mirror of
https://github.com/sheumann/hush.git
synced 2024-12-28 22:30:05 +00:00
76ace254e1
function old new delta next_random 46 68 +22 forkshell 248 263 +15 expand_vars_to_list 2118 2131 +13 run_pipe 1775 1782 +7 popstring 134 140 +6 builtin_umask 123 121 -2 ash_main 1356 1336 -20 get_local_var_value 125 104 -21 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 5/3 up/down: 63/-43) Total: 20 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
45 lines
1.2 KiB
C
45 lines
1.2 KiB
C
/* vi: set sw=4 ts=4: */
|
|
/*
|
|
* $RANDOM support.
|
|
*
|
|
* Copyright (C) 2009 Denys Vlasenko
|
|
*
|
|
* Licensed under GPLv2, see file LICENSE in this tarball for details.
|
|
*/
|
|
#include "libbb.h"
|
|
#include "random.h"
|
|
|
|
uint32_t FAST_FUNC
|
|
next_random(random_t *rnd)
|
|
{
|
|
/* Galois LFSR parameter */
|
|
/* Taps at 32 31 29 1: */
|
|
enum { MASK = 0x8000000b };
|
|
/* Another example - taps at 32 31 30 10: */
|
|
/* MASK = 0x00400007 */
|
|
|
|
uint32_t t;
|
|
|
|
if (UNINITED_RANDOM_T(rnd)) {
|
|
/* Can use monotonic_ns() for better randomness but for now
|
|
* it is not used anywhere else in busybox... so avoid bloat
|
|
*/
|
|
INIT_RANDOM_T(rnd, getpid(), monotonic_us());
|
|
}
|
|
|
|
/* LCG has period of 2^32 and alternating lowest bit */
|
|
rnd->LCG = 1664525 * rnd->LCG + 1013904223;
|
|
/* Galois LFSR has period of 2^32-1 = 3 * 5 * 17 * 257 * 65537 */
|
|
t = (rnd->galois_LFSR << 1);
|
|
if (rnd->galois_LFSR < 0) /* if we just shifted 1 out of msb... */
|
|
t ^= MASK;
|
|
rnd->galois_LFSR = t;
|
|
/* Both are weak, combining them gives better randomness
|
|
* and ~2^64 period. & 0x7fff is probably bash compat
|
|
* for $RANDOM range. Combining with subtraction is
|
|
* just for fun. + and ^ would work equally well. */
|
|
t = (t - rnd->LCG) & 0x7fff;
|
|
|
|
return t;
|
|
}
|