diff options
Diffstat (limited to 'lzf_c.c')
| -rw-r--r-- | lzf_c.c | 26 |
1 files changed, 13 insertions, 13 deletions
@@ -47,22 +47,22 @@ #ifndef FRST # define FRST(p) (((p[0]) << 8) | p[1]) # define NEXT(v,p) (((v) << 8) | p[2]) -# if ULTRA_FAST -# define IDX(h) ((( h >> (3*8 - HLOG)) - h ) & (HSIZE - 1)) -# elif VERY_FAST -# define IDX(h) ((( h >> (3*8 - HLOG)) - h*5) & (HSIZE - 1)) +# if MULTIPLICATION_IS_SLOW +# if ULTRA_FAST +# define IDX(h) ((( h >> (3*8 - HLOG)) - h ) & (HSIZE - 1)) +# elif VERY_FAST +# define IDX(h) ((( h >> (3*8 - HLOG)) - h*5) & (HSIZE - 1)) +# else +# define IDX(h) ((((h ^ (h << 5)) >> (3*8 - HLOG)) - h*5) & (HSIZE - 1)) +# endif # else -# define IDX(h) ((((h ^ (h << 5)) >> (3*8 - HLOG)) - h*5) & (HSIZE - 1)) +/* this one was developed with sesse, + * and is very similar to the one in snappy. + * it does need a modern enough cpu with a fast multiplication. + */ +# define IDX(h) (((h * 0x1e35a7bdU) >> (32 - HLOG - 8)) & (HSIZE - 1)) # endif #endif -/* - * IDX works because it is very similar to a multiplicative hash, e.g. - * ((h * 57321 >> (3*8 - HLOG)) & (HSIZE - 1)) - * the latter is also quite fast on newer CPUs, and compresses similarly. - * - * the next one is also quite good, albeit slow ;) - * (int)(cos(h & 0xffffff) * 1e6) - */ #if 0 /* original lzv-like hash function, much worse and thus slower */ |