359 lines
12 KiB
C
359 lines
12 KiB
C
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// Copyright 2020 The Abseil Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef ABSL_NUMERIC_INTERNAL_BITS_H_
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#define ABSL_NUMERIC_INTERNAL_BITS_H_
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#include <cstdint>
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#include <limits>
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#include <type_traits>
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// Clang on Windows has __builtin_clzll; otherwise we need to use the
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// windows intrinsic functions.
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#if defined(_MSC_VER) && !defined(__clang__)
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#include <intrin.h>
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#endif
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#include "absl/base/attributes.h"
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#include "absl/base/config.h"
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#if defined(__GNUC__) && !defined(__clang__)
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// GCC
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#define ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(x) 1
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#else
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#define ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(x) ABSL_HAVE_BUILTIN(x)
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#endif
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#if ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_popcountl) && \
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ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_popcountll)
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#define ABSL_INTERNAL_CONSTEXPR_POPCOUNT constexpr
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#define ABSL_INTERNAL_HAS_CONSTEXPR_POPCOUNT 1
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#else
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#define ABSL_INTERNAL_CONSTEXPR_POPCOUNT
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#define ABSL_INTERNAL_HAS_CONSTEXPR_POPCOUNT 0
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#endif
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#if ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_clz) && \
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ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_clzll)
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#define ABSL_INTERNAL_CONSTEXPR_CLZ constexpr
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#define ABSL_INTERNAL_HAS_CONSTEXPR_CLZ 1
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#else
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#define ABSL_INTERNAL_CONSTEXPR_CLZ
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#define ABSL_INTERNAL_HAS_CONSTEXPR_CLZ 0
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#endif
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#if ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_ctz) && \
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ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_ctzll)
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#define ABSL_INTERNAL_CONSTEXPR_CTZ constexpr
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#define ABSL_INTERNAL_HAS_CONSTEXPR_CTZ 1
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#else
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#define ABSL_INTERNAL_CONSTEXPR_CTZ
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#define ABSL_INTERNAL_HAS_CONSTEXPR_CTZ 0
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#endif
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace numeric_internal {
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constexpr bool IsPowerOf2(unsigned int x) noexcept {
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return x != 0 && (x & (x - 1)) == 0;
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}
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template <class T>
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ABSL_MUST_USE_RESULT ABSL_ATTRIBUTE_ALWAYS_INLINE constexpr T RotateRight(
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T x, int s) noexcept {
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static_assert(std::is_unsigned<T>::value, "T must be unsigned");
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static_assert(IsPowerOf2(std::numeric_limits<T>::digits),
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"T must have a power-of-2 size");
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return static_cast<T>(x >> (s & (std::numeric_limits<T>::digits - 1))) |
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static_cast<T>(x << ((-s) & (std::numeric_limits<T>::digits - 1)));
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}
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template <class T>
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ABSL_MUST_USE_RESULT ABSL_ATTRIBUTE_ALWAYS_INLINE constexpr T RotateLeft(
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T x, int s) noexcept {
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static_assert(std::is_unsigned<T>::value, "T must be unsigned");
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static_assert(IsPowerOf2(std::numeric_limits<T>::digits),
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"T must have a power-of-2 size");
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return static_cast<T>(x << (s & (std::numeric_limits<T>::digits - 1))) |
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static_cast<T>(x >> ((-s) & (std::numeric_limits<T>::digits - 1)));
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}
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ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_POPCOUNT inline int
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Popcount32(uint32_t x) noexcept {
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#if ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_popcount)
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static_assert(sizeof(unsigned int) == sizeof(x),
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"__builtin_popcount does not take 32-bit arg");
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return __builtin_popcount(x);
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#else
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x -= ((x >> 1) & 0x55555555);
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x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
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return static_cast<int>((((x + (x >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24);
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#endif
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}
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ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_POPCOUNT inline int
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Popcount64(uint64_t x) noexcept {
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#if ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_popcountll)
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static_assert(sizeof(unsigned long long) == sizeof(x), // NOLINT(runtime/int)
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"__builtin_popcount does not take 64-bit arg");
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return __builtin_popcountll(x);
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#else
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x -= (x >> 1) & 0x5555555555555555ULL;
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x = ((x >> 2) & 0x3333333333333333ULL) + (x & 0x3333333333333333ULL);
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return static_cast<int>(
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(((x + (x >> 4)) & 0xF0F0F0F0F0F0F0FULL) * 0x101010101010101ULL) >> 56);
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#endif
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}
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template <class T>
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ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_POPCOUNT inline int
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Popcount(T x) noexcept {
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static_assert(std::is_unsigned<T>::value, "T must be unsigned");
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static_assert(IsPowerOf2(std::numeric_limits<T>::digits),
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"T must have a power-of-2 size");
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static_assert(sizeof(x) <= sizeof(uint64_t), "T is too large");
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return sizeof(x) <= sizeof(uint32_t) ? Popcount32(x) : Popcount64(x);
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}
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ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CLZ inline int
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CountLeadingZeroes32(uint32_t x) {
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#if ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_clz)
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// Use __builtin_clz, which uses the following instructions:
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// x86: bsr, lzcnt
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// ARM64: clz
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// PPC: cntlzd
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static_assert(sizeof(unsigned int) == sizeof(x),
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"__builtin_clz does not take 32-bit arg");
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// Handle 0 as a special case because __builtin_clz(0) is undefined.
