Roey, I think you're right on here.
The default zeroes/zeros uses the PP threading engine to loop over the
elements, well, elementwise - ie byte by byte. The string assignment uses an
optimized memory copy that is part of Perl and almost certainly does things
word by word. On a 64 bit machine, that means zeroes does 8x more work than it
has to in this specific case.
This is a good idea for a fix. There are probably more pressing things that
need to be finished first (I'm "only" 9 months behind on getting the
core-cleanup branch clang-clean, for example), but it's a localized patch to
zeroes and ones if someone wants to make it.
Cheers,
Craig
On Sep 18, 2014, at 5:22 AM, Roey Almog (Infoneto Ltd) <al...@infoneto.co.il>
wrote:
> Hi,
>
> I am a bit new to PDL so if the answer is obvious I have missed it some how...
>
> I have around 1 million vectors of about 1 million elements long each element
> is one byte in size
>
> The information is streamed in, one vector at a time with input data - the
> data itself is not read from a file its real life information collected so
> every time I run the program I get something else.
>
> I found that initializing the vectors with zeros takes long time, seems that
> zeros iterates on all the cells settings them to zero
>
> so I created any empty pdl with zeros and each time I need to create a PDL I
> use
> this methos
>
> # this is done once
> my $pdl_template = zeros(byte, $size);
> my $buffer_template = $pdl_template->get_dataref;
>
>
> # now when getting the information
> my $pdl = PDL->new_from_specification(byte, $size);
> my $ptr_buffer = $pdl ->get_dataref;
> $$ptr_buffer = ${$buffer_template};
> $pdl->upd_data;
>
> This is about 7 times faster than zeros, however it would be better if zeros
> (and also ones) had some optimization to clear an empty vector even faster
> using c's memset function when applicable (bytes. shorts integer etc.)
>
> As this seems very useful I wonder if I missed something ?
>
> Thanks
> Roey
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