Add support for normal/gaussian random distributions

[fio.git] / lib / gauss.c

diff --git a/lib/gauss.c b/lib/gauss.c
new file mode 100644 (file)
index 0000000..cd8b6e3
--- /dev/null
+++ b/lib/gauss.c
@@ -0,0 +1,53 @@
+#include <math.h>
+#include <string.h>
+#include <stdio.h>
+#include "../hash.h"
+#include "gauss.h"
+
+#define GAUSS_ITERS    12
+
+static int gauss_dev(struct gauss_state *gs)
+{
+       unsigned int r;
+       int vr;
+
+       if (!gs->stddev)
+               return 0;
+
+       r = __rand(&gs->r);
+       vr = gs->stddev * (r / (FRAND_MAX + 1.0));
+
+       return vr - gs->stddev / 2;
+}
+
+unsigned long long gauss_next(struct gauss_state *gs)
+{
+       unsigned long long sum = 0;
+       int i;
+
+       for (i = 0; i < GAUSS_ITERS; i++)
+               sum += __rand(&gs->r) % (gs->nranges + 1);
+
+       sum = (sum + GAUSS_ITERS - 1) / GAUSS_ITERS;
+
+       if (gs->stddev) {
+               int dev = gauss_dev(gs);
+
+               while (dev + sum >= gs->nranges)
+                       dev /= 2;
+               sum += dev;
+       }
+
+       return __hash_u64(sum) % gs->nranges;
+}
+
+void gauss_init(struct gauss_state *gs, unsigned long nranges, unsigned int d,
+               unsigned int seed)
+{
+       memset(gs, 0, sizeof(*gs));
+       init_rand_seed(&gs->r, seed);
+       gs->nranges = nranges;
+       gs->stddev = d;
+       if (gs->stddev > nranges / 2)
+               gs->stddev = nranges / 2;
+}