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 unsigned int default_swab32(unsigned int val)
  13 {
  14         return (((val & 0xff000000) >> 24) |
  15                 ((val & 0x00ff0000) >>  8) |
  16                 ((val & 0x0000ff00) <<  8) |
  17                 ((val & 0x000000ff) << 24));
  18 }
  19
  20 #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
  21
  22 #define bswap32(x) ({ \
  23         unsigned int __res; \
  24         if (__builtin_constant_p(x)) { \
  25                 __res = default_swab32(x); \
  26         } else { \
  27                 __asm__("bswap %0" : "=r" (__res) : "0" (x)); \
  28         } \
  29         __res; })
  30
  31 #undef ntohl
  32 #undef htonl
  33 #define ntohl(x) bswap32(x)
  34 #define htonl(x) bswap32(x)
  35
  36 #endif