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rnd(): add notes, and create rnd_verify() to confirm implementation is correct. Copied from Perforce Change: 167181 ServerID: perforce.ravenbrook.com
261 lines
8 KiB
C
261 lines
8 KiB
C
/* testlib.c: TEST LIBRARY
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*
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* $Id$
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* Copyright (c) 2001 Ravenbrook Limited. See end of file for license.
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* Portions copyright (C) 2002 Global Graphics Software.
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*
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* .purpose: A library of functions that may be of use to unit tests.
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*/
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#include "testlib.h"
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#include "mps.h"
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#include "misc.h" /* for NOOP */
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#include <math.h>
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#include <stdlib.h>
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#include <limits.h>
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#ifdef MPS_OS_IA
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struct itimerspec; /* stop complaints from time.h */
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#endif
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#include <time.h>
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#ifdef MPS_BUILD_MV
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/* MSVC warning 4702 = unreachable code
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*
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* job000605: believed needed to prevent VC7 warning
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* for error() below, in which va_end is mandated by
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* ISO C (C99:7.15.1) even though it is unreachable.
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*/
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#pragma warning(disable: 4702)
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/* MSVC warning 4996 = stdio / C runtime 'unsafe' */
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/* Objects to: sscanf. See job001934. */
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#pragma warning( disable : 4996 )
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#endif
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/* rnd -- a random number generator
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*
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* I nabbed it from "ML for the Working Programmer", originally from:
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* Stephen K Park & Keith W Miller (1988). Random number generators:
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* good ones are hard to find. Communications of the ACM, 31:1192-1201.
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*
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* This is a 'full-period' generator: all values from [1..(mod-1)]
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* are returned once, and then the generator cycles round again.
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* (The value 0 is not part of the cycle and is never returned). That
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* means the period = mod-1, ie. 2147483646.
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*
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* This "x 16807 mod 2^31-1" generator has been very well studied.
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* It is not the 'best' (most random) simple generator, but it is
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* free of all vices we might care about for this application, so
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* we'll keep it simple and stick with this, thanks.
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*
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* There are faster implementations of this generator, summarised
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* briefly here:
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* - L. Schrage (1979 & 1983) showed how to do all the calculations
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* within 32-bit integers. See also Numerical recipes in C.
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* - David Carta (1990) showed how to also eliminate division.
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*/
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static unsigned long seed = 1;
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/* 2^31 - 1 == (1UL<<31) - 1 == 2147483647 */
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#define RND_MOD_2_31_1 2147483647
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#define RND_MOD_2_31_1_FLOAT 2147483647.0
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unsigned long rnd(void)
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{
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double s;
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s = seed;
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s *= 16807.0;
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s = fmod(s, RND_MOD_2_31_1_FLOAT); /* 2^31 - 1 */
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seed = (unsigned long)s;
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return seed;
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/* Have you modified this code? Run rnd_verify() please! RHSK */
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}
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/* rnd_verify -- verify that rnd() returns the correct results */
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static void rnd_verify(void)
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{
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unsigned long orig_seed = seed;
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unsigned long i;
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/* This test is from:
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* Stephen K Park & Keith W Miller (1988). Random number generators:
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* good ones are hard to find. Communications of the ACM, 31:1192-1201.
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* Note: The Park-Miller paper uses 1-based indices.
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*/
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i = 1;
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seed = 1;
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for(i = 2; i < 10001; i += 1) {
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(void)rnd();
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}
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Insist(i == 10001);
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Insist(rnd() == 1043618065);
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/* from Robin Whittle's compendium at
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* http://www.firstpr.com.au/dsp/rand31/
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* Observe wrap-around after 'full-period' (which excludes 0).
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* Note: uses 0-based indices, ie. rnd_0 = 1, rnd_1 = 16807, ...
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*/
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i = 2147483645;
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seed = 1407677000;
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i += 1;
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Insist(i == (1UL<<31) - 2 ); /* 'full-period' excludes 0 */
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Insist(rnd() == 1); /* wrap-around */
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seed = orig_seed;
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}
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/* rnd_addr -- a random address generator
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*
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* rnd gives 31 random bits, we run it repeatedly to get enough bits.
