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/*
Copyright (C) 2025 Mikael Hildenborg
SPDX-License-Identifier: BSD-2-Clause
*/
#include <_ansi.h>
#include <_syslist.h>
#include <errno.h>
#include "atari-gem_errno.h"
#include "atari-traps.h"
/*
Xorshift pseudorandom number generator.
https://en.wikipedia.org/wiki/Xorshift
Inited with random seed.
*/
int getentropy(void *buf, size_t buflen)
{
unsigned int a;
unsigned int state[4];
// Init state
a = trap14_11(); // Atari Random func.
for (int i = 0; i < 4; ++i)
{
// xorshift32
a ^= (a << 13);
a ^= (a >> 17);
a ^= (a << 5);
state[i] = a;
}
for (size_t i = 0; i < buflen; ++i)
{
// xorshift128
unsigned int t = state[3];
unsigned int s = state[0];
state[3] = state[2];
state[2] = state[1];
state[1] = s;
t ^= t << 11;
t ^= t >> 7;
state[0] = t ^ s ^ (s >> 19);
// use lowest byte (could be optimized to adapt to buf len and output whole 32 bits when possible.)
((unsigned char*)buf)[i] = (unsigned char)state[0];
}
return 0;
}
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