* chance.c: Roll dice
*
* Known contributors to this file:
- *
+ * Markus Armbruster, 2006-2012
*/
#include <config.h>
+#include <fcntl.h>
#include <math.h>
+#include <stdint.h>
#include <stdlib.h>
+#include <sys/time.h>
+#include <unistd.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);
+}
+
+static uint32_t
+djb_hash(uint32_t hash, void *buf, size_t sz)
+{
+ unsigned char *bp;
+
+ for (bp = buf; bp < (unsigned char *)buf + sz; bp++)
+ hash = hash * 33 ^ *bp;
+
+ return hash;
+}
+
+/*
+ * Pick a reasonably random seed for the pseudo-random number generator.
+ */
+unsigned
+pick_seed(void)
+{
+ int fd;
+ uint32_t seed;
+ int got_seed = 0;
+ struct timeval tv;
+ pid_t pid;
+
+ /*
+ * Modern systems provide random number devices, but the details
+ * vary. On many systems, /dev/random blocks when the kernel
+ * entropy pool has been depleted, while /dev/urandom doesn't.
+ * The former should only be used for generating long-lived
+ * cryptographic keys. On other systems, both devices behave
+ * exactly the same, or only /dev/random exists.
+ *
+ * Try /dev/urandom first, and if it can't be opened, blindly try
+ * /dev/random.
+ */
+ fd = open("/dev/urandom", O_RDONLY | O_NONBLOCK);
+ if (fd < 0)
+ fd = open("/dev/random", O_RDONLY | O_NONBLOCK);
+ if (fd >= 0) {
+ got_seed = read(fd, &seed, sizeof(seed)) == sizeof(seed);
+ close(fd);
+ }
+
+ if (!got_seed) {
+ /* Kernel didn't provide, fall back to hashing time and PID */
+ gettimeofday(&tv, NULL);
+ seed = djb_hash(5381, &tv, sizeof(tv));
+ pid = getpid();
+ seed = djb_hash(seed, &pid, sizeof(pid));
+ }
+
+ return seed;
}