diff options
| author | Cœur <coeur@gmx.fr> | 2023-03-02 12:41:11 +0800 |
|---|---|---|
| committer | Azat Khuzhin <azat@libevent.org> | 2023-03-02 07:51:14 +0100 |
| commit | 557990cad33f1b06a1e2a416231d79590237dd2e (patch) | |
| tree | 08040d1c1ec1ef7118d33c0e669179a0f86d6080 | |
| parent | e96e98aea5ed9f69641e74b39153747218990bdc (diff) | |
| download | libevent-557990cad33f1b06a1e2a416231d79590237dd2e.tar.gz | |
Optimize arc4random_uniform() (by syncing with OpenBSD implementation)
1. In d4de062, in Feb 2010, libevent adopted OpenBSD implementation of
arc4random_uniform.
2. In
https://github.com/openbsd/src/commit/728918cba93e0418bea2a73c9784f6b80c2a9dbd,
in Jun 2012, OpenBSD improved their implementation to be faster, by
changing arc4random_uniform() to calculate ``2**32 % upper_bound'' as
``-upper_bound % upper_bound''.
Alternatively we can simply remove arc4random_uniform() since it is not
used by libevent anyway, but let's just sync the header for now.
| -rw-r--r-- | arc4random.c | 13 |
1 files changed, 2 insertions, 11 deletions
diff --git a/arc4random.c b/arc4random.c index b3ec7655..21a12755 100644 --- a/arc4random.c +++ b/arc4random.c @@ -506,17 +506,8 @@ arc4random_uniform(unsigned int upper_bound) if (upper_bound < 2) return 0; -#if (UINT_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 * 2)) % x == 2**32 % x when x <= 2**31 */ - min = ((0xffffffff - (upper_bound * 2)) + 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 |