1/*	$NetBSD: random.c,v 1.16 2021/05/02 12:50:46 rillig Exp $	*/
2
3/*
4 * Copyright (c) 1994
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Guy Harris at Network Appliance Corp.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#include <sys/cdefs.h>
36#ifndef lint
37__COPYRIGHT("@(#) Copyright (c) 1994\
38 The Regents of the University of California.  All rights reserved.");
39#endif /* not lint */
40
41#ifndef lint
42#if 0
43static char sccsid[] = "@(#)random.c	8.6 (Berkeley) 6/1/94";
44#else
45__RCSID("$NetBSD: random.c,v 1.16 2021/05/02 12:50:46 rillig Exp $");
46#endif
47#endif /* not lint */
48
49#include <sys/types.h>
50#include <sys/time.h>
51
52#include <err.h>
53#include <errno.h>
54#include <stdio.h>
55#include <stdlib.h>
56#include <time.h>
57#include <unistd.h>
58#include <limits.h>
59
60static void usage(void) __dead;
61
62int
63main(int argc, char *argv[])
64{
65	double denom;
66	int ch, random_exit, selected, unbuffer_output;
67	char *ep;
68
69	denom = 0;
70	random_exit = unbuffer_output = 0;
71	while ((ch = getopt(argc, argv, "er")) != -1)
72		switch (ch) {
73		case 'e':
74			random_exit = 1;
75			break;
76		case 'r':
77			unbuffer_output = 1;
78			break;
79		default:
80		case '?':
81			usage();
82			/* NOTREACHED */
83		}
84
85	argc -= optind;
86	argv += optind;
87
88	switch (argc) {
89	case 0:
90		denom = 2;
91		break;
92	case 1:
93		errno = 0;
94		denom = strtod(*argv, &ep);
95		if (errno == ERANGE)
96			err(1, "%s", *argv);
97		if (denom == 0 || *ep != '\0')
98			errx(1, "denominator is not valid.");
99		break;
100	default:
101		usage();
102		/* NOTREACHED */
103	}
104
105	/* Compute a random exit status between 0 and denom - 1. */
106	if (random_exit)
107		return arc4random_uniform(denom);
108
109	/*
110	 * Act as a filter, randomly choosing lines of the standard input
111	 * to write to the standard output.
112	 */
113	if (unbuffer_output)
114		setbuf(stdout, NULL);
115
116	/*
117	 * Select whether to print the first line.  (Prime the pump.)
118	 * We find a random number between 0 and denom - 1 and, if it's
119	 * 0 (which has a 1 / denom chance of being true), we select the
120	 * line.
121	 */
122	selected = (arc4random_uniform(denom) == 0);
123	while ((ch = getchar()) != EOF) {
124		if (selected)
125			(void)putchar(ch);
126		if (ch == '\n') {
127			/* End of that line.  See if we got an error. */
128			if (ferror(stdout))
129				err(2, "stdout");
130
131			/* Now see if the next line is to be printed. */
132			selected = (arc4random_uniform(denom) == 0);
133		}
134	}
135	if (ferror(stdin))
136		err(2, "stdin");
137	exit (0);
138
139	return 0;
140}
141
142static void
143usage(void)
144{
145
146	(void)fprintf(stderr, "usage: random [-er] [denominator]\n");
147	exit(1);
148}
149