Re: [PATCH] sha1_name: make wraparound of the index into ring-buffer explicit

From: Jeff King <peff@peff.net>
Date: Nov 1, 2016, 15:04 UTC
Message-ID: <20161101150429.fohpchtlfvohzood@sigill.intra.peff.net>
In-Reply-To: <a1e2c4a4-4720-fc26-c866-6ab959543c3b@web.de>

On Tue, Nov 01, 2016 at 09:49:07AM +0100, René Scharfe wrote:

> Overflow is defined for unsigned integers, but not for signed ones.
> Wrap around explicitly for the new ring-buffer in find_unique_abbrev()
> as we did in bb84735c for the ones in sha1_to_hex() and get_pathname(),
> thus avoiding signed overflows and getting rid of the magic number 3.

Thanks. I didn't mean to make you do this, but my procrastination won again.

Show 11 quoted lines

> diff --git a/sha1_name.c b/sha1_name.c
> index 06409a3..73a915f 100644
> --- a/sha1_name.c
> +++ b/sha1_name.c
> @@ -510,7 +510,8 @@ const char *find_unique_abbrev(const unsigned char *sha1, int len)
>  {
>  	static int bufno;
>  	static char hexbuffer[4][GIT_SHA1_HEXSZ + 1];
> -	char *hex = hexbuffer[3 & ++bufno];
> +	char *hex = hexbuffer[bufno];
> +	bufno = (bufno + 1) % ARRAY_SIZE(hexbuffer);

Code looks obviously correct (and it even does the "start at 0" thing).

-Peff