58 lines
1.9 KiB
C
58 lines
1.9 KiB
C
/*-------------------------------------------------------------------------
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rand.c - random number generator
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Copyright (C) 2017, Philipp Klaus Krause, pkk@spth.de
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This library is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 2, or (at your option) any
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later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this library; see the file COPYING. If not, write to the
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Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA.
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As a special exception, if you link this library with other files,
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some of which are compiled with SDCC, to produce an executable,
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this library does not by itself cause the resulting executable to
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be covered by the GNU General Public License. This exception does
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not however invalidate any other reasons why the executable file
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might be covered by the GNU General Public License.
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This is an xorshift PRNG. See George Marsaglia, "Xorshift RNGs" for details.
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The width of 32 bits was chosen to not regress in period length vs. the
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PRNG from the C standard, while at the same time minimizing RAM usage.
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The parameters a, b, c were chosen to allow the generation of efficient code.
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-------------------------------------------------------------------------*/
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#include <stdlib.h>
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#include <stdint.h>
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static uint32_t s = 0x80000001;
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int rand(void)
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{
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register unsigned long t = s;
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t ^= t >> 10;
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t ^= t << 9;
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t ^= t >> 25;
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s = t;
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return(t & RAND_MAX);
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}
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void srand(unsigned int seed)
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{
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s = seed | 0x80000000; /* s shall not become 0 */
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}
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