98 lines
2.6 KiB
C
98 lines
2.6 KiB
C
/* rand.c -- drand48 implementation from the FreeBSD source tree. */
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// This file is an amalgamation of the many small files in FreeBSD to do with
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// drand48 and friends implementations.
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// It comprises _rand48.c, rand48.h, srand48.c, drand48.c, erand48.c, lrand48.c
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/*
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* Copyright (c) 1993 Martin Birgmeier
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* All rights reserved.
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*
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* You may redistribute unmodified or modified versions of this source
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* code provided that the above copyright notice and this and the
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* following conditions are retained.
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*
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* This software is provided ``as is'', and comes with no warranties
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* of any kind. I shall in no event be liable for anything that happens
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* to anyone/anything when using this software.
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*/
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//#include <sys/cdefs.h>
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//__FBSDID("$FreeBSD: src/lib/libc/gen/_rand48.c,v 1.2 2002/03/22 21:52:05 obrien Exp $");
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#include <math.h>
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#define RAND48_SEED_0 (0x330e)
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#define RAND48_SEED_1 (0xabcd)
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#define RAND48_SEED_2 (0x1234)
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#define RAND48_MULT_0 (0xe66d)
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#define RAND48_MULT_1 (0xdeec)
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#define RAND48_MULT_2 (0x0005)
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#define RAND48_ADD (0x000b)
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static unsigned short _rand48_seed[3] = {
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RAND48_SEED_0,
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RAND48_SEED_1,
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RAND48_SEED_2
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};
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static unsigned short _rand48_mult[3] = {
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RAND48_MULT_0,
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RAND48_MULT_1,
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RAND48_MULT_2
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};
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static unsigned short _rand48_add = RAND48_ADD;
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static void
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_dorand48(unsigned short xseed[3])
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{
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unsigned long accu;
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unsigned short temp[2];
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accu = (unsigned long) _rand48_mult[0] * (unsigned long) xseed[0] +
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(unsigned long) _rand48_add;
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temp[0] = (unsigned short) accu; /* lower 16 bits */
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accu >>= sizeof(unsigned short) * 8;
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accu += (unsigned long) _rand48_mult[0] * (unsigned long) xseed[1] +
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(unsigned long) _rand48_mult[1] * (unsigned long) xseed[0];
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temp[1] = (unsigned short) accu; /* middle 16 bits */
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accu >>= sizeof(unsigned short) * 8;
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accu += _rand48_mult[0] * xseed[2] + _rand48_mult[1] * xseed[1] + _rand48_mult[2] * xseed[0];
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xseed[0] = temp[0];
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xseed[1] = temp[1];
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xseed[2] = (unsigned short) accu;
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}
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HTSLIB_EXPORT
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void hts_srand48(long seed)
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{
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_rand48_seed[0] = RAND48_SEED_0;
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_rand48_seed[1] = (unsigned short) seed;
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_rand48_seed[2] = (unsigned short) (seed >> 16);
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_rand48_mult[0] = RAND48_MULT_0;
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_rand48_mult[1] = RAND48_MULT_1;
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_rand48_mult[2] = RAND48_MULT_2;
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_rand48_add = RAND48_ADD;
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}
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HTSLIB_EXPORT
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double hts_erand48(unsigned short xseed[3])
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{
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_dorand48(xseed);
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return ldexp((double) xseed[0], -48) +
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ldexp((double) xseed[1], -32) +
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ldexp((double) xseed[2], -16);
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}
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HTSLIB_EXPORT
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double hts_drand48(void)
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{
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return hts_erand48(_rand48_seed);
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}
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HTSLIB_EXPORT
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long hts_lrand48(void)
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{
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_dorand48(_rand48_seed);
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return ((long) _rand48_seed[2] << 15) + ((long) _rand48_seed[1] >> 1);
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}
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