} else if constexpr (sizeof(T) == 2) {
uint16_t UV = V;
#if defined(_MSC_VER) && !defined(_DEBUG)
// The DLL version of the runtime lacks these functions (bug!?), but in a
// release build they're replaced with BSWAP instructions anyway.
return _byteswap_ushort(UV);
#else
uint16_t Hi = UV << 8;
uint16_t Lo = UV >> 8;
return Hi | Lo;
#endif
} else if constexpr (sizeof(T) == 4) {
uint32_t UV = V;
#if __has_builtin(__builtin_bswap32)
return __builtin_bswap32(UV);
#elif defined(_MSC_VER) && !defined(_DEBUG)
return _byteswap_ulong(UV);
#else
uint32_t Byte0 = UV & 0x000000FF;
uint32_t Byte1 = UV & 0x0000FF00;
uint32_t Byte2 = UV & 0x00FF0000;
uint32_t Byte3 = UV & 0xFF000000;
return (Byte0 << 24) | (Byte1 << 8) | (Byte2 >> 8) | (Byte3 >> 24);
#endif
} else if constexpr (sizeof(T) == 8) {
uint64_t UV = V;
#if __has_builtin(__builtin_bswap64)
return __builtin_bswap64(UV);
#elif defined(_MSC_VER) && !defined(_DEBUG)
return _byteswap_uint64(UV);
#else
uint64_t Hi = llvm::byteswap<uint32_t>(UV);
uint32_t Lo = llvm::byteswap<uint32_t>(UV >> 32);
return (Hi << 32) | Lo;
#endif
} else {
static_assert(!sizeof(T *), "Don't know how to handle the given type.");
return 0;
}
}
template <typename T, typename = std::enable_if_t<std::is_unsigned_v<T>>>
[[nodiscard]] constexpr inline bool has_single_bit(T Value) noexcept {
return (Value != 0) && ((Value & (Value - 1)) == 0);
}
namespace detail {
template <typename T, std::size_t SizeOfT> struct TrailingZerosCounter {
static unsigned count(T Val) {
if (!Val)
return std::numeric_limits<T>::digits;
if (Val & 0x1)
return 0;
// Bisection method.
unsigned ZeroBits = 0;
T Shift = std::numeric_limits<T>::digits >> 1;
T Mask = std::numeric_limits<T>::max() >> Shift;
while (Shift) {
if ((Val & Mask) == 0) {
Val >>= Shift;
ZeroBits |= Shift;
}
Shift >>= 1;
Mask >>= Shift;
}
return ZeroBits;
}
};
#if defined(__GNUC__) || defined(_MSC_VER)
template <typename T> struct TrailingZerosCounter<T, 4> {
static unsigned count(T Val) {
if (Val == 0)
return 32;
#if __has_builtin(__builtin_ctz) || defined(__GNUC__)
return __builtin_ctz(Val);
#elif defined(_MSC_VER)
unsigned long Index;
_BitScanForward(&Index, Val);
return Index;
#endif
}
};
#if !defined(_MSC_VER) || defined(_M_X64)
template <typename T> struct TrailingZerosCounter<T, 8> {
static unsigned count(T Val) {
if (Val == 0)
return 64;
#if __has_builtin(__builtin_ctzll) || defined(__GNUC__)
return __builtin_ctzll(Val);
#elif defined(_MSC_VER)
unsigned long Index;
_BitScanForward64(&Index, Val);
return Index;
#endif
}
};
#endif
#endif
} // namespace detail
/// Count number of 0's from the least significant bit to the most
/// stopping at the first 1.
///
/// Only unsigned integral types are allowed.
///
/// Returns std::numeric_limits<T>::digits on an input of 0.
template <typename T> [[nodiscard]] int countr_zero(T Val) {
static_assert(std::is_unsigned_v<T>,
"Only unsigned integral types are allowed.");
return llvm::detail::TrailingZerosCounter<T, sizeof(T)>::count(Val);
}
namespace detail {
template <typename T, std::size_t SizeOfT> struct LeadingZerosCounter {
static unsigned count(T Val) {
if (!Val)
return std::numeric_limits<T>::digits;
// Bisection method.
unsigned ZeroBits = 0;
for (T Shift = std::numeric_limits<T>::digits >> 1; Shift; Shift >>= 1) {
T Tmp = Val >> Shift;
if (Tmp)
Val = Tmp;
else
ZeroBits |= Shift;
}
return ZeroBits;
}
};
#if defined(__GNUC__) || defined(_MSC_VER)
template <typename T> struct LeadingZerosCounter<T, 4> {
static unsigned count(T Val) {
if (Val == 0)
return 32;
#if __has_builtin(__builtin_clz) || defined(__GNUC__)
return __builtin_clz(Val);
#elif defined(_MSC_VER)
unsigned long Index;
_BitScanReverse(&Index, Val);
return Index ^ 31;
#endif
}
};
#if !defined(_MSC_VER) || defined(_M_X64)
template <typename T> struct LeadingZerosCounter<T, 8> {
static unsigned count(T Val) {
if (Val == 0)
return 64;
#if __has_builtin(__builtin_clzll) || defined(__GNUC__)
return __builtin_clzll(Val);
#elif defined(_MSC_VER)
unsigned long Index;
_BitScanReverse64(&Index, Val);
return Index ^ 63;
#endif
}
};
#endif
#endif
} // namespace detail
/// Count number of 0's from the most significant bit to the least
/// stopping at the first 1.
