usr.bin/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
  38 #include <errno.h>
  39 #include <math.h>
  40 #include <stdio.h>
  41 #include <stdlib.h>
  42 #include <string.h>
  43 #include <ctype.h>
  44 #include <unistd.h>
  45
  46 #define LINELENGTH      2048
  47 #define ROTATE(ch, perm) \
  48      isascii(ch) ? ( \
  49         isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
  50             islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch
  51
  52 /*
  53  * letter frequencies (taken from some unix(tm) documentation)
  54  * (unix is a trademark of Bell Laboratories)
  55  */
  56 static double stdf[26] = {
  57         7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
  58         0.42, 3.81, 2.69, 5.92,  6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
  59         2.62, 0.81, 1.88, 0.23,  2.07, 0.06,
  60 };
  61
  62 static void printit(char *);
  63
  64 int
  65 main(int argc, char **argv)
  66 {
  67         int ch, dot, i, nread, winnerdot = 0;
  68         char *inbuf;
  69         int obs[26], try, winner;
  70
  71         if (argc > 1)
  72                 printit(argv[1]);
  73
  74         if (!(inbuf = malloc((size_t)LINELENGTH))) {
  75                 (void)fprintf(stderr, "caesar: out of memory.\n");
  76                 exit(1);
  77         }
  78
  79         /* adjust frequency table to weight low probs REAL low */
  80         for (i = 0; i < 26; ++i)
  81                 stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
  82
  83         /* zero out observation table */
  84         bzero(obs, 26 * sizeof(int));
  85
  86         if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) {
  87                 (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
  88                 exit(1);
  89         }
  90         for (i = nread; i--;) {
  91                 ch = (unsigned char) inbuf[i];
  92                 if (isascii(ch)) {
  93                         if (islower(ch))
  94                                 ++obs[ch - 'a'];
  95                         else if (isupper(ch))
  96                                 ++obs[ch - 'A'];
  97                 }
  98         }
  99
 100         /*
 101          * now "dot" the freqs with the observed letter freqs
 102          * and keep track of best fit
 103          */
 104         for (try = winner = 0; try < 26; ++try) { /* += 13) { */
 105                 dot = 0;
 106                 for (i = 0; i < 26; i++)
 107                         dot += obs[i] * stdf[(i + try) % 26];
 108                 /* initialize winning score */
 109                 if (try == 0)
 110                         winnerdot = dot;
 111                 if (dot > winnerdot) {
 112                         /* got a new winner! */
 113                         winner = try;
 114                         winnerdot = dot;
 115                 }
 116         }
 117
 118         for (;;) {
 119                 for (i = 0; i < nread; ++i) {
 120                         ch = (unsigned char) inbuf[i];
 121                         putchar(ROTATE(ch, winner));
 122                 }
 123                 if (nread < LINELENGTH)
 124                         break;
 125                 if ((nread = read(STDIN_FILENO, inbuf, (size_t)LINELENGTH)) < 0) {
 126                         (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
 127                         exit(1);
 128                 }
 129         }
 130         exit(0);
 131 }
 132
 133 static void
 134 printit(char *arg)
 135 {
 136         int ch, rot;
 137
 138         if ((rot = atoi(arg)) < 0) {
 139                 (void)fprintf(stderr, "caesar: bad rotation value.\n");
 140                 exit(1);
 141         }
 142         while ((ch = getchar()) != EOF)
 143                 putchar(ROTATE(ch, rot));
 144         exit(0);
 145 }