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Re: [PATCH] Optimize manual byte swap implementations using the GCC bswap builtin


Hello Andrew,

> Did you check htons() et al?

Nope. But the glibc bswap implementation matches what the kernel
does. Taken from bits/byteswap.h:

/* Swap bytes in 32 bit value.  */
#define __bswap_constant_32(x) \
     ((((x) & 0xff000000u) >> 24) | (((x) & 0x00ff0000u) >>  8) |             \
      (((x) & 0x0000ff00u) <<  8) | (((x) & 0x000000ffu) << 24))

# define __bswap_constant_64(x) \
     ((((x) & 0xff00000000000000ull) >> 56)                                   \
      | (((x) & 0x00ff000000000000ull) >> 40)                                 \
      | (((x) & 0x0000ff0000000000ull) >> 24)                                 \
      | (((x) & 0x000000ff00000000ull) >> 8)                                  \
      | (((x) & 0x00000000ff000000ull) << 8)                                  \
      | (((x) & 0x0000000000ff0000ull) << 24)                                 \
      | (((x) & 0x000000000000ff00ull) << 40)                                 \
      | (((x) & 0x00000000000000ffull) << 56))

Bye,

-Andreas-


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