make sure byte swapping is optimal for git
[git/git.git] / compat / bswap.h
CommitLineData
51ea5519
NP
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 */
12static 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