BSD 4_3_Reno release

[unix-history] / usr / src / games / caesar / caesar.c

/*
* Copyright (c) 1989 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 are permitted provided
* that: (1) source distributions retain this entire copyright notice and
* comment, and (2) distributions including binaries display the following
* acknowledgement:  ``This product includes software developed by the
* University of California, Berkeley and its contributors'' in the
* documentation or other materials provided with the distribution and in
* all advertising materials mentioning features or use of this software.
* 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 ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*/

#ifndef lint
char copyright[] =
"@(#) Copyright (c) 1989 The Regents of the University of California.\n\
All rights reserved.\n";
#endif /* not lint */

#ifndef lint
static char sccsid[] = "@(#)caesar.c    5.4 (Berkeley) 6/1/90";
#endif /* not lint */

#include <math.h>
#include <stdio.h>
#include <ctype.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,
};

main(argc, argv)
       int argc;
       char **argv;
{
       extern int errno;
       register int ch, dot, i, nread, winnerdot;
       register char *inbuf;
       int obs[26], try, winner;
       char *malloc(), *strerror();

       if (argc > 1)
               printit(argv[1]);

       if (!(inbuf = malloc(LINELENGTH))) {
               (void)fprintf(stderr, "caesar: out of memory.\n");
               exit(1);
       }

       /* 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 */
       bzero(obs, 26 * sizeof(int));

       if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) {
               (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
               exit(1);
       }
       for (i = nread; i--;) {
               ch = inbuf[i];
               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
        */
       for (try = winner = 0; try < 26; ++try) { /* += 13) { */
               dot = 0;
               for (i = 0; i < 26; i++)
                       dot += obs[i] * stdf[(i + try) % 26];
               /* initialize winning score */
               if (try == 0)
                       winnerdot = dot;
               if (dot > winnerdot) {
                       /* got a new winner! */
                       winner = try;
                       winnerdot = dot;
               }
       }

       for (;;) {
               for (i = 0; i < nread; ++i) {
                       ch = inbuf[i];
                       putchar(ROTATE(ch, winner));
               }
               if (nread < LINELENGTH)
                       break;
               if ((nread = read(STDIN_FILENO, inbuf, LINELENGTH)) < 0) {
                       (void)fprintf(stderr, "caesar: %s\n", strerror(errno));
                       exit(1);
               }
       }
       exit(0);
}

printit(arg)
       char *arg;
{
       register int ch, rot;

       if ((rot = atoi(arg)) < 0) {
               (void)fprintf(stderr, "caesar: bad rotation value.\n");
               exit(1);
       }
       while ((ch = getchar()) != EOF)
               putchar(ROTATE(ch, rot));
       exit(0);
}