cosmopolitan/libc/rand/vigna.c
Justine Tunney 39bf41f4eb Make numerous improvements
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2021-09-28 01:52:34 -07:00

77 lines
3.3 KiB
C

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2021 Justine Alexandra Roberts Tunney │
│ │
│ Permission to use, copy, modify, and/or distribute this software for │
│ any purpose with or without fee is hereby granted, provided that the │
│ above copyright notice and this permission notice appear in all copies. │
│ │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/bits/xadd.h"
#include "libc/rand/rand.h"
static uint64_t g_vigna;
/**
* Returns deterministic pseudorandom data, e.g.
*
* uint64_t x = vigna();
*
* You can generate different types of numbers as follows:
*
* int64_t x = vigna() >> 1; // make positive signed integer
* double x = _real1(vigna()); // make float on [0,1]-interval
*
* You can seed this random number generator using:
*
* svigna(rdseed());
*
* You may use the reentrant version of this function:
*
* static uint64_t s = 0;
* uint64_t x = svigna_r(&s);
*
* This function is the fastest way to generate good scalar pseudorandom
* numbers that aren't truncated. If you want to fill a buffer with data
* then rngset() implements vigna's algorithm to do that extremely well:
*
* char buf[4096];
* rngset(buf, sizeof(buf), vigna, 0);
*
* If you want a fast pseudorandom number generator that seeds itself
* automatically on startup and fork() then consider rand64(). If you
* want true random data then consider rdseed, rdrand, and getrandom.
*
* @return 64 bits of pseudorandom data
*/
uint64_t vigna(void) {
return vigna_r(&g_vigna);
}
/**
* Returns pseudorandom data.
* @see vigna() for easy api
*/
uint64_t vigna_r(uint64_t state[hasatleast 1]) {
uint64_t z = (state[0] += 0x9e3779b97f4a7c15);
z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
return z ^ (z >> 31);
}
/**
* Seeds vigna() pseudorandom number generator.
* @see vigna(), vigna_r()
*/
void svigna(uint64_t seed) {
g_vigna = seed;
}