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*/
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#define ADDR_BITS (sizeof(mps_addr_t) * CHAR_BIT)
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mps_addr_t rnd_addr(void)
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{
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mps_word_t res;
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unsigned bits;
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for (bits = 0, res = 0; bits < ADDR_BITS;
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bits += 31, res = res << 31 | (mps_word_t)rnd())
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NOOP;
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return (mps_addr_t)res;
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}
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/* randomize -- randomize the generator, or initialize to replay */
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void randomize(int argc, char **argv)
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{
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int n;
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unsigned long seed0;
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int i;
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if (argc > 1) {
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n = sscanf(argv[1], "%lu", &seed0);
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Insist(n == 1);
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printf("randomize(): resetting initial seed to: %lu.\n", seed0);
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rnd_verify(); /* good to verify occasionally: slip it in here */
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} else {
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/* time_t uses an arbitrary encoding, but hopefully the low order */
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/* 31 bits will have at least one bit changed from run to run. */
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seed0 = 1 + time(NULL) % (RND_MOD_2_31_1 - 1);
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printf("randomize(): choosing initial seed: %lu.\n", seed0);
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}
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Insist(seed0 < RND_MOD_2_31_1); /* 2^31 - 1 */
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Insist(seed0 != 0);
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seed = seed0;
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/* The 'random' seed is taken from time(), which may simply be a
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* count of seconds: therefore successive runs may start with
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* nearby seeds, possibly differing only by 1. So the first value
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* returned by rnd() may differ by only 16807. It is conceivable
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* that some tests might be able to 'spot' this pattern (for
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* example: by using the first rnd() value, mod 100M and rounded
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* to multiple of 128K, as arena size).
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*
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* So to mix it up a bit, we do a few iterations now. How many?
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* Very roughly, 16807^2 is of the same order as 2^31, so two
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* iterations would make the characteristic difference similar to
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* the period. Hey, let's go wild and do 10.
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*/
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for(i = 0; i < 10; i += 1) {
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(void)rnd();
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}
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}
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/* verror -- die with message */
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void verror(const char *format, va_list args)
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{
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fflush(stdout); /* synchronize */
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vfprintf(stderr, format, args);
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fprintf(stderr, "\n");
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exit(1);
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}
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/* error -- die with message */
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void error(const char *format, ...)
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{
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va_list args;
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va_start(args, format);
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verror(format, args);
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va_end(args);
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}
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/* die -- Test a return code, and exit on error */
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void die(mps_res_t res, const char *s)
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{
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if (res != MPS_RES_OK) {
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error("\n%s: %d\n", s, res);
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}
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}
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/* die_expect -- Test a return code, and exit on unexpected result */
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void die_expect(mps_res_t res, mps_res_t expected, const char *s)
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{
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if (res != expected) {
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error("\n%s: %d\n", s, res);
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}
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}
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/* cdie -- Test a C boolean, and exit on error */
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void cdie(int res, const char *s)
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{
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if (!res) {
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error("\n%s: %d\n", s, res);
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}
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}
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/* C. COPYRIGHT AND LICENSE
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*
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* Copyright (C) 2001-2002, 2008 Ravenbrook Limited <http://www.ravenbrook.com/>.
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* All rights reserved. This is an open source license. Contact
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* Ravenbrook for commercial licensing options.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* 3. Redistributions in any form must be accompanied by information on how
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* to obtain complete source code for this software and any accompanying
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* software that uses this software. The source code must either be
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* included in the distribution or be available for no more than the cost
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* of distribution plus a nominal fee, and must be freely redistributable
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* under reasonable conditions. For an executable file, complete source
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* code means the source code for all modules it contains. It does not
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* include source code for modules or files that typically accompany the
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* major components of the operating system on which the executable file
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* runs.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
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* PURPOSE, OR NON-INFRINGEMENT, ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT HOLDERS AND CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
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* ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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