Last change
on this file since 3586 was 2725, checked in by Bruno Cornec, 14 years ago |
- Update mindi-busybox to 1.18.3 to avoid problems with the tar command which is now failing on recent versions with busybox 1.7.3
|
-
Property svn:eol-style
set to
native
|
File size:
1.2 KB
|
Line | |
---|
1 | /* vi: set sw=4 ts=4: */
|
---|
2 | /*
|
---|
3 | * $RANDOM support.
|
---|
4 | *
|
---|
5 | * Copyright (C) 2009 Denys Vlasenko
|
---|
6 | *
|
---|
7 | * Licensed under GPLv2, see file LICENSE in this source tree.
|
---|
8 | */
|
---|
9 | #include "libbb.h"
|
---|
10 | #include "random.h"
|
---|
11 |
|
---|
12 | uint32_t FAST_FUNC
|
---|
13 | next_random(random_t *rnd)
|
---|
14 | {
|
---|
15 | /* Galois LFSR parameter */
|
---|
16 | /* Taps at 32 31 29 1: */
|
---|
17 | enum { MASK = 0x8000000b };
|
---|
18 | /* Another example - taps at 32 31 30 10: */
|
---|
19 | /* MASK = 0x00400007 */
|
---|
20 |
|
---|
21 | uint32_t t;
|
---|
22 |
|
---|
23 | if (UNINITED_RANDOM_T(rnd)) {
|
---|
24 | /* Can use monotonic_ns() for better randomness but for now
|
---|
25 | * it is not used anywhere else in busybox... so avoid bloat
|
---|
26 | */
|
---|
27 | INIT_RANDOM_T(rnd, getpid(), monotonic_us());
|
---|
28 | }
|
---|
29 |
|
---|
30 | /* LCG has period of 2^32 and alternating lowest bit */
|
---|
31 | rnd->LCG = 1664525 * rnd->LCG + 1013904223;
|
---|
32 | /* Galois LFSR has period of 2^32-1 = 3 * 5 * 17 * 257 * 65537 */
|
---|
33 | t = (rnd->galois_LFSR << 1);
|
---|
34 | if (rnd->galois_LFSR < 0) /* if we just shifted 1 out of msb... */
|
---|
35 | t ^= MASK;
|
---|
36 | rnd->galois_LFSR = t;
|
---|
37 | /* Both are weak, combining them gives better randomness
|
---|
38 | * and ~2^64 period. & 0x7fff is probably bash compat
|
---|
39 | * for $RANDOM range. Combining with subtraction is
|
---|
40 | * just for fun. + and ^ would work equally well. */
|
---|
41 | t = (t - rnd->LCG) & 0x7fff;
|
---|
42 |
|
---|
43 | return t;
|
---|
44 | }
|
---|
Note:
See
TracBrowser
for help on using the repository browser.