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1 | /* |
2 | * Copyright (c) 1980 Regents of the University of California. | |
3 | * All rights reserved. The Berkeley software License Agreement | |
4 | * specifies the terms and conditions for redistribution. | |
5 | */ | |
6 | ||
7 | #ifndef lint | |
8 | char copyright[] = | |
9 | "@(#) Copyright (c) 1980 Regents of the University of California.\n\ | |
10 | All rights reserved.\n"; | |
11 | #endif not lint | |
12 | ||
779464d0 | 13 | #ifndef lint |
e0bbfbf9 DF |
14 | static char sccsid[] = "@(#)primes.c 5.1 (Wollongong) %G%"; |
15 | #endif not lint | |
779464d0 SL |
16 | |
17 | /* | |
18 | * primes [ number ] | |
19 | * | |
20 | * Print all primes greater than argument (or number read from stdin). | |
21 | * | |
22 | * A free translation of 'primes.s' | |
23 | * | |
24 | */ | |
25 | ||
26 | #include <stdio.h> | |
27 | #include <math.h> | |
28 | ||
29 | #define TABSIZE 1000 /* size of sieve table */ | |
30 | #define BIG 4294967296. /* largest unsigned int */ | |
31 | ||
32 | char table[TABSIZE]; /* table for sieve of Eratosthenes */ | |
33 | int tabbits = 8*TABSIZE; /* number of bits in table */ | |
34 | ||
35 | float fstart; | |
36 | unsigned start; /* lowest number to test for prime */ | |
37 | char bittab[] = { /* bit positions (to save shifting) */ | |
38 | 01, 02, 04, 010, 020, 040, 0100, 0200 | |
39 | }; | |
40 | ||
41 | unsigned pt[] = { /* primes < 100 */ | |
42 | 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, | |
43 | 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97 | |
44 | }; | |
45 | ||
46 | unsigned factab[] = { /* difference between succesive trial factors */ | |
47 | 10, 2, 4, 2, 4, 6, 2, 6, 4, 2, 4, 6, 6, 2, 6, 4, | |
48 | 2, 6, 4, 6, 8, 4, 2, 4, 2, 4, 8, 6, 4, 6, 2, 4, | |
49 | 6, 2, 6, 6, 4, 2, 4, 6, 2, 6, 4, 2, 4, 2, 10, 2 | |
50 | }; | |
51 | ||
52 | main(argc, argv) | |
53 | int argc; | |
54 | char **argv; | |
55 | { | |
56 | register unsigned *fp; | |
57 | register char *p; | |
58 | register int i; | |
59 | unsigned quot; | |
60 | unsigned factor, v; | |
61 | ||
62 | if (argc >= 2) { /* get starting no. from arg */ | |
63 | if (sscanf(argv[1], "%f", &fstart) != 1 | |
64 | || fstart < 0.0 || fstart >= BIG) { | |
65 | ouch(); | |
66 | exit(1); | |
67 | } | |
68 | } else { /* get starting no. from stdin */ | |
69 | while ((i = scanf("%f", &fstart)) != 1 | |
70 | || fstart < 0.0 || fstart >= BIG) { | |
71 | if (i == EOF) | |
72 | exit(1); | |
73 | ouch(); | |
74 | } | |
75 | } | |
76 | start = (unsigned)fstart; | |
77 | ||
78 | /* | |
79 | * Quick list of primes < 100 | |
80 | */ | |
81 | if (start <= 97) { | |
82 | for (fp = pt; *fp < start; fp++) | |
83 | ; | |
84 | do | |
85 | printf("%u\n", *fp); | |
86 | while (++fp < &pt[sizeof(pt) / sizeof(*pt)]); | |
87 | start = 100; | |
88 | } | |
89 | quot = start/2; | |
90 | start = quot * 2 + 1; | |
91 | ||
92 | /* | |
93 | * Loop forever: | |
94 | */ | |
95 | for (;;) { | |
96 | /* | |
97 | * Generate primes via sieve of Eratosthenes | |
98 | */ | |
99 | for (p = table; p < &table[TABSIZE]; p++) /* clear sieve */ | |
100 | *p = '\0'; | |
101 | v = (unsigned)sqrt((float)(start + tabbits)); /* highest useful factor */ | |
102 | sieve(3); | |
103 | sieve(5); | |
104 | sieve(7); | |
105 | factor = 11; | |
106 | fp = &factab[1]; | |
107 | do { | |
108 | sieve(factor); | |
109 | factor += *fp; | |
110 | if (++fp >= &factab[sizeof(factab) / sizeof(*factab)]) | |
111 | fp = factab; | |
112 | } while (factor <= v); | |
113 | /* | |
114 | * Print generated primes | |
115 | */ | |
116 | for (i = 0; i < 8*TABSIZE; i += 2) { | |
117 | if ((table[i>>3] & bittab[i&07]) == 0) | |
118 | printf("%u\n", start); | |
119 | start += 2; | |
120 | } | |
121 | } | |
122 | } | |
123 | ||
124 | /* | |
125 | * Insert all multiples of given factor into the sieve | |
126 | */ | |
127 | sieve(factor) | |
128 | unsigned factor; | |
129 | { | |
130 | register int i; | |
131 | unsigned off; | |
132 | unsigned quot; | |
133 | ||
134 | quot = start / factor; | |
135 | off = (quot * factor) - start; | |
136 | if ((int)off < 0) | |
137 | off += factor; | |
138 | while (off < tabbits ) { | |
139 | i = (int)off; | |
140 | table[i>>3] |= bittab[i&07]; | |
141 | off += factor; | |
142 | } | |
143 | } | |
144 | ||
145 | /* | |
146 | * Error message | |
147 | */ | |
148 | ouch() | |
149 | { | |
150 | fprintf(stderr, "Ouch.\n"); | |
151 | } |