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