byteswap.h

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// Copyright (c) 2014-2016 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
#ifndef BITCOIN_COMPAT_BYTESWAP_H
#define BITCOIN_COMPAT_BYTESWAP_H
 
#include <cstdint>
#ifdef _MSC_VER
#include <cstdlib>
#endif
 
// All internal_bswap_* functions can be replaced with std::byteswap once we
// require c++23. Both libstdc++ and libc++ implement std::byteswap via these
// builtins.
 
#ifndef DISABLE_BUILTIN_BSWAPS
#if defined __has_builtin
#if __has_builtin(__builtin_bswap16)
#define bitcoin_builtin_bswap16(x) __builtin_bswap16(x)
#endif
#if __has_builtin(__builtin_bswap32)
#define bitcoin_builtin_bswap32(x) __builtin_bswap32(x)
#endif
#if __has_builtin(__builtin_bswap64)
#define bitcoin_builtin_bswap64(x) __builtin_bswap64(x)
#endif
#elif defined(_MSC_VER)
#define bitcoin_builtin_bswap16(x) _byteswap_ushort(x)
#define bitcoin_builtin_bswap32(x) _byteswap_ulong(x)
#define bitcoin_builtin_bswap64(x) _byteswap_uint64(x)
#endif
#endif
 
// MSVC's _byteswap_* functions are not constexpr
 
#ifndef _MSC_VER
#define BSWAP_CONSTEXPR constexpr
#else
#define BSWAP_CONSTEXPR
#endif
 
inline BSWAP_CONSTEXPR uint16_t internal_bswap_16(uint16_t x) {
#ifdef bitcoin_builtin_bswap16
    return bitcoin_builtin_bswap16(x);
#else
    return (x >> 8) | (x << 8);
#endif
}
 
inline BSWAP_CONSTEXPR uint32_t internal_bswap_32(uint32_t x) {
#ifdef bitcoin_builtin_bswap32
    return bitcoin_builtin_bswap32(x);
#else
    return (((x & 0xff000000U) >> 24) | ((x & 0x00ff0000U) >> 8) |
            ((x & 0x0000ff00U) << 8) | ((x & 0x000000ffU) << 24));
#endif
}
 
inline BSWAP_CONSTEXPR uint64_t internal_bswap_64(uint64_t x) {
#ifdef bitcoin_builtin_bswap64
    return bitcoin_builtin_bswap64(x);
#else
    return (((x & 0xff00000000000000ull) >> 56) |
            ((x & 0x00ff000000000000ull) >> 40) |
            ((x & 0x0000ff0000000000ull) >> 24) |
            ((x & 0x000000ff00000000ull) >> 8) |
            ((x & 0x00000000ff000000ull) << 8) |
            ((x & 0x0000000000ff0000ull) << 24) |
            ((x & 0x000000000000ff00ull) << 40) |
            ((x & 0x00000000000000ffull) << 56));
#endif
}
 
#endif // BITCOIN_COMPAT_BYTESWAP_H