compat/bswap.h

   1 /*
   2  * Let's make sure we always have a sane definition for ntohl()/htonl().
   3  * Some libraries define those as a function call, just to perform byte
   4  * shifting, bringing significant overhead to what should be a simple
   5  * operation.
   6  */
   7
   8 /*
   9  * Default version that the compiler ought to optimize properly with
  10  * constant values.
  11  */
  12 static inline uint32_t default_swab32(uint32_t val)
  13 {
  14         return (((val & 0xff000000) >> 24) |
  15                 ((val & 0x00ff0000) >>  8) |
  16                 ((val & 0x0000ff00) <<  8) |
  17                 ((val & 0x000000ff) << 24));
  18 }
  19
  20 #undef bswap32
  21
  22 #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
  23
  24 #define bswap32 git_bswap32
  25 static inline uint32_t git_bswap32(uint32_t x)
  26 {
  27         uint32_t result;
  28         if (__builtin_constant_p(x))
  29                 result = default_swab32(x);
  30         else
  31                 __asm__("bswap %0" : "=r" (result) : "0" (x));
  32         return result;
  33 }
  34
  35 #elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
  36
  37 #include <stdlib.h>
  38
  39 #define bswap32(x) _byteswap_ulong(x)
  40
  41 #endif
  42
  43 #ifdef bswap32
  44
  45 #undef ntohl
  46 #undef htonl
  47 #define ntohl(x) bswap32(x)
  48 #define htonl(x) bswap32(x)
  49
  50 #endif