mayhem-firmware/firmware/common/random.cpp
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C++

/*
* Copyright (C) 2023 Bernd Herzog
*
* This file is part of PortaPack.
*
* 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 2, 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; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#include "random.hpp"
static unsigned long state[N]; /* the array for the state vector */
static int rnd_left = 1;
static int rnd_init = 0;
static unsigned long* rnd_next;
/* initializes state[N] with a seed */
void init_genrand(unsigned long s) {
int j;
state[0] = s & 0xffffffffUL;
for (j = 1; j < N; j++) {
state[j] = (1812433253UL * (state[j - 1] ^ (state[j - 1] >> 30)) + j);
/* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
/* In the previous versions, MSBs of the seed affect */
/* only MSBs of the array state[]. */
/* 2002/01/09 modified by Makoto Matsumoto */
state[j] &= 0xffffffffUL; /* for >32 bit machines */
}
rnd_left = 1;
rnd_init = 1;
}
static void next_state(void) {
unsigned long* p = state;
int j;
/* if init_genrand() has not been called, */
/* a default initial seed is used */
if (rnd_init == 0)
init_genrand(5489UL);
rnd_left = N;
rnd_next = state;
for (j = N - M + 1; --j; p++)
*p = p[M] ^ TWIST(p[0], p[1]);
for (j = M; --j; p++)
*p = p[M - N] ^ TWIST(p[0], p[1]);
*p = p[M - N] ^ TWIST(p[0], state[0]);
}
long genrand_int31(void) {
unsigned long y;
if (--rnd_left == 0)
next_state();
y = *rnd_next++;
/* Tempering */
y ^= (y >> 11);
y ^= (y << 7) & 0x9d2c5680UL;
y ^= (y << 15) & 0xefc60000UL;
y ^= (y >> 18);
return (long)(y >> 1);
}