155 lines
4.0 KiB
C
155 lines
4.0 KiB
C
/* $NetBSD: factor.c,v 1.10 1999/06/20 06:08:14 cgd Exp $ */
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/*
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* Copyright 1997 Piermont Information Systems Inc.
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* All rights reserved.
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*
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* Written by Philip A. Nelson for Piermont Information Systems Inc.
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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
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* are met:
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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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* 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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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed for the NetBSD Project by
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* Piermont Information Systems Inc.
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* 4. The name of Piermont Information Systems Inc. may not be used to endorse
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* or promote products derived from this software without specific prior
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* written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY PIERMONT INFORMATION SYSTEMS INC. ``AS IS''
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL PIERMONT INFORMATION SYSTEMS INC. BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
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* THE POSSIBILITY OF SUCH DAMAGE.
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*
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*/
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/* Prototypes for strict prototyping. */
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#include <sys/cdefs.h>
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#include <stdio.h>
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static void build_primes __P((long max));
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void factor __P((long val, long *fact_list, int fact_size, int *num_fact));
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/*
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* primes - prime table, built to include up to 46345 because
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* sqrt(2^31) = 46340.9500118415
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*
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* building the table instead of storing a precomputed table saves
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* about 19K of space on the binary image.
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*/
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long primes[4800];
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int num_primes = 2;
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static void
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build_primes(max)
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long max;
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{
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long pc;
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int j;
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long rem;
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/*
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* Initialise primes at run-time rather than compile time
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* so it's put in bss rather than data.
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*/
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primes[0] = 2;
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primes[1] = 3;
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for (pc = primes[num_primes-1]; pc < 46345 && pc*pc <= max; pc+=2) {
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j = 0;
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rem = 1;
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while (j < num_primes && primes[j] * primes[j] <= pc) {
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if ((rem = pc % primes[j]) == 0)
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break;
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j++;
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}
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if (rem)
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primes[num_primes++] = pc;
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}
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}
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/* factor: prepare a list of prime factors of val.
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The last number may not be a prime factor is the list is not
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long enough. */
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void
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factor(val, fact_list, fact_size, num_fact)
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long val;
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long *fact_list;
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int fact_size;
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int *num_fact;
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{
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int i;
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/* Check to make sure we have enough primes. */
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build_primes(val);
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i = 0;
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*num_fact = 0;
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while (*num_fact < fact_size-1 && val > 1 && i < num_primes) {
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/* Find the next prime that divides. */
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while (i < num_primes && val % primes[i] != 0) i++;
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/* Put factors in array. */
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while (*num_fact < fact_size-1 && i < num_primes &&
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val % primes[i] == 0) {
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fact_list[(*num_fact)++] = primes[i];
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val /= primes[i];
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}
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}
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if (val > 1)
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fact_list[(*num_fact)++] = val;
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}
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#ifdef TESTING
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#include <stdio.h>
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#include <stdlib.h>
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int
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main(int argc, char **argv)
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{
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long facts[30];
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long val;
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int i, nfact;
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int arg;
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if (argc < 2) {
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fprintf (stderr, "usage: %s numbers\n", argv[0]);
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exit(1);
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}
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/* Factor each arg! */
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for (arg = 1; arg < argc; arg++) {
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val = atol(argv[arg]);
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factor (val, facts, 30, &nfact);
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printf ("%ld:", val);
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for (i = 0; i<nfact; i++)
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printf (" %ld", facts[i]);
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printf ("\n");
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}
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return 0;
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}
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#endif
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