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caesar.c revision 1.6 
      1 /*	$NetBSD: caesar.c,v 1.6 1997/10/11 02:40:39 lukem 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 #include <sys/cdefs.h>
     45 #ifndef lint
     46 __COPYRIGHT("@(#) 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 __RCSID("$NetBSD: caesar.c,v 1.6 1997/10/11 02:40:39 lukem Exp $");
     55 #endif
     56 #endif /* not lint */
     57 
     58 #include <ctype.h>
     59 #include <err.h>
     60 #include <errno.h>
     61 #include <math.h>
     62 #include <stdio.h>
     63 #include <string.h>
     64 #include <stdlib.h>
     65 #include <unistd.h>
     66 
     67 #define	LINELENGTH	2048
     68 #define	ROTATE(ch, perm) \
     69 	isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
     70 	    islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch
     71 
     72 /*
     73  * letter frequencies (taken from some unix(tm) documentation)
     74  * (unix is a trademark of Bell Laboratories)
     75  */
     76 double stdf[26] = {
     77 	7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
     78 	0.42, 3.81, 2.69, 5.92,  6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
     79 	2.62, 0.81, 1.88, 0.23,  2.07, 0.06,
     80 };
     81 
     82 
     83 int	main __P((int, char *[]));
     84 void	printit __P((char *));
     85 
     86 int
     87 main(argc, argv)
     88 	int argc;
     89 	char **argv;
     90 {
     91 	int ch, dot, i, nread, winnerdot;
     92 	char *inbuf;
     93 	int obs[26], try, winner;
     94 
     95 	winnerdot = 0;
     96 	if (argc > 1)
     97 		printit(argv[1]);
     98 
     99 	if (!(inbuf = malloc(LINELENGTH)))
    100 		errx(1, "out of memory");
    101 
    102 	/* adjust frequency table to weight low probs REAL low */
    103 	for (i = 0; i < 26; ++i)
    104 		stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
    105 
    106 	/* zero out observation table */
    107 	memset(obs, 0, 26 * sizeof(int));
    108 
    109 	if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
    110 		err(1, "reading from stdin");
    111 	for (i = nread; i--;) {
    112 		ch = inbuf[i];
    113 		if (islower(ch))
    114 			++obs[ch - 'a'];
    115 		else if (isupper(ch))
    116 			++obs[ch - 'A'];
    117 	}
    118 
    119 	/*
    120 	 * now "dot" the freqs with the observed letter freqs
    121 	 * and keep track of best fit
    122 	 */
    123 	for (try = winner = 0; try < 26; ++try) { /* += 13) { */
    124 		dot = 0;
    125 		for (i = 0; i < 26; i++)
    126 			dot += obs[i] * stdf[(i + try) % 26];
    127 		/* initialize winning score */
    128 		if (try == 0)
    129 			winnerdot = dot;
    130 		if (dot > winnerdot) {
    131 			/* got a new winner! */
    132 			winner = try;
    133 			winnerdot = dot;
    134 		}
    135 	}
    136 
    137 	for (;;) {
    138 		for (i = 0; i < nread; ++i) {
    139 			ch = inbuf[i];
    140 			putchar(ROTATE(ch, winner));
    141 		}
    142 		if (nread < LINELENGTH)
    143 			break;
    144 		if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0)
    145 			err(1, "reading from stdin");
    146 	}
    147 	exit(0);
    148 }
    149 
    150 void
    151 printit(arg)
    152 	char *arg;
    153 {
    154 	int ch, rot;
    155 
    156 	if ((rot = atoi(arg)) < 0)
    157 		errx(1, "bad rotation value.");
    158 	while ((ch = getchar()) != EOF)
    159 		putchar(ROTATE(ch, rot));
    160 	exit(0);
    161 }
    162