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abseil-cpp/absl/numeric/internal/bits.h

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// Copyright 2020 The Abseil Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef ABSL_NUMERIC_INTERNAL_BITS_H_
#define ABSL_NUMERIC_INTERNAL_BITS_H_
#include <cstdint>
#include <limits>
#include <type_traits>
// Clang on Windows has __builtin_clzll; otherwise we need to use the
// windows intrinsic functions.
#if defined(_MSC_VER) && !defined(__clang__)
#include <intrin.h>
#if defined(_M_X64)
#pragma intrinsic(_BitScanReverse64)
#pragma intrinsic(_BitScanForward64)
#endif
#pragma intrinsic(_BitScanReverse)
#pragma intrinsic(_BitScanForward)
#endif
#include "absl/base/attributes.h"
#include "absl/base/config.h"
#if ABSL_HAVE_BUILTIN(__builtin_popcountl) && \
ABSL_HAVE_BUILTIN(__builtin_popcountll)
#define ABSL_INTERNAL_CONSTEXPR_POPCOUNT constexpr
#define ABSL_INTERNAL_HAS_CONSTEXPR_POPCOUNT 1
#else
#define ABSL_INTERNAL_CONSTEXPR_POPCOUNT
#define ABSL_INTERNAL_HAS_CONSTEXPR_POPCOUNT 0
#endif
#if ABSL_HAVE_BUILTIN(__builtin_clz) && ABSL_HAVE_BUILTIN(__builtin_clzll)
#define ABSL_INTERNAL_CONSTEXPR_CLZ constexpr
#define ABSL_INTERNAL_HAS_CONSTEXPR_CLZ 1
#else
#define ABSL_INTERNAL_CONSTEXPR_CLZ
#define ABSL_INTERNAL_HAS_CONSTEXPR_CLZ 0
#endif
#if ABSL_HAVE_BUILTIN(__builtin_ctz) && ABSL_HAVE_BUILTIN(__builtin_ctzll)
#define ABSL_INTERNAL_CONSTEXPR_CTZ constexpr
#define ABSL_INTERNAL_HAS_CONSTEXPR_CTZ 1
#else
#define ABSL_INTERNAL_CONSTEXPR_CTZ
#define ABSL_INTERNAL_HAS_CONSTEXPR_CTZ 0
#endif
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace numeric_internal {
constexpr bool IsPowerOf2(unsigned int x) noexcept {
return x != 0 && (x & (x - 1)) == 0;
}
template <class T>
ABSL_MUST_USE_RESULT ABSL_ATTRIBUTE_ALWAYS_INLINE constexpr T RotateRight(
T x, int s) noexcept {
static_assert(std::is_unsigned<T>::value, "T must be unsigned");
static_assert(IsPowerOf2(std::numeric_limits<T>::digits),
"T must have a power-of-2 size");
return static_cast<T>(x >> (s & (std::numeric_limits<T>::digits - 1))) |
static_cast<T>(x << ((-s) & (std::numeric_limits<T>::digits - 1)));
}
template <class T>
ABSL_MUST_USE_RESULT ABSL_ATTRIBUTE_ALWAYS_INLINE constexpr T RotateLeft(
T x, int s) noexcept {
static_assert(std::is_unsigned<T>::value, "T must be unsigned");
static_assert(IsPowerOf2(std::numeric_limits<T>::digits),
"T must have a power-of-2 size");
return static_cast<T>(x << (s & (std::numeric_limits<T>::digits - 1))) |
static_cast<T>(x >> ((-s) & (std::numeric_limits<T>::digits - 1)));
}
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_POPCOUNT inline int
Popcount32(uint32_t x) noexcept {
#if ABSL_HAVE_BUILTIN(__builtin_popcount)
static_assert(sizeof(unsigned int) == sizeof(x),
"__builtin_popcount does not take 32-bit arg");
return __builtin_popcount(x);
#else
x -= ((x >> 1) & 0x55555555);
x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
return static_cast<int>((((x + (x >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24);
#endif
}
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_POPCOUNT inline int
Popcount64(uint64_t x) noexcept {
#if ABSL_HAVE_BUILTIN(__builtin_popcountll)
static_assert(sizeof(unsigned long long) == sizeof(x), // NOLINT(runtime/int)
"__builtin_popcount does not take 64-bit arg");
return __builtin_popcountll(x);
#else
x -= (x >> 1) & 0x5555555555555555ULL;
x = ((x >> 2) & 0x3333333333333333ULL) + (x & 0x3333333333333333ULL);
return static_cast<int>(
(((x + (x >> 4)) & 0xF0F0F0F0F0F0F0FULL) * 0x101010101010101ULL) >> 56);
#endif
}
template <class T>
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_POPCOUNT inline int
Popcount(T x) noexcept {
static_assert(std::is_unsigned<T>::value, "T must be unsigned");
static_assert(IsPowerOf2(std::numeric_limits<T>::digits),
"T must have a power-of-2 size");
static_assert(sizeof(x) <= sizeof(uint64_t), "T is too large");
return sizeof(x) <= sizeof(uint32_t) ? Popcount32(x) : Popcount64(x);
}
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CLZ inline int
CountLeadingZeroes32(uint32_t x) {
#if ABSL_HAVE_BUILTIN(__builtin_clz)
// Use __builtin_clz, which uses the following instructions:
// x86: bsr, lzcnt
// ARM64: clz
// PPC: cntlzd
static_assert(sizeof(unsigned int) == sizeof(x),
"__builtin_clz does not take 32-bit arg");
// Handle 0 as a special case because __builtin_clz(0) is undefined.
