/*-*- 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│
╚──────────────────────────────────────────────────────────────────────────────╝
│                                                                              │
│  Musl Libc                                                                   │
│  Copyright © 2005-2014 Rich Felker, et al.                                   │
│                                                                              │
│  Permission is hereby granted, free of charge, to any person obtaining       │
│  a copy of this software and associated documentation files (the             │
│  "Software"), to deal in the Software without restriction, including         │
│  without limitation the rights to use, copy, modify, merge, publish,         │
│  distribute, sublicense, and/or sell copies of the Software, and to          │
│  permit persons to whom the Software is furnished to do so, subject to       │
│  the following conditions:                                                   │
│                                                                              │
│  The above copyright notice and this permission notice shall be              │
│  included in all copies or substantial portions of the Software.             │
│                                                                              │
│  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,             │
│  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF          │
│  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.      │
│  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY        │
│  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,        │
│  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE           │
│  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                      │
│                                                                              │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/rand/rand.h"

asm(".ident\t\"\\n\\n\
Musl libc (MIT License)\\n\
Copyright 2005-2014 Rich Felker, et. al.\"");
asm(".include \"libc/disclaimer.inc\"");

/*
 * this code uses the same lagged fibonacci generator as the
 * original bsd random implementation except for the seeding
 * which was broken in the original
 */

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(void) {
  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) {
    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;
  if (size < 8) return 0;
  old = savestate();
  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);
  savestate();
  return old;
}

char *setstate(char *state) {
  void *old;
  old = savestate();
  loadstate((uint32_t *)state);
  return old;
}

long random(void) {
  long k;
  if (!n) 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;
}
