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1.1 root 1: /*
2: * Copyright (c) 1989 The Regents of the University of California.
3: * All rights reserved.
4: *
5: * This code is derived from software contributed to Berkeley by
6: * Rick Adams.
7: *
8: * Authors:
9: * Stan King, John Eldridge, based on algorithm suggested by
10: * Bob Morris
11: * 29-Sep-82
12: *
13: * Redistribution and use in source and binary forms are permitted provided
14: * that: (1) source distributions retain this entire copyright notice and
15: * comment, and (2) distributions including binaries display the following
16: * acknowledgement: ``This product includes software developed by the
17: * University of California, Berkeley and its contributors'' in the
18: * documentation or other materials provided with the distribution and in
19: * all advertising materials mentioning features or use of this software.
20: * Neither the name of the University nor the names of its contributors may
21: * be used to endorse or promote products derived from this software without
22: * specific prior written permission.
23: * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
24: * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
25: * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
26: */
27:
28: #ifndef lint
29: char copyright[] =
30: "@(#) Copyright (c) 1989 The Regents of the University of California.\n\
31: All rights reserved.\n";
32: #endif /* not lint */
33:
34: #ifndef lint
35: static char sccsid[] = "@(#)caesar.c 5.4 (Berkeley) 6/1/90";
36: #endif /* not lint */
37:
38: #include <math.h>
39: #include <stdio.h>
40: #include <ctype.h>
41: #include <unistd.h>
42:
43: #define LINELENGTH 2048
44: #define ROTATE(ch, perm) \
45: isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
46: islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch
47:
48: /*
49: * letter frequencies (taken from some unix(tm) documentation)
50: * (unix is a trademark of Bell Laboratories)
51: */
52: double stdf[26] = {
53: 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
54: 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
55: 2.62, 0.81, 1.88, 0.23, 2.07, 0.06,
56: };
57:
58: main(argc, argv)
59: int argc;
60: char **argv;
61: {
62: extern int errno;
63: register int ch, dot, i, nread, winnerdot;
64: register char *inbuf;
65: int obs[26], try, winner;
66: char *malloc(), *strerror();
67:
68: if (argc > 1)
69: printit(argv[1]);
70:
71: if (!(inbuf = malloc(LINELENGTH))) {
72: (void)fprintf(stderr, "caesar: out of memory.\n");
73: exit(1);
74: }
75:
76: /* adjust frequency table to weight low probs REAL low */
77: for (i = 0; i < 26; ++i)
78: stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
79:
80: /* zero out observation table */
81: bzero(obs, 26 * sizeof(int));
82:
83: if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) {
84: (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
85: exit(1);
86: }
87: for (i = nread; i--;) {
88: ch = inbuf[i];
89: if (islower(ch))
90: ++obs[ch - 'a'];
91: else if (isupper(ch))
92: ++obs[ch - 'A'];
93: }
94:
95: /*
96: * now "dot" the freqs with the observed letter freqs
97: * and keep track of best fit
98: */
99: for (try = winner = 0; try < 26; ++try) { /* += 13) { */
100: dot = 0;
101: for (i = 0; i < 26; i++)
102: dot += obs[i] * stdf[(i + try) % 26];
103: /* initialize winning score */
104: if (try == 0)
105: winnerdot = dot;
106: if (dot > winnerdot) {
107: /* got a new winner! */
108: winner = try;
109: winnerdot = dot;
110: }
111: }
112:
113: for (;;) {
114: for (i = 0; i < nread; ++i) {
115: ch = inbuf[i];
116: putchar(ROTATE(ch, winner));
117: }
118: if (nread < LINELENGTH)
119: break;
120: if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) {
121: (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
122: exit(1);
123: }
124: }
125: exit(0);
126: }
127:
128: printit(arg)
129: char *arg;
130: {
131: register int ch, rot;
132:
133: if ((rot = atoi(arg)) < 0) {
134: (void)fprintf(stderr, "caesar: bad rotation value.\n");
135: exit(1);
136: }
137: while ((ch = getchar()) != EOF)
138: putchar(ROTATE(ch, rot));
139: exit(0);
140: }
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