| … | |
… | |
| 45 | * it works ;) |
45 | * it works ;) |
| 46 | */ |
46 | */ |
| 47 | #ifndef FRST |
47 | #ifndef FRST |
| 48 | # define FRST(p) (((p[0]) << 8) | p[1]) |
48 | # define FRST(p) (((p[0]) << 8) | p[1]) |
| 49 | # define NEXT(v,p) (((v) << 8) | p[2]) |
49 | # define NEXT(v,p) (((v) << 8) | p[2]) |
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50 | # if MULTIPLICATION_IS_SLOW |
| 50 | # if ULTRA_FAST |
51 | # if ULTRA_FAST |
| 51 | # define IDX(h) ((( h >> (3*8 - HLOG)) - h ) & (HSIZE - 1)) |
52 | # define IDX(h) ((( h >> (3*8 - HLOG)) - h ) & (HSIZE - 1)) |
| 52 | # elif VERY_FAST |
53 | # elif VERY_FAST |
| 53 | # define IDX(h) ((( h >> (3*8 - HLOG)) - h*5) & (HSIZE - 1)) |
54 | # define IDX(h) ((( h >> (3*8 - HLOG)) - h*5) & (HSIZE - 1)) |
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55 | # else |
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56 | # define IDX(h) ((((h ^ (h << 5)) >> (3*8 - HLOG)) - h*5) & (HSIZE - 1)) |
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57 | # endif |
| 54 | # else |
58 | # else |
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59 | /* this one was developed with sesse, |
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60 | * and is very similar to the one in snappy. |
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61 | * it does need a modern enough cpu with a fast multiplication. |
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62 | */ |
| 55 | # define IDX(h) ((((h ^ (h << 5)) >> (3*8 - HLOG)) - h*5) & (HSIZE - 1)) |
63 | # define IDX(h) (((h * 0x1e35a7bdU) >> (32 - HLOG - 8)) & (HSIZE - 1)) |
| 56 | # endif |
64 | # endif |
| 57 | #endif |
65 | #endif |
| 58 | /* |
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| 59 | * IDX works because it is very similar to a multiplicative hash, e.g. |
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| 60 | * ((h * 57321 >> (3*8 - HLOG)) & (HSIZE - 1)) |
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| 61 | * the latter is also quite fast on newer CPUs, and compresses similarly. |
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| 62 | * |
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| 63 | * the next one is also quite good, albeit slow ;) |
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| 64 | * (int)(cos(h & 0xffffff) * 1e6) |
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| 65 | */ |
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| 66 | |
66 | |
| 67 | #if 0 |
67 | #if 0 |
| 68 | /* original lzv-like hash function, much worse and thus slower */ |
68 | /* original lzv-like hash function, much worse and thus slower */ |
| 69 | # define FRST(p) (p[0] << 5) ^ p[1] |
69 | # define FRST(p) (p[0] << 5) ^ p[1] |
| 70 | # define NEXT(v,p) ((v) << 5) ^ p[2] |
70 | # define NEXT(v,p) ((v) << 5) ^ p[2] |
