Re: [PATCH v1 7/9] diff --color-moved-ws: optimize allow-indentation-change

From: Phillip Wood <phillip.wood@talktalk.net>
Date: Nov 17, 2018, 14:52 UTC
Message-ID: <a7ca6eef-937c-ae97-bb79-5859a2849e64@talktalk.net>
In-Reply-To: <CAGZ79ka4mHxtcwjfu3taipakUHtDXg6DjQu=nJun8Nm+snyo0g@mail.gmail.com>

On 16/11/2018 20:40, Stefan Beller wrote:

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> On Fri, Nov 16, 2018 at 3:04 AM Phillip Wood <phillip.wood@talktalk.net> wrote:
>>
>> From: Phillip Wood <phillip.wood@dunelm.org.uk>
>>
>> When running
>>
>>    git diff --color-moved-ws=allow-indentation-change v2.18.0 v2.19.0
>>
>> cmp_in_block_with_wsd() is called 694908327 times. Of those 42.7%
>> return after comparing a and b. By comparing the lengths first we can
>> return early in all but 0.03% of those cases without dereferencing the
>> string pointers. The comparison between a and c fails in 6.8% of
>> calls, by comparing the lengths first we reject all the failing calls
>> without dereferencing the string pointers.
>>
>> This reduces the time to run the command above by by 42% from 14.6s to
>> 8.5s. This is still much slower than the normal --color-moved which
>> takes ~0.6-0.7s to run but is a significant improvement.
>>
>> The next commits will replace the current implementation with one that
>> works with mixed tabs and spaces in the indentation. I think it is
>> worth optimizing the current implementation first to enable a fair
>> comparison between the two implementations.
> 
> Up to here the series looks good and I think we could take it
> as a preparatory self-standing series.

Thanks for looking at these, I think it makes sense to split the series here, the commit message for this patch may want tweaking slightly if we do. (I did wonder about splitting it in two when I submitted it but took the easy way out.)

Best Wishes

Phillip

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> 
> I'll read on.
> Thanks,
> Stefan
>