Re: [RFC] Convert builin-mailinfo.c to use The Better String Library.

From: Andreas Ericsson <ae@op5.se>
Date: Sep 7, 2007, 11:54 UTC
Message-ID: <46E13C0F.8040203@op5.se>
In-Reply-To: <Pine.LNX.4.64.0709071155570.28586@racer.site>

Johannes Schindelin wrote:

Show 18 quoted lines

> Hi,
> 
> On Fri, 7 Sep 2007, Andreas Ericsson wrote:
> 
>> Wincent Colaiuta wrote:
>>> El 7/9/2007, a las 2:21, Dmitry Kakurin escribi?:
>>>
>>>> I just wanted to get a sense of how many people share this "Git should
>>>> be in pure C" doctrine.
>>> Count me as one of them. Git is all about speed, and C is the best choice
>>> for speed, especially in context of Git's workload.
>>>
>> Nono, hand-optimized assembly is the best choice for speed. C is just
>> a little more portable ;-)
> 
> I have a buck here that says that you cannot hand-optimise assembly (on 
> modern processors at least) as good as even gcc.
>

http://www.gelato.unsw.edu.au/archives/git/0504/1746.html

I win. Donate $1 to FSF next time you get the opportunity ;-)

Hand-optimized asm is faster because the optimizer in the compiler is a general-purpose one that has to guess and make assumptions about the code and its input to make the correct decisions. While it gets things right in as many as 80% of the cases, there's still the 20% where it doesn't. A human can, with sufficient research and effort, make the same optimizations where they are correct but avoid the 20% erroneous ones.

If the compiler gets it wrong inside your innermost loop, it might be worth shaving those extra 0.0001 seconds off of each iteration, because in the long run, world-wide, it might save several weeks worth of CPU-time every day.

-- 
Andreas Ericsson                   andreas.ericsson@op5.se
OP5 AB                             www.op5.se
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