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return x == 0 ? 32 : __builtin_clz(x);
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#elif defined(_MSC_VER) && !defined(__clang__)
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unsigned long result = 0; // NOLINT(runtime/int)
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if (_BitScanReverse(&result, x)) {
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return 31 - result;
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}
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return 32;
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#else
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int zeroes = 28;
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if (x >> 16) {
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zeroes -= 16;
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x >>= 16;
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}
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if (x >> 8) {
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zeroes -= 8;
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x >>= 8;
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}
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if (x >> 4) {
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zeroes -= 4;
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x >>= 4;
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}
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return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0"[x] + zeroes;
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#endif
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}
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ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CLZ inline int
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CountLeadingZeroes16(uint16_t x) {
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#if ABSL_HAVE_BUILTIN(__builtin_clzs)
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static_assert(sizeof(unsigned short) == sizeof(x), // NOLINT(runtime/int)
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"__builtin_clzs does not take 16-bit arg");
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return x == 0 ? 16 : __builtin_clzs(x);
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#else
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return CountLeadingZeroes32(x) - 16;
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#endif
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}
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ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CLZ inline int
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CountLeadingZeroes64(uint64_t x) {
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#if ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_clzll)
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// Use __builtin_clzll, which uses the following instructions:
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// x86: bsr, lzcnt
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// ARM64: clz
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// PPC: cntlzd
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static_assert(sizeof(unsigned long long) == sizeof(x), // NOLINT(runtime/int)
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"__builtin_clzll does not take 64-bit arg");
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// Handle 0 as a special case because __builtin_clzll(0) is undefined.
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return x == 0 ? 64 : __builtin_clzll(x);
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#elif defined(_MSC_VER) && !defined(__clang__) && \
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(defined(_M_X64) || defined(_M_ARM64))
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// MSVC does not have __buitin_clzll. Use _BitScanReverse64.
