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Justine Tunney 2020-06-15 07:18:57 -07:00
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libc/rand/rngset.c Normal file
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/*-*- 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 2020 Justine Alexandra Roberts Tunney │
│ │
│ 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; version 2 of the License. │
│ │
│ 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, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/rand/rand.h"
#include "libc/rand/xorshift.h"
#include "libc/str/str.h"
/**
* Fills memory with random bytes.
*
* @param seed can be rand64
* @param reseed is number of bytes between seed() calls
* @return buf
*/
void *rngset(void *buf, size_t size, uint64_t (*seed)(void), size_t reseed) {
unsigned char *p;
uint64_t i, x, state;
i = 0;
p = buf;
state = seed();
for (i = 0; size - i >= sizeof(x); i += sizeof(x)) {
x = MarsagliaXorshift64(&state);
memcpy(p + i, &x, sizeof(x));
if (i >= reseed) {
state = seed();
p += i;
size -= i;
i = 0;
}
}
if (i < size) {
x = MarsagliaXorshift64(&state);
for (; i < size; ++i, x >>= 8) {
p[i] = x & 0xff;
}
}
return buf;
}