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Replace rng_rand_range() with GLib's g_rand_int_range() that works better

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This commit is contained in:
Julien BLACHE 2010-04-30 18:36:51 +02:00
parent 5e9c245e39
commit ffcf100c00
1 changed files with 26 additions and 8 deletions
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34
src/rng.c
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@ -88,22 +88,40 @@ rng_rand(struct rng_ctx *ctx)
return ctx->iy;
}
/* Integer in [min, max[, min >= 0 */
/* Integer in [min, max[ */
/* Taken from GLib 2.0 v2.25.3, g_rand_int_range(), GPLv2+ */
int32_t
rng_rand_range(struct rng_ctx *ctx, int32_t min, int32_t max)
{
int32_t res;
int32_t range;
int32_t dist;
uint32_t maxvalue;
uint32_t leftover;
range = max - min;
dist = max - min;
res = rng_rand(ctx);
res = (int32_t)((double)range * ((1.0 / 2147483647.0) * (double)res));
if (dist <= 0)
return min;
if (min > 0)
res += min;
/* maxvalue is set to the predecessor of the greatest
* multiple of dist less or equal 2^32. */
if (dist <= 0x80000000u) /* 2^31 */
{
/* maxvalue = 2^32 - 1 - (2^32 % dist) */
leftover = (0x80000000u % dist) * 2;
if (leftover >= dist)
leftover -= dist;
maxvalue = 0xffffffffu - leftover;
}
else
maxvalue = dist - 1;
do
res = rng_rand(ctx);
while (res > maxvalue);
return res;
res %= dist;
return min + res;
}
/* Fisher-Yates shuffling algorithm