THUAI6/CAPI/cpp/grpc/include/absl/numeric/internal/bits.h

// 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>
#endif

#include "absl/base/attributes.h"
#include "absl/base/config.h"

#if defined(__GNUC__) && !defined(__clang__)
// GCC
#define ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(x) 1
#else
#define ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(x) ABSL_HAVE_BUILTIN(x)
#endif

#if ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_popcountl) && \
    ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__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_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_clz) && \
    ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__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_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__builtin_ctz) && \
    ABSL_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__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_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__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_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__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_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__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_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__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) || defined(_M_ARM64))
            // 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_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__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_NUMERIC_INTERNAL_HAVE_BUILTIN_OR_GCC(__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) || defined(_M_ARM64))
            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 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_