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  * @(#) Copyright (c) 1989, 1993 The Regents of the University of California.  All rights reserved.
  38  * @(#)caesar.c    8.1 (Berkeley) 5/31/93
  39  * $FreeBSD: head/usr.bin/caesar/caesar.c 241846 2012-10-22 03:06:53Z eadler $
  40  */
  41
  42 #include <ctype.h>
  43 #include <err.h>
  44 #include <errno.h>
  45 #include <math.h>
  46 #include <stdio.h>
  47 #include <stdlib.h>
  48 #include <string.h>
  49 #include <unistd.h>
  50
  51 #define LETTERS         26
  52 #define LINELENGTH      2048
  53 #define ROTATE(ch, perm) \
  54      isascii(ch) ? ( \
  55         isupper(ch) ? ('A' + (ch - 'A' + perm) % LETTERS) : \
  56             islower(ch) ? ('a' + (ch - 'a' + perm) % LETTERS) : ch) : ch
  57
  58 /*
  59  * letter frequencies (taken from some unix(tm) documentation)
  60  * (unix is a trademark of Bell Laboratories)
  61  */
  62 static double stdf[LETTERS] = {
  63         7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
  64         0.42, 3.81, 2.69, 5.92,  6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
  65         2.62, 0.81, 1.88, 0.23,  2.07, 0.06
  66 };
  67
  68 static void
  69 printit(const char *arg)
  70 {
  71         int ch, rot;
  72
  73         if ((rot = atoi(arg)) < 0)
  74                 errx(1, "bad rotation value");
  75
  76         while ((ch = getchar()) != EOF)
  77                 putchar(ROTATE(ch, rot));
  78         exit(0);
  79 }
  80
  81 int
  82 main(int argc, char *argv[])
  83 {
  84         int ch, dot, i, nread, winnerdot;
  85         char *inbuf;
  86         int obs[LETTERS], try, winner;
  87
  88         /* revoke setgid privileges */
  89         setgid(getgid());
  90
  91         if (argc > 1)
  92                 printit(argv[1]);
  93
  94         if ((inbuf = malloc(LINELENGTH)) == NULL)
  95                 err(1, "malloc failed");
  96
  97         /* adjust frequency table to weight low probs REAL low */
  98         for (i = 0; i < LETTERS; i++)
  99                 stdf[i] = log(stdf[i]) + log(LETTERS / 100.0);
 100
 101         /* zero out observation table */
 102         bzero(obs, LETTERS * sizeof(int));
 103
 104         if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
 105                 err(1, "read failed");
 106         for (i = nread; i--;) {
 107                 ch = (unsigned char) inbuf[i];
 108                 if (isascii(ch)) {
 109                         if (islower(ch))
 110                                 ++obs[ch - 'a'];
 111                         else if (isupper(ch))
 112                                 ++obs[ch - 'A'];
 113                 }
 114         }
 115
 116         /*
 117          * now "dot" the freqs with the observed letter freqs
 118          * and keep track of best fit
 119          */
 120         winner = 0;
 121         winnerdot = 0;
 122         for (try = 0; try < LETTERS; try++) {
 123                 dot = 0;
 124                 for (i = 0; i < LETTERS; i++)
 125                         dot += obs[i] * stdf[(i + try) % LETTERS];
 126                 /* initialize winning score */
 127                 if (try == 0)
 128                         winnerdot = dot;
 129                 if (dot > winnerdot) {
 130                         /* got a new winner! */
 131                         winner = try;
 132                         winnerdot = dot;
 133                 }
 134         }
 135
 136         for (;;) {
 137                 for (i = 0; i < nread; ++i) {
 138                         ch = (unsigned char) inbuf[i];
 139                         putchar(ROTATE(ch, winner));
 140                 }
 141                 if (nread < LINELENGTH)
 142                         break;
 143                 if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
 144                         err(1, "read failed");
 145         }
 146         exit(0);
 147 }