161 lines
4.6 KiB
C
161 lines
4.6 KiB
C
/*
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* Copyright (c) 1989, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Rick Adams.
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*
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* Authors:
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* Stan King, John Eldridge, based on algorithm suggested by
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* Bob Morris
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* 29-Sep-82
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#ifndef lint
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static const char copyright[] =
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"@(#) Copyright (c) 1989, 1993\n\
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The Regents of the University of California. All rights reserved.\n";
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#endif /* not lint */
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#ifndef lint
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static const char sccsid[] = "@(#)caesar.c 8.1 (Berkeley) 5/31/93";
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#endif /* not lint */
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#include <errno.h>
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#include <math.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <ctype.h>
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#include <unistd.h>
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#define LINELENGTH 2048
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#define ROTATE(ch, perm) \
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isascii(ch) ? ( \
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isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
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islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch) : ch
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/*
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* letter frequencies (taken from some unix(tm) documentation)
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* (unix is a trademark of Bell Laboratories)
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*/
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double stdf[26] = {
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7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
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0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
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2.62, 0.81, 1.88, 0.23, 2.07, 0.06,
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};
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void printit();
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void main(argc, argv)
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int argc;
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char **argv;
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{
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register int ch, dot, i, nread, winnerdot = 0;
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register char *inbuf;
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int obs[26], try, winner;
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if (argc > 1)
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printit(argv[1]);
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if (!(inbuf = malloc(LINELENGTH))) {
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(void)fprintf(stderr, "caesar: out of memory.\n");
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exit(1);
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}
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/* adjust frequency table to weight low probs REAL low */
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for (i = 0; i < 26; ++i)
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stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
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/* zero out observation table */
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bzero(obs, 26 * sizeof(int));
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if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) {
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(void)fprintf(stderr, "caesar: %s\n", strerror(errno));
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exit(1);
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}
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for (i = nread; i--;) {
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ch = (unsigned char) inbuf[i];
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if (isascii(ch)) {
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if (islower(ch))
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++obs[ch - 'a'];
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else if (isupper(ch))
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++obs[ch - 'A'];
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}
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}
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/*
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* now "dot" the freqs with the observed letter freqs
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* and keep track of best fit
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*/
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for (try = winner = 0; try < 26; ++try) { /* += 13) { */
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dot = 0;
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for (i = 0; i < 26; i++)
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dot += obs[i] * stdf[(i + try) % 26];
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/* initialize winning score */
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if (try == 0)
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winnerdot = dot;
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if (dot > winnerdot) {
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/* got a new winner! */
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winner = try;
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winnerdot = dot;
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}
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}
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for (;;) {
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for (i = 0; i < nread; ++i) {
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ch = (unsigned char) inbuf[i];
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putchar(ROTATE(ch, winner));
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}
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if (nread < LINELENGTH)
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break;
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if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) {
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(void)fprintf(stderr, "caesar: %s\n", strerror(errno));
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exit(1);
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}
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}
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exit(0);
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}
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void printit(arg)
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char *arg;
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{
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register int ch, rot;
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if ((rot = atoi(arg)) < 0) {
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(void)fprintf(stderr, "caesar: bad rotation value.\n");
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exit(1);
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}
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while ((ch = getchar()) != EOF)
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putchar(ROTATE(ch, rot));
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exit(0);
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}
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