caesar.c revision 1.25
1 /* $NetBSD: caesar.c,v 1.25 2025/09/18 22:25:04 rillig Exp $ */ 2 3 /* 4 * Copyright (c) 1989, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This code is derived from software contributed to Berkeley by 8 * Rick Adams. 9 * 10 * Authors: 11 * Stan King, John Eldridge, based on algorithm suggested by 12 * Bob Morris 13 * 29-Sep-82 14 * Roland Illig, 2005, 2025 15 * 16 * Redistribution and use in source and binary forms, with or without 17 * modification, are permitted provided that the following conditions 18 * are met: 19 * 1. Redistributions of source code must retain the above copyright 20 * notice, this list of conditions and the following disclaimer. 21 * 2. Redistributions in binary form must reproduce the above copyright 22 * notice, this list of conditions and the following disclaimer in the 23 * documentation and/or other materials provided with the distribution. 24 * 3. Neither the name of the University nor the names of its contributors 25 * may be used to endorse or promote products derived from this software 26 * without specific prior written permission. 27 * 28 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 29 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 30 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 31 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 32 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 33 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 34 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 35 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 37 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 38 * SUCH DAMAGE. 39 */ 40 41 #include <sys/cdefs.h> 42 __COPYRIGHT("@(#) Copyright (c) 1989, 1993\ 43 The Regents of the University of California. All rights reserved."); 44 45 /* @(#)caesar.c 8.1 (Berkeley) 5/31/93 */ 46 __RCSID("$NetBSD: caesar.c,v 1.25 2025/09/18 22:25:04 rillig Exp $"); 47 48 #include <err.h> 49 #include <errno.h> 50 #include <limits.h> 51 #include <math.h> 52 #include <stdio.h> 53 #include <string.h> 54 #include <stdlib.h> 55 56 #define NCHARS (1 << CHAR_BIT) 57 #define LETTERS (26) 58 59 /* 60 * letter frequencies (taken from some unix(tm) documentation) 61 * (unix is a trademark of Bell Laboratories) 62 */ 63 static const unsigned char upper[LETTERS] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; 64 static const unsigned char lower[LETTERS] = "abcdefghijklmnopqrstuvwxyz"; 65 static double stdf[LETTERS] = { 66 7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04, 67 0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68, 68 2.62, 0.81, 1.88, 0.23, 2.07, 0.06 69 }; 70 71 static unsigned char rottbl[NCHARS]; 72 73 74 static void 75 init_rottbl(unsigned int rot) 76 { 77 78 rot %= LETTERS; /* prevent integer overflow */ 79 80 for (size_t i = 0; i < NCHARS; i++) 81 rottbl[i] = (unsigned char)i; 82 83 for (size_t i = 0; i < LETTERS; i++) 84 rottbl[upper[i]] = upper[(i + rot) % LETTERS]; 85 86 for (size_t i = 0; i < LETTERS; i++) 87 rottbl[lower[i]] = lower[(i + rot) % LETTERS]; 88 } 89 90 static void 91 print_file(void) 92 { 93 int ch; 94 95 while ((ch = getchar()) != EOF) 96 if (putchar(rottbl[ch]) == EOF) 97 err(EXIT_FAILURE, "<stdout>"); 98 } 99 100 static void 101 print_array(const unsigned char *a, size_t len) 102 { 103 104 for (size_t i = 0; i < len; i++) 105 if (putchar(rottbl[a[i]]) == EOF) 106 err(EXIT_FAILURE, "<stdout>"); 107 } 108 109 static unsigned int 110 get_rotation(const char *arg) 111 { 112 long rot; 113 char *endp; 114 115 errno = 0; 116 rot = strtol(arg, &endp, 10); 117 if (errno == 0 && (arg[0] == '\0' || *endp != '\0')) 118 errno = EINVAL; 119 if (errno == 0 && (rot < 0 || rot > INT_MAX)) 120 errno = ERANGE; 121 if (errno) 122 err(EXIT_FAILURE, "Bad rotation value `%s'", arg); 123 return (unsigned int)rot; 124 } 125 126 static void 127 guess_and_rotate(void) 128 { 129 unsigned char inbuf[2048]; 130 unsigned int obs[NCHARS]; 131 size_t i, nread; 132 double dot, winnerdot; 133 unsigned int try, winner; 134 int ch; 135 136 /* adjust frequency table to weight low probs REAL low */ 137 for (i = 0; i < LETTERS; i++) 138 stdf[i] = log(stdf[i]) + log(LETTERS / 100.0); 139 140 /* zero out observation table */ 141 (void)memset(obs, 0, sizeof(obs)); 142 143 for (nread = 0; nread < sizeof(inbuf); nread++) { 144 if ((ch = getchar()) == EOF) 145 break; 146 inbuf[nread] = (unsigned char)ch; 147 } 148 149 for (i = 0; i < nread; i++) 150 obs[inbuf[i]]++; 151 152 /* 153 * now "dot" the freqs with the observed letter freqs 154 * and keep track of best fit 155 */ 156 winner = 0; 157 winnerdot = 0.0; 158 for (try = 0; try < LETTERS; try++) { 159 dot = 0.0; 160 for (i = 0; i < LETTERS; i++) 161 dot += (obs[upper[i]] + obs[lower[i]]) 162 * stdf[(i + try) % LETTERS]; 163 164 if (try == 0 || dot > winnerdot) { 165 /* got a new winner! */ 166 winner = try; 167 winnerdot = dot; 168 } 169 } 170 171 init_rottbl(winner); 172 print_array(inbuf, nread); 173 print_file(); 174 } 175 176 int 177 main(int argc, char **argv) 178 { 179 180 if (argc == 1) 181 guess_and_rotate(); 182 else if (argc == 2) { 183 init_rottbl(get_rotation(argv[1])); 184 print_file(); 185 } else { 186 (void)fprintf(stderr, "usage: caesar [rotation]\n"); 187 exit(EXIT_FAILURE); 188 } 189 190 if (ferror(stdin) != 0) 191 errx(EXIT_FAILURE, "<stdin>: read error"); 192 193 (void)fflush(stdout); 194 if (ferror(stdout) != 0) 195 errx(EXIT_FAILURE, "<stdout>: write error"); 196 197 return 0; 198 } 199
Indexes created Wed Oct 01 07:09:59 GMT 2025