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. All advertising materials mentioning features or use of this software
  22  *    must display the following acknowledgement:
  23  *      This product includes software developed by the University of
  24  *      California, Berkeley and its contributors.
  25  * 4. Neither the name of the University nor the names of its contributors
  26  *    may be used to endorse or promote products derived from this software
  27  *    without specific prior written permission.
  28  *
  29  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  30  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  31  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  32  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  33  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  34  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  35  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  36  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  37  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  38  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  39  * SUCH DAMAGE.
  40  *
  41  * $FreeBSD: src/games/caesar/caesar.c,v 1.8.2.1 2000/08/17 06:13:06 jhb Exp $
  42  * $DragonFly: src/games/caesar/caesar.c,v 1.4 2005/03/01 22:47:10 joerg Exp $
  43  *
  44  * @(#) Copyright (c) 1989, 1993 The Regents of the University of California.  All rights reserved.
  45  * @(#)caesar.c    8.1 (Berkeley) 5/31/93
  46  * $FreeBSD: src/games/caesar/caesar.c,v 1.8.2.1 2000/08/17 06:13:06 jhb Exp $
  47  */
  48
  49 #include <ctype.h>
  50 #include <err.h>
  51 #include <errno.h>
  52 #include <math.h>
  53 #include <stdio.h>
  54 #include <stdlib.h>
  55 #include <string.h>
  56 #include <unistd.h>
  57
  58 #define LINELENGTH      2048
  59 #define ROTATE(ch, perm) \
  60      isascii(ch) ? ( \
  61         isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
  62             islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch
  63
  64 /*
  65  * letter frequencies (taken from some unix(tm) documentation)
  66  * (unix is a trademark of Bell Laboratories)
  67  */
  68 static double stdf[26] = {
  69         7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
  70         0.42, 3.81, 2.69, 5.92,  6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
  71         2.62, 0.81, 1.88, 0.23,  2.07, 0.06,
  72 };
  73
  74 static void     printit(const char *);
  75
  76 int
  77 main(int argc, char **argv)
  78 {
  79         int ch, dot, i, nread, winnerdot = 0;
  80         char *inbuf;
  81         int obs[26], try, winner;
  82
  83         /* revoke setgid privileges */
  84         setgid(getgid());
  85
  86         if (argc > 1)
  87                 printit(argv[1]);
  88
  89         if ((inbuf = malloc(LINELENGTH)) == NULL)
  90                 err(1, "malloc failed");
  91
  92         /* adjust frequency table to weight low probs REAL low */
  93         for (i = 0; i < 26; ++i)
  94                 stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
  95
  96         /* zero out observation table */
  97         bzero(obs, 26 * sizeof(int));
  98
  99         if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
 100                 err(1, "read failed");
 101         for (i = nread; i--;) {
 102                 ch = (unsigned char) inbuf[i];
 103                 if (isascii(ch)) {
 104                         if (islower(ch))
 105                                 ++obs[ch - 'a'];
 106                         else if (isupper(ch))
 107                                 ++obs[ch - 'A'];
 108                 }
 109         }
 110
 111         /*
 112          * now "dot" the freqs with the observed letter freqs
 113          * and keep track of best fit
 114          */
 115         for (try = winner = 0; try < 26; ++try) { /* += 13) { */
 116                 dot = 0;
 117                 for (i = 0; i < 26; i++)
 118                         dot += obs[i] * stdf[(i + try) % 26];
 119                 /* initialize winning score */
 120                 if (try == 0)
 121                         winnerdot = dot;
 122                 if (dot > winnerdot) {
 123                         /* got a new winner! */
 124                         winner = try;
 125                         winnerdot = dot;
 126                 }
 127         }
 128
 129         for (;;) {
 130                 for (i = 0; i < nread; ++i) {
 131                         ch = (unsigned char) inbuf[i];
 132                         putchar(ROTATE(ch, winner));
 133                 }
 134                 if (nread < LINELENGTH)
 135                         break;
 136                 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
 137                         err(1, "read failed");
 138         }
 139         exit(0);
 140 }
 141
 142 static void
 143 printit(const char *arg)
 144 {
 145         int ch, rot;
 146
 147         if ((rot = atoi(arg)) < 0)
 148                 errx(1, "bad rotation value");
 149
 150         while ((ch = getchar()) != EOF)
 151                 putchar(ROTATE(ch, rot));
 152         exit(0);
 153 }