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unsigned long result = 0; // NOLINT(runtime/int)
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if (_BitScanReverse64(&result, x)) {
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return 63 - result;
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}
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return 64;
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#elif defined(_MSC_VER) && !defined(__clang__)
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// MSVC does not have __buitin_clzll. Compose two calls to _BitScanReverse
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unsigned long result = 0; // NOLINT(runtime/int)
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if ((x >> 32) &&
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_BitScanReverse(&result, static_cast<unsigned long>(x >> 32))) {
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return 31 - result;
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}
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if (_BitScanReverse(&result, static_cast<unsigned long>(x))) {
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return 63 - result;
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}
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return 64;
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#else
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int zeroes = 60;
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if (x >> 32) {
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zeroes -= 32;
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x >>= 32;
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}
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if (x >> 16) {
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zeroes -= 16;
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x >>= 16;
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}
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if (x >> 8) {
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zeroes -= 8;
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x >>= 8;
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}
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if (x >> 4) {
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zeroes -= 4;
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x >>= 4;
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}
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return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0"[x] + zeroes;
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#endif
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}
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template <typename T>
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ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CLZ inline int
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CountLeadingZeroes(T x) {
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static_assert(std::is_unsigned<T>::value, "T must be unsigned");
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static_assert(IsPowerOf2(std::numeric_limits<T>::digits),
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"T must have a power-of-2 size");
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static_assert(sizeof(T) <= sizeof(uint64_t), "T too large");
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return sizeof(T) <= sizeof(uint16_t)
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? CountLeadingZeroes16(static_cast<uint16_t>(x)) -
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(std::numeric_limits<uint16_t>::digits -
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std::numeric_limits<T>::digits)
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: (sizeof(T) <= sizeof(uint32_t)
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? CountLeadingZeroes32(static_cast<uint32_t>(x)) -
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(std::numeric_limits<uint32_t>::digits -
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std::numeric_limits<T>::digits)
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: CountLeadingZeroes64(x));
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}
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ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CTZ inline int
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CountTrailingZeroesNonzero32(uint32_t x) {
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#if ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_ctz)
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static_assert(sizeof(unsigned int) == sizeof(x),
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"__builtin_ctz does not take 32-bit arg");
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return __builtin_ctz(x);
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#elif defined(_MSC_VER) && !defined(__clang__)
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unsigned long result = 0; // NOLINT(runtime/int)
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_BitScanForward(&result, x);
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return result;
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#else
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int c = 31;
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x &= ~x + 1;
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if (x & 0x0000FFFF) c -= 16;
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if (x & 0x00FF00FF) c -= 8;
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if (x & 0x0F0F0F0F) c -= 4;
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if (x & 0x33333333) c -= 2;
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if (x & 0x55555555) c -= 1;
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return c;
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#endif
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}
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ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CTZ inline int
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CountTrailingZeroesNonzero64(uint64_t x) {
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#if ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_ctzll)
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static_assert(sizeof(unsigned long long) == sizeof(x), // NOLINT(runtime/int)
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"__builtin_ctzll does not take 64-bit arg");
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return __builtin_ctzll(x);
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#elif defined(_MSC_VER) && !defined(__clang__) && \
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(defined(_M_X64) || defined(_M_ARM64))
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unsigned long result = 0; // NOLINT(runtime/int)
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_BitScanForward64(&result, x);
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return result;
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#elif defined(_MSC_VER) && !defined(__clang__)
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unsigned long result = 0; // NOLINT(runtime/int)
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if (static_cast<uint32_t>(x) == 0) {
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_BitScanForward(&result, static_cast<unsigned long>(x >> 32));
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return result + 32;
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}
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_BitScanForward(&result, static_cast<unsigned long>(x));
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return result;
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#else
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int c = 63;
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x &= ~x + 1;
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if (x & 0x00000000FFFFFFFF) c -= 32;
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if (x & 0x0000FFFF0000FFFF) c -= 16;
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if (x & 0x00FF00FF00FF00FF) c -= 8;
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if (x & 0x0F0F0F0F0F0F0F0F) c -= 4;
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if (x & 0x3333333333333333) c -= 2;
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if (x & 0x5555555555555555) c -= 1;
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return c;
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#endif
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}
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ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CTZ inline int
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CountTrailingZeroesNonzero16(uint16_t x) {
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#if ABSL_HAVE_BUILTIN(__builtin_ctzs)
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static_assert(sizeof(unsigned short) == sizeof(x), // NOLINT(runtime/int)
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"__builtin_ctzs does not take 16-bit arg");
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return __builtin_ctzs(x);
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#else
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return CountTrailingZeroesNonzero32(x);
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#endif
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}
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template <class T>
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ABSL_ATTRIBUTE_ALWAYS_INLINE ABSL_INTERNAL_CONSTEXPR_CTZ inline int
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CountTrailingZeroes(T x) noexcept {
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static_assert(std::is_unsigned<T>::value, "T must be unsigned");
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static_assert(IsPowerOf2(std::numeric_limits<T>::digits),
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"T must have a power-of-2 size");
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static_assert(sizeof(T) <= sizeof(uint64_t), "T too large");
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return x == 0 ? std::numeric_limits<T>::digits
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|
: (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 calculate 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_
|