Re: [PATCH 1/1] Bypass expensive content comparsion during rename detection.

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Dec 14, 2006, 11:18 UTC
Message-ID: <Pine.LNX.4.63.0612141214440.3635@wbgn013.biozentrum.uni-wuerzburg.de>
In-Reply-To: <20061214110858.GE1747@spearce.org>

Hi,

On Thu, 14 Dec 2006, Shawn Pearce wrote:

Show 6 quoted lines

> My first version of the patch had the hash comparsion right after we 
> called diff_populate_filespec to get the size data.  But then I realized 
> that very often the sizes will be different and the src->size != 
> dst->size comparsion will tend to be true most of the time, thus saving 
> us a (relatively) expensive hash comparsion, which we know must fail 
> anyway if the sizes differed.

Ah! I misunderstood. Since the call to diff_populate_filespec was not visible in the hunk, I erroneously assumed that you meant to _check_ the sizes before checking the hashes.

But your explanation makes lots of sense to me. May I request a short comment above the new code, like "let diff_populate_filespec() do its thing since we need the filesize later on anyway, and having that, do the cheaper filesize check before the more expensive hashcmp()"?

Ciao, Dscho