caesar/caesar.c

   1 /*      $NetBSD: caesar.c,v 1.14 2004/01/27 20:30:29 jsm 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  *
  15  * Redistribution and use in source and binary forms, with or without
  16  * modification, are permitted provided that the following conditions
  17  * are met:
  18  * 1. Redistributions of source code must retain the above copyright
  19  *    notice, this list of conditions and the following disclaimer.
  20  * 2. Redistributions in binary form must reproduce the above copyright
  21  *    notice, this list of conditions and the following disclaimer in the
  22  *    documentation and/or other materials provided with the distribution.
  23  * 3. Neither the name of the University nor the names of its contributors
  24  *    may be used to endorse or promote products derived from this software
  25  *    without specific prior written permission.
  26  *
  27  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  28  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  29  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  30  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  31  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  32  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  33  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  34  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  35  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  36  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  37  * SUCH DAMAGE.
  38  */
  39
  40 #include <sys/cdefs.h>
  41 #ifndef lint
  42 __COPYRIGHT("@(#) Copyright (c) 1989, 1993\n\
  43         The Regents of the University of California.  All rights reserved.\n");
  44 #endif /* not lint */
  45
  46 #ifndef lint
  47 #if 0
  48 static char sccsid[] = "@(#)caesar.c    8.1 (Berkeley) 5/31/93";
  49 #else
  50 __RCSID("$NetBSD: caesar.c,v 1.14 2004/01/27 20:30:29 jsm Exp $");
  51 #endif
  52 #endif /* not lint */
  53
  54 #include <ctype.h>
  55 #include <err.h>
  56 #include <errno.h>
  57 #include <math.h>
  58 #include <stdio.h>
  59 #include <string.h>
  60 #include <stdlib.h>
  61 #include <unistd.h>
  62
  63 #define LINELENGTH      2048
  64 #define ROTATE(ch, perm) \
  65         isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
  66             islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch
  67
  68 /*
  69  * letter frequencies (taken from some unix(tm) documentation)
  70  * (unix is a trademark of Bell Laboratories)
  71  */
  72 double stdf[26] = {
  73         7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
  74         0.42, 3.81, 2.69, 5.92,  6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
  75         2.62, 0.81, 1.88, 0.23,  2.07, 0.06,
  76 };
  77
  78
  79 int     main(int, char *[]);
  80 void    printit(const char *) __attribute__((__noreturn__));
  81
  82 int
  83 main(argc, argv)
  84         int argc;
  85         char **argv;
  86 {
  87         int ch, i, nread;
  88         double dot, winnerdot;
  89         char *inbuf;
  90         int obs[26], try, winner;
  91
  92         /* revoke setgid privileges */
  93         setgid(getgid());
  94
  95         winnerdot = 0;
  96         if (argc > 1)
  97                 printit(argv[1]);
  98
  99         if (!(inbuf = malloc(LINELENGTH)))
 100                 err(1, NULL);
 101
 102         /* adjust frequency table to weight low probs REAL low */
 103         for (i = 0; i < 26; ++i)
 104                 stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
 105
 106         /* zero out observation table */
 107         memset(obs, 0, 26 * sizeof(int));
 108
 109         if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
 110                 err(1, "reading from stdin");
 111         for (i = nread; i--;) {
 112                 ch = inbuf[i];
 113                 if (islower(ch))
 114                         ++obs[ch - 'a'];
 115                 else if (isupper(ch))
 116                         ++obs[ch - 'A'];
 117         }
 118
 119         /*
 120          * now "dot" the freqs with the observed letter freqs
 121          * and keep track of best fit
 122          */
 123         for (try = winner = 0; try < 26; ++try) { /* += 13) { */
 124                 dot = 0;
 125                 for (i = 0; i < 26; i++)
 126                         dot += obs[i] * stdf[(i + try) % 26];
 127                 /* initialize winning score */
 128                 if (try == 0)
 129                         winnerdot = dot;
 130                 if (dot > winnerdot) {
 131                         /* got a new winner! */
 132                         winner = try;
 133                         winnerdot = dot;
 134                 }
 135         }
 136
 137         for (;;) {
 138                 for (i = 0; i < nread; ++i) {
 139                         ch = inbuf[i];
 140                         putchar(ROTATE(ch, winner));
 141                 }
 142                 if (nread < LINELENGTH)
 143                         break;
 144                 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
 145                         err(1, "reading from stdin");
 146         }
 147         exit(0);
 148 }
 149
 150 void
 151 printit(arg)
 152         const char *arg;
 153 {
 154         int ch, rot;
 155
 156         if ((rot = atoi(arg)) < 0)
 157                 errx(1, "bad rotation value.");
 158         while ((ch = getchar()) != EOF)
 159                 putchar(ROTATE(ch, rot));
 160         exit(0);
 161 }