return x == 0 ? 32 : __builtin_clz(x);
#elif defined(_MSC_VER) && !defined(__clang__)
unsigned long result = 0; // NOLINT(runtime/int)
if (_BitScanReverse(&result, x)) {
return 31 - result;
}
return 32;
#else
int zeroes = 28;
if (x >> 16) {
zeroes -= 16;
x >>= 16;
}
if (x >> 8) {
zeroes -= 8;
x >>= 8;
}
if (x >> 4) {
zeroes -= 4;
x >>= 4;
}
return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0"[x] + zeroes;
#endif
}
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CLZ inline int
CountLeadingZeroes16(uint16_t x) {
#if ABSL_HAVE_BUILTIN(__builtin_clzs)
static_assert(sizeof(unsigned short) == sizeof(x), // NOLINT(runtime/int)
"__builtin_clzs does not take 16-bit arg");
return x == 0 ? 16 : __builtin_clzs(x);
#else
return CountLeadingZeroes32(x) - 16;
#endif
}
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CLZ inline int
CountLeadingZeroes64(uint64_t x) {
#if ABSL_HAVE_BUILTIN(__builtin_clzll)
// Use __builtin_clzll, which uses the following instructions:
// x86: bsr, lzcnt
// ARM64: clz
// PPC: cntlzd
static_assert(sizeof(unsigned long long) == sizeof(x), // NOLINT(runtime/int)
"__builtin_clzll does not take 64-bit arg");
// Handle 0 as a special case because __builtin_clzll(0) is undefined.
return x == 0 ? 64 : __builtin_clzll(x);
#elif defined(_MSC_VER) && !defined(__clang__) && defined(_M_X64)
// MSVC does not have __buitin_clzll. Use _BitScanReverse64.
unsigned long result = 0; // NOLINT(runtime/int)
if (_BitScanReverse64(&result, x)) {
return 63 - result;
}
return 64;
#elif defined(_MSC_VER) && !defined(__clang__)
// MSVC does not have __buitin_clzll. Compose two calls to _BitScanReverse
unsigned long result = 0; // NOLINT(runtime/int)
if ((x >> 32) &&
_BitScanReverse(&result, static_cast<unsigned long>(x >> 32))) {
return 31 - result;
}
if (_BitScanReverse(&result, static_cast<unsigned long>(x))) {
return 63 - result;
}
return 64;
#else
int zeroes = 60;
if (x >> 32) {
zeroes -= 32;
x >>= 32;
}
if (x >> 16) {
zeroes -= 16;
x >>= 16;
}
if (x >> 8) {
zeroes -= 8;
x >>= 8;
}
if (x >> 4) {
zeroes -= 4;
x >>= 4;
}
return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0"[x] + zeroes;
#endif
}
template <typename T>
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CLZ inline int
CountLeadingZeroes(T x) {
static_assert(std::is_unsigned<T>::value, "T must be unsigned");
static_assert(IsPowerOf2(std::numeric_limits<T>::digits),
"T must have a power-of-2 size");
static_assert(sizeof(T) <= sizeof(uint64_t), "T too large");
return sizeof(T) <= sizeof(uint16_t)
? CountLeadingZeroes16(static_cast<uint16_t>(x)) -
(std::numeric_limits<uint16_t>::digits -
std::numeric_limits<T>::digits)
: (sizeof(T) <= sizeof(uint32_t)
? CountLeadingZeroes32(static_cast<uint32_t>(x)) -
(std::numeric_limits<uint32_t>::digits -
std::numeric_limits<T>::digits)
: CountLeadingZeroes64(x));
}
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CTZ inline int
CountTrailingZeroesNonzero32(uint32_t x) {
#if ABSL_HAVE_BUILTIN(__builtin_ctz)
static_assert(sizeof(unsigned int) == sizeof(x),
"__builtin_ctz does not take 32-bit arg");
return __builtin_ctz(x);
#elif defined(_MSC_VER) && !defined(__clang__)
unsigned long result = 0; // NOLINT(runtime/int)
_BitScanForward(&result, x);
