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/*
* SHR3 - Pseudo random number generator
*
* http://groups.google.com/group/sci.math/msg/9959175f66dd138f
* http://groups.google.com/group/sci.math/msg/7e499231fb1e58d3
*
* Copyright (c) 2020 Michael Buesch <m@bues.ch>
*
* 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 of the License, 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; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "bitops.h"
#include "compat.h"
#include "shr3.h"
#include "util.h"
static uint32_t shr3_state;
uint8_t shr3_get_random_bits(uint8_t nr_of_bits)
{
uint32_t y = shr3_state;
uint8_t ret = 0u;
while (nr_of_bits > 0u) {
y ^= y << 13;
y ^= y >> 17;
y ^= y << 5;
ret = (uint8_t)(ret << 1u);
ret = (uint8_t)(ret | (uint8_t)(y & 1u));
nr_of_bits--;
}
shr3_state = y;
return ret;
}
uint8_t shr3_get_random_value8(uint8_t min_value, uint8_t max_value)
{
uint8_t range, nr_of_bits, value;
range = (uint8_t)(max_value - min_value);
if (range == 0u || min_value > max_value)
return min_value;
nr_of_bits = fls8(range);
do {
value = shr3_get_random_bits(nr_of_bits);
} while (value > range);
value = (uint8_t)(value + min_value);
return value;
}
void shr3_init(uint32_t seed)
{
shr3_state = seed ? seed : 0xFFFFFFFFu;
}
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