cpython/Include/internal/pycore_byteswap.h

/* Bytes swap functions, reverse order of bytes:

   - _Py_bswap16(uint16_t)
   - _Py_bswap32(uint32_t)
   - _Py_bswap64(uint64_t)
*/

#ifndef Py_INTERNAL_BSWAP_H
#define Py_INTERNAL_BSWAP_H
#ifdef __cplusplus
extern "C" {
#endif

#ifndef Py_BUILD_CORE
#  error "this header requires Py_BUILD_CORE define"
#endif

#if ((defined(__GNUC__) \
      && ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 8))) \
     || (defined(__clang__) \
         && (__clang_major__ >= 4 \
             || (__clang_major__ == 3 && __clang_minor__ >= 2))))
   /* __builtin_bswap16() is available since GCC 4.8 and clang 3.2,
      __builtin_bswap32() is available since GCC 4.3,
      __builtin_bswap64() is available since GCC 4.3. */
#  define _PY_HAVE_BUILTIN_BSWAP
#endif

#ifdef _MSC_VER
   /* Get _byteswap_ushort(), _byteswap_ulong(), _byteswap_uint64() */
#  include <intrin.h>
#endif

static inline uint16_t
_Py_bswap16(uint16_t word)
{
#ifdef _PY_HAVE_BUILTIN_BSWAP
    return __builtin_bswap16(word);
#elif defined(_MSC_VER)
    Py_BUILD_ASSERT(sizeof(word) == sizeof(unsigned short));
    return _byteswap_ushort(word);
#else
    // Portable implementation which doesn't rely on circular bit shift
    return ( ((word & UINT16_C(0x00FF)) << 8)
           | ((word & UINT16_C(0xFF00)) >> 8));
#endif
}

static inline uint32_t
_Py_bswap32(uint32_t word)
{
#ifdef _PY_HAVE_BUILTIN_BSWAP
    return __builtin_bswap32(word);
#elif defined(_MSC_VER)
    Py_BUILD_ASSERT(sizeof(word) == sizeof(unsigned long));
    return _byteswap_ulong(word);
#else
    // Portable implementation which doesn't rely on circular bit shift
    return ( ((word & UINT32_C(0x000000FF)) << 24)
           | ((word & UINT32_C(0x0000FF00)) <<  8)
           | ((word & UINT32_C(0x00FF0000)) >>  8)
           | ((word & UINT32_C(0xFF000000)) >> 24));
#endif
}

static inline uint64_t
_Py_bswap64(uint64_t word)
{
#ifdef _PY_HAVE_BUILTIN_BSWAP
    return __builtin_bswap64(word);
#elif defined(_MSC_VER)
    return _byteswap_uint64(word);
#else
    // Portable implementation which doesn't rely on circular bit shift
    return ( ((word & UINT64_C(0x00000000000000FF)) << 56)
           | ((word & UINT64_C(0x000000000000FF00)) << 40)
           | ((word & UINT64_C(0x0000000000FF0000)) << 24)
           | ((word & UINT64_C(0x00000000FF000000)) <<  8)
           | ((word & UINT64_C(0x000000FF00000000)) >>  8)
           | ((word & UINT64_C(0x0000FF0000000000)) >> 24)
           | ((word & UINT64_C(0x00FF000000000000)) >> 40)
           | ((word & UINT64_C(0xFF00000000000000)) >> 56));
#endif
}


#ifdef __cplusplus
}
#endif
#endif /* !Py_INTERNAL_BSWAP_H */