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989956f7 | 1 | /* |
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2 | * Copyright (c) 1989 The Regents of the University of California. |
3 | * All rights reserved. | |
989956f7 | 4 | * |
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5 | * This code is derived from software contributed to Berkeley by |
6 | * Rick Adams. | |
989956f7 | 7 | * |
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8 | * Authors: |
9 | * Stan King, John Eldridge, based on algorithm suggested by | |
10 | * Bob Morris | |
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11 | * 29-Sep-82 |
12 | * | |
a6547b1d | 13 | * %sccs.include.redist.c% |
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14 | */ |
15 | ||
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16 | #ifndef lint |
17 | char copyright[] = | |
18 | "@(#) Copyright (c) 1989 The Regents of the University of California.\n\ | |
19 | All rights reserved.\n"; | |
20 | #endif /* not lint */ | |
21 | ||
22 | #ifndef lint | |
a6547b1d | 23 | static char sccsid[] = "@(#)caesar.c 5.4 (Berkeley) %G%"; |
fd9714d7 | 24 | #endif /* not lint */ |
989956f7 | 25 | |
fd9714d7 | 26 | #include <math.h> |
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27 | #include <stdio.h> |
28 | #include <ctype.h> | |
7b8a3929 | 29 | #include <unistd.h> |
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30 | |
31 | #define LINELENGTH 2048 | |
32 | #define ROTATE(ch, perm) \ | |
7b8a3929 | 33 | isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \ |
fd9714d7 | 34 | islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch |
989956f7 | 35 | |
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36 | /* |
37 | * letter frequencies (taken from some unix(tm) documentation) | |
38 | * (unix is a trademark of Bell Laboratories) | |
39 | */ | |
40 | double stdf[26] = { | |
41 | 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, | |
42 | 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, | |
43 | 2.62, 0.81, 1.88, 0.23, 2.07, 0.06, | |
44 | }; | |
45 | ||
989956f7 | 46 | main(argc, argv) |
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47 | int argc; |
48 | char **argv; | |
989956f7 | 49 | { |
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50 | extern int errno; |
51 | register int ch, dot, i, nread, winnerdot; | |
fd9714d7 | 52 | register char *inbuf; |
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53 | int obs[26], try, winner; |
54 | char *malloc(), *strerror(); | |
989956f7 | 55 | |
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56 | if (argc > 1) |
57 | printit(argv[1]); | |
989956f7 | 58 | |
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59 | if (!(inbuf = malloc(LINELENGTH))) { |
60 | (void)fprintf(stderr, "caesar: out of memory.\n"); | |
61 | exit(1); | |
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62 | } |
63 | ||
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64 | /* adjust frequency table to weight low probs REAL low */ |
65 | for (i = 0; i < 26; ++i) | |
66 | stdf[i] = log(stdf[i]) + log(26.0 / 100.0); | |
67 | ||
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68 | /* zero out observation table */ |
69 | bzero(obs, 26 * sizeof(int)); | |
989956f7 | 70 | |
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71 | if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { |
72 | (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); | |
73 | exit(1); | |
74 | } | |
75 | for (i = nread; i--;) { | |
76 | ch = inbuf[i]; | |
77 | if (islower(ch)) | |
78 | ++obs[ch - 'a']; | |
79 | else if (isupper(ch)) | |
80 | ++obs[ch - 'A']; | |
81 | } | |
989956f7 | 82 | |
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83 | /* |
84 | * now "dot" the freqs with the observed letter freqs | |
85 | * and keep track of best fit | |
86 | */ | |
87 | for (try = winner = 0; try < 26; ++try) { /* += 13) { */ | |
88 | dot = 0; | |
89 | for (i = 0; i < 26; i++) | |
90 | dot += obs[i] * stdf[(i + try) % 26]; | |
91 | /* initialize winning score */ | |
92 | if (try == 0) | |
93 | winnerdot = dot; | |
94 | if (dot > winnerdot) { | |
95 | /* got a new winner! */ | |
96 | winner = try; | |
97 | winnerdot = dot; | |
989956f7 | 98 | } |
7b8a3929 | 99 | } |
989956f7 | 100 | |
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101 | for (;;) { |
102 | for (i = 0; i < nread; ++i) { | |
103 | ch = inbuf[i]; | |
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104 | putchar(ROTATE(ch, winner)); |
105 | } | |
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106 | if (nread < LINELENGTH) |
107 | break; | |
108 | if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) { | |
109 | (void)fprintf(stderr, "caesar: %s\n", strerror(errno)); | |
110 | exit(1); | |
111 | } | |
989956f7 | 112 | } |
7b8a3929 | 113 | exit(0); |
fd9714d7 | 114 | } |
989956f7 | 115 | |
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116 | printit(arg) |
117 | char *arg; | |
989956f7 | 118 | { |
7b8a3929 | 119 | register int ch, rot; |
fd9714d7 | 120 | |
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121 | if ((rot = atoi(arg)) < 0) { |
122 | (void)fprintf(stderr, "caesar: bad rotation value.\n"); | |
123 | exit(1); | |
124 | } | |
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125 | while ((ch = getchar()) != EOF) |
126 | putchar(ROTATE(ch, rot)); | |
7b8a3929 | 127 | exit(0); |
989956f7 | 128 | } |