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SubjectRe: Big git diff speedup by avoiding x86 "fast string" memcmp
On 12/15/2010 08:00 PM, David Miller wrote:
> From: Boaz Harrosh <>
> Date: Wed, 15 Dec 2010 15:15:09 +0200
>> I agree that the byte-compare or long-compare should give you very close
>> results in modern pipeline CPUs. But surly 12 increments-and-test should
>> show up against 3 (or even 2). I would say it must be a better plan.
> For strings of these lengths the setup code necessary to initialize
> the inner loop and the tail code to handle the sub-word ending cases
> eliminate whatever gains there are.

You miss understood me. I'm saying that we know the beggining of the
string is aligned and Nick offered to pad the last long, so surly
a shift by 2 (or 3) + the reduction of the 12 dec-and-test to 3
should give you an optimization?

> I know this as I've been hacking on assembler optimized strcmp() and
> memcmp() in my spare time over the past year or so.


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