return result;
#else
int c = 31;
x &= ~x + 1;
if (x & 0x0000FFFF) c -= 16;
if (x & 0x00FF00FF) c -= 8;
if (x & 0x0F0F0F0F) c -= 4;
if (x & 0x33333333) c -= 2;
if (x & 0x55555555) c -= 1;
return c;
#endif
}
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CTZ inline int
CountTrailingZeroesNonzero64(uint64_t x) {
#if ABSL_HAVE_BUILTIN(__builtin_ctzll)
static_assert(sizeof(unsigned long long) == sizeof(x), // NOLINT(runtime/int)
"__builtin_ctzll does not take 64-bit arg");
return __builtin_ctzll(x);
#elif defined(_MSC_VER) && !defined(__clang__) && defined(_M_X64)
unsigned long result = 0; // NOLINT(runtime/int)
_BitScanForward64(&result, x);
return result;
#elif defined(_MSC_VER) && !defined(__clang__)
unsigned long result = 0; // NOLINT(runtime/int)
if (static_cast<uint32_t>(x) == 0) {
_BitScanForward(&result, static_cast<unsigned long>(x >> 32));
return result + 32;
}
_BitScanForward(&result, static_cast<unsigned long>(x));
return result;
#else
int c = 63;
x &= ~x + 1;
if (x & 0x00000000FFFFFFFF) c -= 32;
if (x & 0x0000FFFF0000FFFF) c -= 16;
if (x & 0x00FF00FF00FF00FF) c -= 8;
if (x & 0x0F0F0F0F0F0F0F0F) c -= 4;
if (x & 0x3333333333333333) c -= 2;
if (x & 0x5555555555555555) c -= 1;
return c;
#endif
}
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CTZ inline int
CountTrailingZeroesNonzero16(uint16_t x) {
#if ABSL_HAVE_BUILTIN(__builtin_ctzs)
static_assert(sizeof(unsigned short) == sizeof(x), // NOLINT(runtime/int)
"__builtin_ctzs does not take 16-bit arg");
return __builtin_ctzs(x);
#else
return CountTrailingZeroesNonzero32(x);
#endif
}
template <class T>
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CTZ inline int
CountTrailingZeroes(T x) noexcept {
static_assert(std::is_unsigned<T>::value, "T must be unsigned");
static_assert(IsPowerOf2(std::numeric_limits<T>::digits),
"T must have a power-of-2 size");
static_assert(sizeof(T) <= sizeof(uint64_t), "T too large");
return x == 0 ? std::numeric_limits<T>::digits
: (sizeof(T) <= sizeof(uint16_t)
? CountTrailingZeroesNonzero16(static_cast<uint16_t>(x))
: (sizeof(T) <= sizeof(uint32_t)
? CountTrailingZeroesNonzero32(
static_cast<uint32_t>(x))
: CountTrailingZeroesNonzero64(x)));
}
// If T is narrower than unsigned, T{1} << bit_width will be promoted. We
// want to force it to wraparound so that bit_ceil of an invalid value are not
// core constant expressions.
template <class T>
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CLZ inline
typename std::enable_if<std::is_unsigned<T>::value, T>::type
BitCeilPromotionHelper(T x, T promotion) {
return (T{1} << (x + promotion)) >> promotion;
}
template <class T>
ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CLZ inline
typename std::enable_if<std::is_unsigned<T>::value, T>::type
BitCeilNonPowerOf2(T x) {
// If T is narrower than unsigned, it undergoes promotion to unsigned when we
// shift. We calcualte the number of bits added by the wider type.
return BitCeilPromotionHelper(
static_cast<T>(std::numeric_limits<T>::digits - CountLeadingZeroes(x)),
T{sizeof(T) >= sizeof(unsigned) ? 0
: std::numeric_limits<unsigned>::digits -
std::numeric_limits<T>::digits});
}
} // namespace numeric_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_NUMERIC_INTERNAL_BITS_H_