summaryrefslogtreecommitdiff
path: root/src/prng/random.c
diff options
context:
space:
mode:
Diffstat (limited to 'src/prng/random.c')
-rw-r--r--src/prng/random.c111
1 files changed, 107 insertions, 4 deletions
diff --git a/src/prng/random.c b/src/prng/random.c
index e6b7fd1f..4b2daef2 100644
--- a/src/prng/random.c
+++ b/src/prng/random.c
@@ -1,8 +1,111 @@
+/*
+ * random.c - Copyright © 2011 Szabolcs Nagy
+ * Permission to use, copy, modify, and/or distribute this code
+ * for any purpose with or without fee is hereby granted.
+ * There is no warranty.
+*/
+
#include <stdlib.h>
+#include <stdint.h>
+
+/*
+this code uses the same lagged fibonacci generator as the
+original bsd random implementation except for the seeding
+
+different seeds produce different sequences with long period
+(other libcs seed the state with a park-miller generator
+when seed=0 some fail to produce good random sequence
+others produce the same sequence as another seed)
+*/
+
+static uint32_t init[] = {
+0x00000000,0x5851f42d,0xc0b18ccf,0xcbb5f646,
+0xc7033129,0x30705b04,0x20fd5db4,0x9a8b7f78,
+0x502959d8,0xab894868,0x6c0356a7,0x88cdb7ff,
+0xb477d43f,0x70a3a52b,0xa8e4baf1,0xfd8341fc,
+0x8ae16fd9,0x742d2f7a,0x0d1f0796,0x76035e09,
+0x40f7702c,0x6fa72ca5,0xaaa84157,0x58a0df74,
+0xc74a0364,0xae533cc4,0x04185faf,0x6de3b115,
+0x0cab8628,0xf043bfa4,0x398150e9,0x37521657};
+
+static int n = 31;
+static int i = 3;
+static int j = 0;
+static uint32_t *x = init+1;
+
+static uint32_t lcg31(uint32_t x) {
+ return (1103515245*x + 12345) & 0x7fffffff;
+}
+
+static uint64_t lcg64(uint64_t x) {
+ return 6364136223846793005ull*x + 1;
+}
+
+static void *savestate() {
+ x[-1] = (n<<16)|(i<<8)|j;
+ return x-1;
+}
+
+static void loadstate(uint32_t *state) {
+ x = state+1;
+ n = x[-1]>>16;
+ i = (x[-1]>>8)&0xff;
+ j = x[-1]&0xff;
+}
+
+void srandom(unsigned seed) {
+ int k;
+ uint64_t s = seed;
+
+ if (n == 0) {
+ x[0] = s;
+ return;
+ }
+ i = n == 31 || n == 7 ? 3 : 1;
+ j = 0;
+ for (k = 0; k < n; k++) {
+ s = lcg64(s);
+ x[k] = s>>32;
+ }
+ /* make sure x contains at least one odd number */
+ x[0] |= 1;
+}
+
+char *initstate(unsigned seed, char *state, size_t size) {
+ void *old = savestate();
+ if (size < 8)
+ return 0;
+ else if (size < 32)
+ n = 0;
+ else if (size < 64)
+ n = 7;
+ else if (size < 128)
+ n = 15;
+ else if (size < 256)
+ n = 31;
+ else
+ n = 63;
+ x = (uint32_t*)state + 1;
+ srandom(seed);
+ return old;
+}
+
+char *setstate(char *state) {
+ void *old = savestate();
+ loadstate((uint32_t*)state);
+ return old;
+}
-/* FIXME */
+long random(void) {
+ long k;
-long random()
-{
- return rand();
+ if (n == 0)
+ return x[0] = lcg31(x[0]);
+ x[i] += x[j];
+ k = x[i]>>1;
+ if (++i == n)
+ i = 0;
+ if (++j == n)
+ j = 0;
+ return k;
}