* chance.c: Roll dice
*
* Known contributors to this file:
- *
+ * Markus Armbruster, 2006-2012
*/
#include <config.h>
#include <math.h>
#include <stdlib.h>
#include "chance.h"
+#include "mt19937ar.h"
/*
* Return non-zero with probability D.
int
chance(double d)
{
- return d > (random() % 32768) / 32768.0;
+ return d > genrand_real2();
+}
+
+/*
+ * Return non-zero with probability PCT%.
+ */
+int
+pct_chance(int pct)
+{
+ return roll(100) <= pct;
+}
+
+static unsigned
+round_up_to_pow2(unsigned val)
+{
+ val--;
+ val |= val >> 1;
+ val |= val >> 2;
+ val |= val >> 4;
+ val |= val >> 8;
+ val |= val >> 16;
+ val++;
+ return val;
}
/*
* Return a random number in [0..N-1].
+ * N must be in [1..2^31-1].
*/
int
roll0(int n)
{
- return random() % n;
+ unsigned pow2 = round_up_to_pow2(n);
+ int r;
+
+ do
+ r = genrand_int32() & (pow2 - 1);
+ while (r >= n);
+ return r;
}
/*
* Return a random number in [1..N].
+ * N must be in [0..2^31-1].
*/
int
roll(int n)
{
- return 1 + random() % n;
+ return 1 + roll0(n);
}
/*
void
seed_prng(unsigned seed)
{
- srandom(seed);
+ init_genrand(seed);
}