| … | |
… | |
| 46 | * the hashing function might seem strange, just believe me |
46 | * the hashing function might seem strange, just believe me |
| 47 | * it works ;) |
47 | * it works ;) |
| 48 | */ |
48 | */ |
| 49 | #define FRST(p) (((p[0]) << 8) + p[1]) |
49 | #define FRST(p) (((p[0]) << 8) + p[1]) |
| 50 | #define NEXT(v,p) (((v) << 8) + p[2]) |
50 | #define NEXT(v,p) (((v) << 8) + p[2]) |
| 51 | #define IDX(h) ((((h ^ (h << 5)) >> (3*8 - HLOG)) + h*3) & (HSIZE - 1)) |
51 | #define IDX(h) ((((h ^ (h << 5)) >> (3*8 - HLOG)) - h*5) & (HSIZE - 1)) |
| 52 | /* |
52 | /* |
| 53 | * IDX works because it is very similar to a multiplicative hash, e.g. |
53 | * IDX works because it is very similar to a multiplicative hash, e.g. |
| 54 | * (h * 57321 >> (3*8 - HLOG)) |
54 | * ((h * 57321 >> (3*8 - HLOG)) & (HSIZE - 1)) |
|
|
55 | * the latter is also quite fast on newer CPUs, and sligthly better |
|
|
56 | * |
| 55 | * the next one is also quite good, albeit slow ;) |
57 | * the next one is also quite good, albeit slow ;) |
| 56 | * (int)(cos(h & 0xffffff) * 1e6) |
58 | * (int)(cos(h & 0xffffff) * 1e6) |
| 57 | */ |
59 | */ |
| 58 | |
60 | |
| 59 | #if 0 |
61 | #if 0 |
| 60 | /* original lzv-like hash function */ |
62 | /* original lzv-like hash function, much worse and thus slower */ |
| 61 | # define FRST(p) (p[0] << 5) ^ p[1] |
63 | # define FRST(p) (p[0] << 5) ^ p[1] |
| 62 | # define NEXT(v,p) ((v) << 5) ^ p[2] |
64 | # define NEXT(v,p) ((v) << 5) ^ p[2] |
| 63 | # define IDX(h) ((h) & (HSIZE - 1)) |
65 | # define IDX(h) ((h) & (HSIZE - 1)) |
| 64 | #endif |
66 | #endif |
| 65 | |
67 | |
