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Allow seeding RNG with a byte sequence.

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This commit is contained in:
Calvin Rose 2019-11-21 22:53:39 -06:00
parent 624f5f428e
commit 02fc4ae27b
2 changed files with 40 additions and 7 deletions
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11
examples/rtest.janet Normal file
View File

@ -0,0 +1,11 @@
# How random is the RNG really?
(def counts (seq [_ :range [0 100]] 0))
(for i 0 1000000
(let [x (math/random)
intrange (math/floor (* 100 x))
oldcount (counts intrange)]
(put counts intrange (if oldcount (+ 1 oldcount) 1))))
(pp counts)

34
src/core/math.c
View File

@ -65,17 +65,30 @@ JanetRNG *janet_default_rng(void) {
} }
void janet_rng_seed(JanetRNG *rng, uint32_t seed) { void janet_rng_seed(JanetRNG *rng, uint32_t seed) {
rng->a = seed + 123573u; rng->a = seed;
rng->b = (seed + 43234283u) % 12391233u; rng->b = 0x97654321u;
rng->c = 0x17af0931u; rng->c = 123871873u;
rng->d = 0xFFFaaFFFu; rng->d = 0xf23f56c8u;
rng->counter = 0u; rng->counter = 0u;
/* First several numbers aren't that random. */ /* First several numbers aren't that random. */
for (int i = 0; i < 16; i++) janet_rng_u32(rng); for (int i = 0; i < 16; i++) janet_rng_u32(rng);
} }
void janet_rng_longseed(JanetRNG *rng, const uint8_t *bytes, int32_t len) {
uint8_t state[16] = {0};
for (int32_t i = 0; i < len; i++)
state[i % 16] ^= bytes[i];
rng->a = state[0] + (state[1] << 8) + (state[2] << 16) + (state[3] << 24);
rng->b = state[4] + (state[5] << 8) + (state[6] << 16) + (state[7] << 24);
rng->c = state[8] + (state[9] << 8) + (state[10] << 16) + (state[11] << 24);
rng->d = state[12] + (state[13] << 8) + (state[14] << 16) + (state[15] << 24);
rng->counter = 0u;
for (int i = 0; i < 16; i++) janet_rng_u32(rng);
}
uint32_t janet_rng_u32(JanetRNG *rng) { uint32_t janet_rng_u32(JanetRNG *rng) {
/* Algorithm "xorwow" from p. 5 of Marsaglia, "Xorshift RNGs" */ /* Algorithm "xorwow" from p. 5 of Marsaglia, "Xorshift RNGs" */
/* Modified to remove constraint that a, b, c, d != 0 */
uint32_t t = rng->d; uint32_t t = rng->d;
uint32_t const s = rng->a; uint32_t const s = rng->a;
rng->d = rng->c; rng->d = rng->c;
@ -84,7 +97,7 @@ uint32_t janet_rng_u32(JanetRNG *rng) {
t ^= t >> 2; t ^= t >> 2;
t ^= t << 1; t ^= t << 1;
t ^= s ^ (s << 4); t ^= s ^ (s << 4);
rng->a = t; rng->a = t + 33;
rng->counter += 362437; rng->counter += 362437;
return t + rng->counter; return t + rng->counter;
} }
@ -98,9 +111,18 @@ double janet_rng_double(JanetRNG *rng) {
static Janet cfun_rng_make(int32_t argc, Janet *argv) { static Janet cfun_rng_make(int32_t argc, Janet *argv) {
janet_arity(argc, 0, 1); janet_arity(argc, 0, 1);
uint32_t seed = (uint32_t)(argc == 1 ? janet_getinteger(argv, 0) : 0);
JanetRNG *rng = janet_abstract(&JanetRNG_type, sizeof(JanetRNG)); JanetRNG *rng = janet_abstract(&JanetRNG_type, sizeof(JanetRNG));
if (argc == 1) {
if (janet_checkint(argv[0])) {
uint32_t seed = (uint32_t)(janet_getinteger(argv, 0));
janet_rng_seed(rng, seed); janet_rng_seed(rng, seed);
} else {
JanetByteView bytes = janet_getbytes(argv, 0);
janet_rng_longseed(rng, bytes.bytes, bytes.len);
}
} else {
janet_rng_seed(rng, 0);
}
return janet_wrap_abstract(rng); return janet_wrap_abstract(rng);
} }