factor.c - 9base - revived minimalist port of Plan 9 userland to Unix
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factor.c (1348B)
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1 #include <u.h>
2 #include <libc.h>
3 #include <bio.h>
4
5 #define whsiz (sizeof(wheel)/sizeof(wheel[0]))
6
7 double wheel[] =
8 {
9 2,10, 2, 4, 2, 4, 6, 2, 6, 4,
10 2, 4, 6, 6, 2, 6, 4, 2, 6, 4,
11 6, 8, 4, 2, 4, 2, 4, 8, 6, 4,
12 6, 2, 4, 6, 2, 6, 6, 4, 2, 4,
13 6, 2, 6, 4, 2, 4, 2,10,
14 };
15
16 Biobuf bin;
17
18 void factor(double);
19
20 void
21 main(int argc, char *argv[])
22 {
23 double n;
24 int i;
25 char *l;
26
27 if(argc > 1) {
28 for(i=1; i<argc; i++) {
29 n = atof(argv[i]);
30 factor(n);
31 }
32 exits(0);
33 }
34
35 Binit(&bin, 0, OREAD);
36 for(;;) {
37 l = Brdline(&bin, '\n');
38 if(l == 0)
39 break;
40 n = atof(l);
41 if(n <= 0)
42 break;
43 factor(n);
44 }
45 exits(0);
46 }
47
48 void
49 factor(double n)
50 {
51 double quot, d, s;
52 int i;
53
54 print("%.0f\n", n);
55 if(n == 0)
56 return;
57 s = sqrt(n) + 1;
58 while(modf(n/2, ") == 0) {
59 print(" 2\n");
60 n = quot;
61 s = sqrt(n) + 1;
62 }
63 while(modf(n/3, ") == 0) {
64 print(" 3\n");
65 n = quot;
66 s = sqrt(n) + 1;
67 }
68 while(modf(n/5, ") == 0) {
69 print(" 5\n");
70 n = quot;
71 s = sqrt(n) + 1;
72 }
73 while(modf(n/7, ") == 0) {
74 print(" 7\n");
75 n = quot;
76 s = sqrt(n) + 1;
77 }
78 d = 1;
79 for(i=1;;) {
80 d += wheel[i];
81 while(modf(n/d, ") == 0) {
82 print(" %.0f\n", d);
83 n = quot;
84 s = sqrt(n) + 1;
85 }
86 i++;
87 if(i >= whsiz) {
88 i = 0;
89 if(d > s)
90 break;
91 }
92 }
93 if(n > 1)
94 print(" %.0f\n",n);
95 print("\n");
96 }