Re: Fast copy of buffer data into a matrix

[David Bateman]

John Swensen wrote:
> Muthiah Annamalai wrote:
>   
>> I think theres something like a 
>>
>> double *val = ret_img.fortran_vec(); // in this case for Matrix,
>> what I gather from looking at liboctave/Marray2.cc|h &
>> liboctave/MArray-defs.h (where operator macros live).
>>
>> -Muthiah
>>
>>   
>>     
>>> I have searched around a bit, but can't find a way of just doing a 
>>> memcpy into the Matrix object, rather than my slow existing 
>>> implementation.  Any suggestions?
>>>
>>> John Swensen
>>> _______________________________________________
>>> Help-octave mailing list
>>> address@hidden
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>>>     
>>>       
> FYI, here is how I ended up copying a unsigned char buffer into a Matrix 
> of type uint8.  It ended up taking about 50% of the time of doing it 
> element by element.
>
> static Matrix m1(settings.width, settings.height);
> static uint8NDArray m = octave_value(m1).uint8_array_value();
> static octave_uint8* tmp = m.fortran_vec();
> memcpy( tmp, capturebuffer, settings.height*settings.width );
> return octave_value(m.transpose());   
>
>   
Shouldn't that be

static unit8NDArray m (dim_vector(settings.width, settings.height));
static octave_uint8* tmp = m.fortran_vec();
memcpy( tmp, capturebuffer, settings.height*settings.width );
return octave_value(m.transpose());

You might be able to do away with the transpose as well, as the
transpose means that there is a second copy of m in memory at the same
time. However, for it to be efficient, it would have to be some sort of
blocked algorithm so that cache limitations are taken into account..

D.

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