54 lines
885 B
C
Executable file
54 lines
885 B
C
Executable file
/* factor - print the prime factors of a number Author: Andy Tanenbaum */
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#include <stdlib.h>
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#include <stdio.h>
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_PROTOTYPE(int main, (int argc, char **argv));
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_PROTOTYPE(long first, (long k));
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int main(argc, argv)
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int argc;
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char *argv[];
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{
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/* Factor a number */
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long i, n, flag = 0;
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if (argc != 2 || (n = atol(argv[1])) < 2) {
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printf("Usage: factor n (2 <= n < 2**31)\n");
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exit(1);
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}
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if (n == 2) {
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printf("2 is a prime\n");
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exit(0);
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}
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while (1) {
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i = first(n);
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if (i == 0) {
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if (flag == 0)
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printf("%ld is a prime\n", n);
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else
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printf("%ld\n", n);
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exit(0);
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}
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printf("%ld ", i);
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n = n / i;
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flag = 1;
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}
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}
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long first(k)
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long k;
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{
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/* Return the first factor of k. If it is a prime, return 0; */
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long i;
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if (k == 2) return(0);
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if (k % 2 == 0) return (2);
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for (i = 3; i <= k / 3; i += 2)
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if (k % i == 0) return(i);
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return(0);
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}
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