///
/// Only unsigned integral types are allowed.
///
/// Returns std::numeric_limits<T>::digits on an input of 0.
template <typename T> [[nodiscard]] int countl_zero(T Val) {
static_assert(std::is_unsigned_v<T>,
"Only unsigned integral types are allowed.");
return llvm::detail::LeadingZerosCounter<T, sizeof(T)>::count(Val);
}
/// Count the number of ones from the most significant bit to the first
/// zero bit.
///
/// Ex. countl_one(0xFF0FFF00) == 8.
/// Only unsigned integral types are allowed.
///
/// Returns std::numeric_limits<T>::digits on an input of all ones.
template <typename T> [[nodiscard]] int countl_one(T Value) {
static_assert(std::is_unsigned_v<T>,
"Only unsigned integral types are allowed.");
return llvm::countl_zero<T>(~Value);
}
/// Count the number of ones from the least significant bit to the first
/// zero bit.
///
/// Ex. countr_one(0x00FF00FF) == 8.
/// Only unsigned integral types are allowed.
///
/// Returns std::numeric_limits<T>::digits on an input of all ones.
template <typename T> [[nodiscard]] int countr_one(T Value) {
static_assert(std::is_unsigned_v<T>,
"Only unsigned integral types are allowed.");
return llvm::countr_zero<T>(~Value);
}
/// Returns the number of bits needed to represent Value if Value is nonzero.
/// Returns 0 otherwise.
///
/// Ex. bit_width(5) == 3.
template <typename T> [[nodiscard]] int bit_width(T Value) {
static_assert(std::is_unsigned_v<T>,
"Only unsigned integral types are allowed.");
return std::numeric_limits<T>::digits - llvm::countl_zero(Value);
}
/// Returns the largest integral power of two no greater than Value if Value is
/// nonzero. Returns 0 otherwise.
///
/// Ex. bit_floor(5) == 4.
template <typename T> [[nodiscard]] T bit_floor(T Value) {
static_assert(std::is_unsigned_v<T>,
"Only unsigned integral types are allowed.");
if (!Value)
return 0;
return T(1) << (llvm::bit_width(Value) - 1);
}
/// Returns the smallest integral power of two no smaller than Value if Value is
/// nonzero. Returns 0 otherwise.
///
/// Ex. bit_ceil(5) == 8.
///
/// The return value is undefined if the input is larger than the largest power
/// of two representable in T.
template <typename T> [[nodiscard]] T bit_ceil(T Value) {
static_assert(std::is_unsigned_v<T>,
"Only unsigned integral types are allowed.");
if (Value < 2)
return 1;
return T(1) << llvm::bit_width<T>(Value - 1u);
}
namespace detail {
template <typename T, std::size_t SizeOfT> struct PopulationCounter {
static int count(T Value) {
// Generic version, forward to 32 bits.
static_assert(SizeOfT <= 4, "Not implemented!");
#if defined(__GNUC__)
return (int)__builtin_popcount(Value);
#else
uint32_t v = Value;
v = v - ((v >> 1) & 0x55555555);
v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
return int(((v + (v >> 4) & 0xF0F0F0F) * 0x1010101) >> 24);
#endif
}
};
template <typename T> struct PopulationCounter<T, 8> {
static int count(T Value) {
#if defined(__GNUC__)
return (int)__builtin_popcountll(Value);
#else
uint64_t v = Value;
v = v - ((v >> 1) & 0x5555555555555555ULL);
v = (v & 0x3333333333333333ULL) + ((v >> 2) & 0x3333333333333333ULL);
v = (v + (v >> 4)) & 0x0F0F0F0F0F0F0F0FULL;
return int((uint64_t)(v * 0x0101010101010101ULL) >> 56);
#endif
}
};
} // namespace detail
/// Count the number of set bits in a value.
/// Ex. popcount(0xF000F000) = 8
/// Returns 0 if the word is zero.
template <typename T, typename = std::enable_if_t<std::is_unsigned_v<T>>>
[[nodiscard]] inline int popcount(T Value) noexcept {
return detail::PopulationCounter<T, sizeof(T)>::count(Value);
}
} // namespace llvm
#endif