games/caesar/caesar.c

   1 /*-
   2  * Copyright (c) 1989, 1993
   3  *      The Regents of the University of California.  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. Neither the name of the University nor the names of its contributors
  22  *    may be used to endorse or promote products derived from this software
  23  *    without specific prior written permission.
  24  *
  25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  35  * SUCH DAMAGE.
  36  *
  37  * $FreeBSD: src/games/caesar/caesar.c,v 1.8.2.1 2000/08/17 06:13:06 jhb Exp $
  38  * $DragonFly: src/games/caesar/caesar.c,v 1.4 2005/03/01 22:47:10 joerg Exp $
  39  *
  40  * @(#) Copyright (c) 1989, 1993 The Regents of the University of California.  All rights reserved.
  41  * @(#)caesar.c    8.1 (Berkeley) 5/31/93
  42  * $FreeBSD: src/games/caesar/caesar.c,v 1.8.2.1 2000/08/17 06:13:06 jhb Exp $
  43  */
  44
  45 #include <ctype.h>
  46 #include <err.h>
  47 #include <errno.h>
  48 #include <math.h>
  49 #include <stdio.h>
  50 #include <stdlib.h>
  51 #include <string.h>
  52 #include <unistd.h>
  53
  54 #define LETTERS         26
  55 #define LINELENGTH      2048
  56 #define ROTATE(ch, perm) \
  57      isascii(ch) ? ( \
  58         isupper(ch) ? ('A' + (ch - 'A' + perm) % LETTERS) : \
  59             islower(ch) ? ('a' + (ch - 'a' + perm) % LETTERS) : ch) : ch
  60
  61 /*
  62  * letter frequencies (taken from some unix(tm) documentation)
  63  * (unix is a trademark of Bell Laboratories)
  64  */
  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 void
  72 printit(const char *arg)
  73 {
  74         int ch, rot;
  75
  76         if ((rot = atoi(arg)) < 0)
  77                 errx(1, "bad rotation value");
  78
  79         while ((ch = getchar()) != EOF)
  80                 putchar(ROTATE(ch, rot));
  81         exit(0);
  82 }
  83
  84 int
  85 main(int argc, char *argv[])
  86 {
  87         int ch, dot, i, nread, winnerdot;
  88         char *inbuf;
  89         int obs[LETTERS], try, winner;
  90
  91         /* revoke setgid privileges */
  92         setgid(getgid());
  93
  94         if (argc > 1)
  95                 printit(argv[1]);
  96
  97         if ((inbuf = malloc(LINELENGTH)) == NULL)
  98                 err(1, "malloc failed");
  99
 100         /* adjust frequency table to weight low probs REAL low */
 101         for (i = 0; i < LETTERS; i++)
 102                 stdf[i] = log(stdf[i]) + log(LETTERS / 100.0);
 103
 104         /* zero out observation table */
 105         bzero(obs, LETTERS * sizeof(int));
 106
 107         if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
 108                 err(1, "read failed");
 109         for (i = nread; i--;) {
 110                 ch = (unsigned char) inbuf[i];
 111                 if (isascii(ch)) {
 112                         if (islower(ch))
 113                                 ++obs[ch - 'a'];
 114                         else if (isupper(ch))
 115                                 ++obs[ch - 'A'];
 116                 }
 117         }
 118
 119         /*
 120          * now "dot" the freqs with the observed letter freqs
 121          * and keep track of best fit
 122          */
 123         winner = 0;
 124         winnerdot = 0;
 125         for (try = 0; try < LETTERS; try++) {
 126                 dot = 0;
 127                 for (i = 0; i < LETTERS; i++)
 128                         dot += obs[i] * stdf[(i + try) % LETTERS];
 129                 /* initialize winning score */
 130                 if (try == 0)
 131                         winnerdot = dot;
 132                 if (dot > winnerdot) {
 133                         /* got a new winner! */
 134                         winner = try;
 135                         winnerdot = dot;
 136                 }
 137         }
 138
 139         for (;;) {
 140                 for (i = 0; i < nread; ++i) {
 141                         ch = (unsigned char) inbuf[i];
 142                         putchar(ROTATE(ch, winner));
 143                 }
 144                 if (nread < LINELENGTH)
 145                         break;
 146                 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
 147                         err(1, "read failed");
 148         }
 149         exit(0);
 150 }