105 lines
2.9 KiB
C
105 lines
2.9 KiB
C
/*-------------------------------------------------------------------------
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*
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* erand48.c
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*
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* This file supplies pg_erand48(), pg_lrand48(), and pg_srand48(), which
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* are just like erand48(), lrand48(), and srand48() except that we use
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* our own implementation rather than the one provided by the operating
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* system. We used to test for an operating system version rather than
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* unconditionally using our own, but (1) some versions of Cygwin have a
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* buggy erand48() that always returns zero and (2) as of 2011, glibc's
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* erand48() is strangely coded to be almost-but-not-quite thread-safe,
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* which doesn't matter for the backend but is important for pgbench.
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*
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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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* IDENTIFICATION
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* src/port/erand48.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "c.h"
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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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double
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pg_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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long
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pg_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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void
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pg_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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