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Re: slow char({str})
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From: |
Jaroslav Hajek |
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Subject: |
Re: slow char({str}) |
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Date: |
Wed, 24 Jun 2009 08:39:13 +0200 |
On Wed, Jun 24, 2009 at 8:34 AM, Daniel J Sebald<address@hidden> wrote:
> Jaroslav Hajek wrote:
>
>>>> Please check
>>>> http://hg.savannah.gnu.org/hgweb/octave/rev/4ff6f8efdda2
>>>>
>>>> also transplanted into 3.2.x.
>>>>
>>>> thanks
>>>
>>> Very nice Jaroslav. Which of these changes is the speedup coming from?
>>> This hunk
>>>
>>> - elem (i, j) = s[i][j];
>>> + elem (i, j) = si[j];
>>>
>>> shouldn't have been too much as there is only a little extra computation
>>> in
>>> the indexing before the change.
>>
>>
>> No. In fact, this *was* the bottleneck, changing a linear complexity
>> operation to quadratic one. Welcome to the world of COW magic.
>
> Oh yeah, s is a reference, not a pointer...
>
> What does COW stand for, other than can of worms?
>
> Dan
>
Copy-On-Write
--
RNDr. Jaroslav Hajek
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz