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/* $OpenBSD: caesar.c,v 1.19 2016/02/26 12:10:49 mestre Exp $ */
/*
* Copyright (c) 1989, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Rick Adams.
*
* Authors:
* Stan King, John Eldridge, based on algorithm suggested by
* Bob Morris
* 29-Sep-82
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#define LINELENGTH 2048
#define ROTATE(ch, perm) \
isupper(ch) ? ('A' + (ch - 'A' + perm) % 26) : \
islower(ch) ? ('a' + (ch - 'a' + perm) % 26) : ch
/*
* letter frequencies (taken from some unix(tm) documentation)
* (unix is a trademark of Bell Laboratories)
*/
double stdf[26] = {
7.97, 1.35, 3.61, 4.78, 12.37, 2.01, 1.46, 4.49, 6.39, 0.04,
0.42, 3.81, 2.69, 5.92, 6.96, 2.91, 0.08, 6.63, 8.77, 9.68,
2.62, 0.81, 1.88, 0.23, 2.07, 0.06
};
__dead void printit(int);
int
main(int argc, char *argv[])
{
int ch, i, nread;
extern char *__progname;
const char *errstr;
char *inbuf;
int obs[26], try, winner;
double dot, winnerdot;
if (pledge("stdio", NULL) == -1)
err(1, "pledge");
/* check to see if we were called as rot13 */
if (strcmp(__progname, "rot13") == 0)
printit(13);
if (argc > 1) {
i = strtonum(argv[1], 0, 25, &errstr);
if (errstr)
errx(1, "rotation is %s: %s", errstr, argv[1]);
else
printit(i);
}
if (!(inbuf = malloc(LINELENGTH)))
err(1, NULL);
/* adjust frequency table to weight low probs REAL low */
for (i = 0; i < 26; ++i)
stdf[i] = log(stdf[i]) + log(26.0 / 100.0);
/* zero out observation table */
memset(obs, 0, 26 * sizeof(int));
nread = 0;
while ((nread < LINELENGTH) && ((ch = getchar()) != EOF)) {
inbuf[nread++] = ch;
if (islower(ch))
++obs[ch - 'a'];
else if (isupper(ch))
++obs[ch - 'A'];
}
/*
* now "dot" the freqs with the observed letter freqs
* and keep track of best fit
*/
winnerdot = 0;
for (try = winner = 0; try < 26; ++try) { /* += 13) { */
dot = 0;
for (i = 0; i < 26; i++)
dot += obs[i] * stdf[(i + try) % 26];
if (dot > winnerdot) {
/* got a new winner! */
winner = try;
winnerdot = dot;
}
}
/* dump the buffer before calling printit */
for (i = 0; i < nread; ++i) {
ch = inbuf[i];
putchar(ROTATE(ch, winner));
}
printit(winner);
}
void
printit(int rot)
{
int ch;
while ((ch = getchar()) != EOF)
putchar(ROTATE(ch, rot));
exit(0);
}
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