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author | Rich Felker <dalias@aerifal.cx> | 2011-06-23 18:02:23 -0400 |
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committer | Rich Felker <dalias@aerifal.cx> | 2011-06-23 18:02:23 -0400 |
commit | c7ce1b20d2f37f97f9cfcd57cb4fb4c7cd66a3a0 (patch) | |
tree | 77a4dae07e3fd48098566d013a2c332053a1b265 /src/prng | |
parent | d19adeec52ee2e5f9524d306576cfd6bfc4a031a (diff) | |
download | musl-c7ce1b20d2f37f97f9cfcd57cb4fb4c7cd66a3a0.zip musl-c7ce1b20d2f37f97f9cfcd57cb4fb4c7cd66a3a0.tar.gz musl-c7ce1b20d2f37f97f9cfcd57cb4fb4c7cd66a3a0.tar.bz2 |
initial commit of prng implementation by Szabolcs Nagy
Diffstat (limited to 'src/prng')
-rw-r--r-- | src/prng/random.c | 111 | ||||
-rw-r--r-- | src/prng/srandom.c | 8 |
2 files changed, 107 insertions, 12 deletions
diff --git a/src/prng/random.c b/src/prng/random.c index e6b7fd1..4b2daef 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; } diff --git a/src/prng/srandom.c b/src/prng/srandom.c deleted file mode 100644 index 77f4dcb..0000000 --- a/src/prng/srandom.c +++ /dev/null @@ -1,8 +0,0 @@ -#include <stdlib.h> - -/* FIXME */ - -void srandom(unsigned seed) -{ - return srand(seed); -} |