Re: [PHP-DEV] [PATCH] random_int: Fix power of two check.

[Nikita Popov]

On Sun, May 10, 2015 at 12:40 PM, Lauri Kenttä <lauri.ken...@gmail.com>
wrote:

> (x & ~x) is always 0.
> ((x & (~x + 1)) != x) works.
> ((x & (x - 1)) != 0) works too.
> ---
>  ext/standard/random.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/ext/standard/random.c b/ext/standard/random.c
> index 12c2503..4a1adbf 100644
> --- a/ext/standard/random.c
> +++ b/ext/standard/random.c
> @@ -182,7 +182,7 @@ PHP_FUNCTION(random_int)
>         umax++;
>
>         /* Powers of two are not biased */
> -       if ((umax & ~umax) != umax) {
> +       if ((umax & (umax - 1)) != 0) {
>                 /* Ceiling under which ZEND_LONG_MAX % max == 0 */
>                 zend_ulong limit = ZEND_ULONG_MAX - (ZEND_ULONG_MAX %
> umax) - 1;
>
> --
> 2.4.0
>

Good catch, thanks! Applied via
https://github.com/php/php-src/commit/cf7e5357a46afe1dca978f4887bbd83a7507ce69
.

Nikita