| 1 | #include <math.h> |
| 2 | #include <string.h> |
| 3 | #include "../hash.h" |
| 4 | #include "gauss.h" |
| 5 | |
| 6 | #define GAUSS_ITERS 12 |
| 7 | |
| 8 | static int gauss_dev(struct gauss_state *gs) |
| 9 | { |
| 10 | unsigned int r; |
| 11 | int vr; |
| 12 | |
| 13 | if (!gs->stddev) |
| 14 | return 0; |
| 15 | |
| 16 | r = __rand(&gs->r); |
| 17 | vr = gs->stddev * (r / (FRAND32_MAX + 1.0)); |
| 18 | |
| 19 | return vr - gs->stddev / 2; |
| 20 | } |
| 21 | |
| 22 | unsigned long long gauss_next(struct gauss_state *gs) |
| 23 | { |
| 24 | unsigned long long sum = 0; |
| 25 | int i; |
| 26 | |
| 27 | for (i = 0; i < GAUSS_ITERS; i++) |
| 28 | sum += __rand(&gs->r) % (gs->nranges + 1); |
| 29 | |
| 30 | sum = (sum + GAUSS_ITERS - 1) / GAUSS_ITERS; |
| 31 | |
| 32 | if (gs->stddev) { |
| 33 | int dev = gauss_dev(gs); |
| 34 | |
| 35 | while (dev + sum >= gs->nranges) |
| 36 | dev /= 2; |
| 37 | sum += dev; |
| 38 | } |
| 39 | |
| 40 | if (!gs->disable_hash) |
| 41 | sum = __hash_u64(sum); |
| 42 | |
| 43 | return (sum + gs->rand_off) % gs->nranges; |
| 44 | } |
| 45 | |
| 46 | void gauss_init(struct gauss_state *gs, unsigned long nranges, double dev, |
| 47 | double center, unsigned int seed) |
| 48 | { |
| 49 | memset(gs, 0, sizeof(*gs)); |
| 50 | init_rand_seed(&gs->r, seed, 0); |
| 51 | gs->nranges = nranges; |
| 52 | |
| 53 | if (dev != 0.0) { |
| 54 | gs->stddev = ceil((double)(nranges * dev) / 100.0); |
| 55 | if (gs->stddev > nranges / 2) |
| 56 | gs->stddev = nranges / 2; |
| 57 | } |
| 58 | if (center == -1) |
| 59 | gs->rand_off = 0; |
| 60 | else |
| 61 | gs->rand_off = nranges * (center - 0.5); |
| 62 | } |
| 63 | |
| 64 | void gauss_disable_hash(struct gauss_state *gs) |
| 65 | { |
| 66 | gs->disable_hash = true; |
| 67 | } |