diff options
| author | Matthew Dempsky <matthew@cvs.openbsd.org> | 2012-06-24 18:25:13 +0000 |
|---|---|---|
| committer | Matthew Dempsky <matthew@cvs.openbsd.org> | 2012-06-24 18:25:13 +0000 |
| commit | 64d28a493b8c2e63b90033ed40026c84b8fb9d9b (patch) | |
| tree | 0dc540243a2475ffa466075f667b6811ea984d11 /sys/dev/rnd.c | |
| parent | cdeeb2dd1f0747245cd979e52a13a30196091eee (diff) | |
Change arc4random_uniform() to calculate ``2**32 % upper_bound'' as
``-upper_bound % upper_bound''. Simplifies the code and makes it the
same on both ILP32 and LP64 architectures, and also slightly faster on
LP64 architectures by using a 32-bit remainder instead of a 64-bit
remainder.
Pointed out by Jorden Verwer on tech@
ok deraadt; no objections from djm or otto
Diffstat (limited to 'sys/dev/rnd.c')
| -rw-r--r-- | sys/dev/rnd.c | 15 |
1 files changed, 3 insertions, 12 deletions
diff --git a/sys/dev/rnd.c b/sys/dev/rnd.c index 9beb232b963..cb7ebe491de 100644 --- a/sys/dev/rnd.c +++ b/sys/dev/rnd.c @@ -1,4 +1,4 @@ -/* $OpenBSD: rnd.c,v 1.140 2011/07/06 14:49:30 nicm Exp $ */ +/* $OpenBSD: rnd.c,v 1.141 2012/06/24 18:25:12 matthew Exp $ */ /* * Copyright (c) 2011 Theo de Raadt. @@ -594,17 +594,8 @@ arc4random_uniform(u_int32_t upper_bound) if (upper_bound < 2) return 0; -#if (ULONG_MAX > 0xffffffffUL) - min = 0x100000000UL % upper_bound; -#else - /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ - if (upper_bound > 0x80000000) - min = 1 + ~upper_bound; /* 2**32 - upper_bound */ - else { - /* (2**32 - x) % x == 2**32 % x when x <= 2**31 */ - min = ((0xffffffff - upper_bound) + 1) % upper_bound; - } -#endif + /* 2**32 % x == (2**32 - x) % x */ + min = -upper_bound % upper_bound; /* * This could theoretically loop forever but each retry has |