/*
* Simple random number generator for testing.
* Copyright © 2022-2024 Nick Bowler
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see .
*
* The RNG implementation is adapted from xoshiro256+ and splitmix64
* by David Blackman and Sebastiano Vigna, originally distributed under
* the Creative Commons Zero public domain dedication.
*/
#include
#include
#include
#include
#include
#include
#include
#if !TEST_RNG_NO_EXTERNAL_API
# include "test.h"
#endif
#define B64(x) ((x) & 0xffffffffffffffffull)
struct test_rng {
unsigned long long state[4];
};
/* Rotate val left by n bits. The behaviour is undefined if n is zero. */
static unsigned long long rot_left64(unsigned long long val, int n)
{
return B64( (val << n) | (val >> (64 - n)) );
}
static unsigned long long xoshiro256p(unsigned long long *s)
{
unsigned long long tmp, ret;
ret = B64(s[0] + s[3]);
tmp = B64(s[1] << 17);
s[2] ^= s[0];
s[3] ^= s[1];
s[1] ^= s[2];
s[0] ^= s[3];
s[2] ^= tmp;
s[3] = rot_left64(s[3], 45);
return ret;
}
static unsigned long long splitmix64(unsigned long long *state)
{
unsigned long long z;
z = B64(*state += 0x9e3779b97f4a7c15ull);
z = B64((z ^ (z >> 30)) * 0xbf58476d1ce4e5b9ull);
z = B64((z ^ (z >> 27)) * 0x94d049bb133111ebull);
return z ^ (z >> 31);
}
#if !TEST_RNG_NO_EXTERNAL_API
struct test_rng *test_rng_alloc(const char *seed_str)
{
unsigned long long seed;
uintmax_t limit, seed_val;
struct test_rng *rng;
limit = (uintmax_t)0xffffffff;
limit |= (limit << 16 << 16);
if (!test_strtoumax(&seed_val, seed_str, limit)) {
print_error("%s: invalid seed", seed_str);
return NULL;
}
seed = seed_val;
rng = malloc_nofail(sizeof *rng);
rng->state[0] = splitmix64(&seed);
rng->state[1] = splitmix64(&seed);
rng->state[2] = splitmix64(&seed);
rng->state[3] = splitmix64(&seed);
return rng;
}
void test_rng_free(struct test_rng *rng)
{
free(rng);
}
/* Calculate the least power of two greater than val, minus 1. */
static unsigned rng_mask(unsigned val)
{
val |= val >> 1;
val |= val >> 2;
val |= val >> 4;
val |= val >> 8;
if (UINT_MAX >= 65536)
val |= val >> 16;
return val;
}
unsigned test_rng_uniform_int(struct test_rng *rng, unsigned max)
{
unsigned mask = rng_mask(max-1);
unsigned long long val;
do {
val = ( xoshiro256p(rng->state) >> 32 ) & mask;
} while (val >= max);
return val;
}
#endif