forked from tytso/pwgen
-
Notifications
You must be signed in to change notification settings - Fork 0
/
randnum.c
70 lines (61 loc) · 1.29 KB
/
randnum.c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
/*
* randnum.c -- generate (good) randum numbers.
*
* Copyright (C) 2001,2002 by Theodore Ts'o
*
* This file may be distributed under the terms of the GNU Public
* License.
*/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include "pwgen.h"
static int get_random_fd(void);
static int get_random_fd()
{
static int fd = -2;
if (fd == -2) {
fd = open("/dev/urandom", O_RDONLY);
if (fd == -1)
fd = open("/dev/random", O_RDONLY | O_NONBLOCK);
}
return fd;
}
/*
* Generate a random number n, where 0 <= n < max_num, using
* /dev/urandom if possible.
*/
int pw_random_number(max_num)
int max_num;
{
unsigned int rand_num;
int i, fd = get_random_fd();
int lose_counter = 0, nbytes = sizeof(rand_num);
char *cp = (char *) &rand_num;
if (fd >= 0) {
while (nbytes > 0) {
i = read(fd, cp, nbytes);
if ((i < 0) &&
((errno == EINTR) || (errno == EAGAIN)))
continue;
if (i <= 0) {
if (lose_counter++ == 8)
break;
continue;
}
nbytes -= i;
cp += i;
lose_counter = 0;
}
}
if (nbytes == 0)
return (rand_num % max_num);
/* We weren't able to use /dev/random, fail hard */
fprintf(stderr, "No entropy available!\n");
exit(1);
}