[Gdal-dev] [RFC] RasterIO speedup patch

[Tim Beckmann]

Frank, 

No problem on the delay.  I understand having a large mail queue (I've 
never seen so much traffic on the gdal list as there has been lately ;). I 
haven't had time since I sent the email to work on the GDALCopyWords 
anyway.  That's why I didn't poke you sooner.

I didn't receive an email that my patch had been applied.  I assumed the 
submitter would automatically be notified.  Not a big deal - now I know 
;).  Thanks to you and Andrey for applying it.

I'll make sure my follow-on patch(es) test for pointer alignment (will be 
a little bit yet before I find the time to finish the patches).

Thanks
Tim
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Tim Beckmann               tbeckman at usgs.gov
Software Project Lead
SAIC
EROS Data Center, Sioux Falls, SD 57198
605-594-2521    Phone
605-594-6940    Fax





Frank Warmerdam <warmerdam at pobox.com>
Sent by: gdal-dev-admin at remotesensing.org
02/18/2003 08:46 AM
Please respond to gdal-dev

 
        To:     gdal-dev at remotesensing.org
        cc: 
        Subject:        Re: [Gdal-dev] [RFC] RasterIO speedup patch


Tim Beckmann wrote:
> Resend... Frank, you didn't reply to this email and it has a question in 

> that I need an answer to...

Tim,

Sorry about that.  Approximately 1400 "in queue" email message fell into 
an
HD black hole a week and a half ago.

> Okay, I put it in bugzilla.  It is #281.

As noted in Bugzilla Andrey has applied your patch.

> I still need to clean up the other changes a bit before I submit them. 
One 
> question for you.  When GDALCopyWords does data type conversions, it 
uses 
> memcpy for copying out a single data element at a time.  The only reason 
I 
> can think of why this would be done is that you're worried about being 
> given data buffers that aren't properly aligned in memory for platforms 
> that have such limitations.  Is this correct?  The next set of changes 
> assumes memory alignment is correct.  I can either try using memcpy and 
> see if it impacts speed in my changes, or I can make it one more special 

> case that the changes I've done are only used when memory alignment 
> constraints are met.  Actually, I can't think of a case where memory 
> wouldn't be correctly aligned when going through RasterIO.  But I 
suppose 
> someone could end up with incorrectly aligned buffers when calling 
> GDALCopyWords directly (but for efficiency maybe it should just error 
out 
> in that case and the driver should be fixed).

GDALCopyWords() is sometimes used to copy data out of buffers read from 
disk
that are not word aligned, so this is an issue.  I think that if you want 
to
copy by word in some cases then GDALCopyWords() should verify that the
pointer is word aligned.

Don't hesitate to poke me when I don't respond in a day or two to a 
question.

Best regards,

-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, 
warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent


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