130 lines
2.5 KiB
C
130 lines
2.5 KiB
C
/*
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* Let's C Version 4.0.C.
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* Copyright (c) 1982-1987 by Mark Williams Company, Chicago.
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* All rights reserved. May not be copied or disclosed without permission.
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*/
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/*
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* Factor prints out the prime factorization of numbers. If there are
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* any arguments, then it factors these. If there are no arguments,
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* then it reads stdin until either EOF or the number zero or a non-numeric
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* non-white-space character. Since factor does all of its calculations
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* in double format, the largest number which can be handled is quite
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* large.
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*/
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#include <stdio.h>
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#include <math.h>
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#include <ctype.h>
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#define NUL '\0'
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#define ERROR 0x10 /* largest input base */
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#define MAXNUM 200 /* max number of chars in number */
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main(argc, argv)
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int argc;
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register char *argv[];
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{
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register char *chp;
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double n;
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double atod();
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char *getnum();
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if (argc != 1)
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while ((chp=*++argv) != NULL && (n=atod(chp)) != 0)
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factor(n);
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else
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while ((chp=getnum()) != NULL && (n=atod(chp)) != 0)
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factor(n);
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return (0);
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}
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die(str)
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char *str;
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{
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fprintf(stderr, "%r\n", &str);
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exit(1);
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}
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usage()
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{
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die("usage: factor [number number ...]");
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}
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char *
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getnum()
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{
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register char *chp,
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ch;
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static char res[MAXNUM+1];
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do {
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ch = getchar();
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} while (isascii(ch) && isspace(ch));
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if (!isascii(ch) || todigit(ch) == ERROR)
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return (NULL);
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for (chp=res; isascii(ch) && !isspace(ch); ch=getchar())
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if (chp < &res[MAXNUM])
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*chp++ = ch;
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if (chp >= &res[MAXNUM])
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die("Number too big");
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*chp++ = NUL;
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return (res);
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}
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/*
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* Todigit converts the char `ch' to an integer equivalent, assuming
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* that `ch' is a digit or `a'-`f' or `A'-`F'. If this is not true,
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* then it returns ERROR.
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*/
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todigit(ch)
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register int ch;
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{
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if (!isascii(ch))
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return (ERROR);
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if (isdigit(ch))
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return (ch - '0' + 0);
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if (isupper(ch))
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ch = tolower(ch);
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if ('a' <= ch && ch <= 'f')
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return (ch - 'a' + 0xa);
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return (ERROR);
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}
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/*
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* Factor is the routine that actually factors the double `n'.
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* It writes the prime factors to standard output.
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*/
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factor(n)
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double n;
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{
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double temp,
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limit,
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try;
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while (n > 1 && modf(n/2, &temp) == 0) {
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printf("2 ");
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n = temp;
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}
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limit = sqrt(n);
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for (try=3; try <= limit; try += 2) {
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if (modf(n/try, &temp) != 0)
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continue;
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do {
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printf("%.0f ", try);
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n = temp;
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} while (modf(n/try, &temp) == 0);
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limit = sqrt(n);
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}
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if (n > 1)
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printf("%.0f", n);
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putchar('\n');
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}
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