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22bad1fa WJ |
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, with or without | |
14 | * modification, are permitted provided that the following conditions | |
15 | * are met: | |
16 | * 1. Redistributions of source code must retain the above copyright | |
17 | * notice, this list of conditions and the following disclaimer. | |
18 | * 2. Redistributions in binary form must reproduce the above copyright | |
19 | * notice, this list of conditions and the following disclaimer in the | |
20 | * documentation and/or other materials provided with the distribution. | |
21 | * 3. All advertising materials mentioning features or use of this software | |
22 | * must display the following acknowledgement: | |
23 | * This product includes software developed by the University of | |
24 | * California, Berkeley and its contributors. | |
25 | * 4. Neither the name of the University nor the names of its contributors | |
26 | * may be used to endorse or promote products derived from this software | |
27 | * without specific prior written permission. | |
28 | * | |
29 | * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
30 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
31 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
32 | * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
33 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
34 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
35 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
36 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
37 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
38 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
39 | * SUCH DAMAGE. | |
40 | */ | |
41 | ||
42 | #ifndef lint | |
43 | char copyright[] = | |
44 | "@(#) Copyright (c) 1989 The Regents of the University of California.\n\ | |
45 | All rights reserved.\n"; | |
46 | #endif /* not lint */ | |
47 | ||
48 | #ifndef lint | |
49 | static char sccsid[] = "@(#)caesar.c 5.4 (Berkeley) 6/1/90"; | |
50 | #endif /* not lint */ | |
51 | ||
52 | #include <math.h> | |
53 | #include <stdio.h> | |
54 | #include <ctype.h> | |
55 | #include <unistd.h> | |
56 | ||
57 | #define LINELENGTH 2048 | |
58 | #define ROTATE(ch, perm) \ | |
59 | isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ | |
60 | islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch | |
61 | ||
62 | /* | |
63 | * letter frequencies (taken from some unix(tm) documentation) | |
64 | * (unix is a trademark of Bell Laboratories) | |
65 | */ | |
66 | double stdf[26] = { | |
67 | 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, | |
68 | 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, | |
69 | 2.62, 0.81, 1.88, 0.23, 2.07, 0.06, | |
70 | }; | |
71 | ||
72 | main(argc, argv) | |
73 | int argc; | |
74 | char **argv; | |
75 | { | |
76 | extern int errno; | |
77 | register int ch, dot, i, nread, winnerdot; | |
78 | register char *inbuf; | |
79 | int obs[26], try, winner; | |
80 | char *malloc(), *strerror(); | |
81 | ||
82 | if (argc > 1) | |
83 | printit(argv[1]); | |
84 | ||
85 | if (!(inbuf = malloc(LINELENGTH))) { | |
86 | (void)fprintf(stderr, "caesar: out of memory.\n"); | |
87 | exit(1); | |
88 | } | |
89 | ||
90 | /* adjust frequency table to weight low probs REAL low */ | |
91 | for (i = 0; i < 26; ++i) | |
92 | stdf[i] = log(stdf[i]) + log(26.0 / 100.0); | |
93 | ||
94 | /* zero out observation table */ | |
95 | bzero(obs, 26 * sizeof(int)); | |
96 | ||
97 | if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { | |
98 | (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); | |
99 | exit(1); | |
100 | } | |
101 | for (i = nread; i--;) { | |
102 | ch = inbuf[i]; | |
103 | if (islower(ch)) | |
104 | ++obs[ch - 'a']; | |
105 | else if (isupper(ch)) | |
106 | ++obs[ch - 'A']; | |
107 | } | |
108 | ||
109 | /* | |
110 | * now "dot" the freqs with the observed letter freqs | |
111 | * and keep track of best fit | |
112 | */ | |
113 | for (try = winner = 0; try < 26; ++try) { /* += 13) { */ | |
114 | dot = 0; | |
115 | for (i = 0; i < 26; i++) | |
116 | dot += obs[i] * stdf[(i + try) % 26]; | |
117 | /* initialize winning score */ | |
118 | if (try == 0) | |
119 | winnerdot = dot; | |
120 | if (dot > winnerdot) { | |
121 | /* got a new winner! */ | |
122 | winner = try; | |
123 | winnerdot = dot; | |
124 | } | |
125 | } | |
126 | ||
127 | for (;;) { | |
128 | for (i = 0; i < nread; ++i) { | |
129 | ch = inbuf[i]; | |
130 | putchar(ROTATE(ch, winner)); | |
131 | } | |
132 | if (nread < LINELENGTH) | |
133 | break; | |
134 | if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { | |
135 | (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); | |
136 | exit(1); | |
137 | } | |
138 | } | |
139 | exit(0); | |
140 | } | |
141 | ||
142 | printit(arg) | |
143 | char *arg; | |
144 | { | |
145 | register int ch, rot; | |
146 | ||
147 | if ((rot = atoi(arg)) < 0) { | |
148 | (void)fprintf(stderr, "caesar: bad rotation value.\n"); | |
149 | exit(1); | |
150 | } | |
151 | while ((ch = getchar()) != EOF) | |
152 | putchar(ROTATE(ch, rot)); | |
153 | exit(0); | |
154 | } |