caesar/caesar.c

   1 /*      $NetBSD: caesar.c,v 1.3 1995/03/21 15:08:21 cgd 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. All advertising materials mentioning features or use of this software
  24  *    must display the following acknowledgement:
  25  *      This product includes software developed by the University of
  26  *      California, Berkeley and its contributors.
  27  * 4. Neither the name of the University nor the names of its contributors
  28  *    may be used to endorse or promote products derived from this software
  29  *    without specific prior written permission.
  30  *
  31  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  32  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  33  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  34  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  35  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  36  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  37  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  38  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  39  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  40  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  41  * SUCH DAMAGE.
  42  */
  43
  44 #ifndef lint
  45 static char copyright[] =
  46 "@(#) Copyright (c) 1989, 1993\n\
  47         The Regents of the University of California.  All rights reserved.\n";
  48 #endif /* not lint */
  49
  50 #ifndef lint
  51 #if 0
  52 static char sccsid[] = "@(#)caesar.c    8.1 (Berkeley) 5/31/93";
  53 #else
  54 static char rcsid[] = "$NetBSD: caesar.c,v 1.3 1995/03/21 15:08:21 cgd Exp $";
  55 #endif
  56 #endif /* not lint */
  57
  58 #include <math.h>
  59 #include <stdio.h>
  60 #include <ctype.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 main(argc, argv)
  79         int argc;
  80         char **argv;
  81 {
  82         extern int errno;
  83         register int ch, dot, i, nread, winnerdot;
  84         register char *inbuf;
  85         int obs[26], try, winner;
  86         char *malloc(), *strerror();
  87
  88         if (argc > 1)
  89                 printit(argv[1]);
  90
  91         if (!(inbuf = malloc(LINELENGTH))) {
  92                 (void)fprintf(stderr, "caesar: out of memory.\n");
  93                 exit(1);
  94         }
  95
  96         /* adjust frequency table to weight low probs REAL low */
  97         for (i = 0; i < 26; ++i)
  98                 stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
  99
 100         /* zero out observation table */
 101         bzero(obs, 26 * sizeof(int));
 102
 103         if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) {
 104                 (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
 105                 exit(1);
 106         }
 107         for (i = nread; i--;) {
 108                 ch = inbuf[i];
 109                 if (islower(ch))
 110                         ++obs[ch - 'a'];
 111                 else if (isupper(ch))
 112                         ++obs[ch - 'A'];
 113         }
 114
 115         /*
 116          * now "dot" the freqs with the observed letter freqs
 117          * and keep track of best fit
 118          */
 119         for (try = winner = 0; try < 26; ++try) { /* += 13) { */
 120                 dot = 0;
 121                 for (i = 0; i < 26; i++)
 122                         dot += obs[i] * stdf[(i + try) % 26];
 123                 /* initialize winning score */
 124                 if (try == 0)
 125                         winnerdot = dot;
 126                 if (dot > winnerdot) {
 127                         /* got a new winner! */
 128                         winner = try;
 129                         winnerdot = dot;
 130                 }
 131         }
 132
 133         for (;;) {
 134                 for (i = 0; i < nread; ++i) {
 135                         ch = inbuf[i];
 136                         putchar(ROTATE(ch, winner));
 137                 }
 138                 if (nread < LINELENGTH)
 139                         break;
 140                 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) {
 141                         (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
 142                         exit(1);
 143                 }
 144         }
 145         exit(0);
 146 }
 147
 148 printit(arg)
 149         char *arg;
 150 {
 151         register int ch, rot;
 152
 153         if ((rot = atoi(arg)) < 0) {
 154                 (void)fprintf(stderr, "caesar: bad rotation value.\n");
 155                 exit(1);
 156         }
 157         while ((ch = getchar()) != EOF)
 158                 putchar(ROTATE(ch, rot));
 159         exit(0);
 160 }