[Numpy-discussion] numexpr thoughts

[Tim Hochberg]

David M. Cooke wrote:

>On Tue, Mar 07, 2006 at 11:33:45AM -0700, Tim Hochberg wrote:
>  
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>>Tim Hochberg wrote:
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>>>>3. Reduction. I figure this could be done at the end of the program in
>>>> each loop: sum or multiply the output register. Downcasting the
>>>> output could be done here too.
>>>>
>>>>        
>>>>
>>I'm still not excited about summing over the whole output buffer though. 
>>That ends up allocating and scanning through a whole extra buffer which 
>>may result in a signifigant speed and memory hit for large arrays. Since 
>>if we're only doing this on the way out, there should be no problem just 
>>allocating a single double (or complex) to do the sum in.  On the way 
>>in, this could be set to zero or one based on what the last opcode is 
>>(sum or product). Then the SUM opcode could simply do something like:
>>    
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>
>No, no, we'd just sum over the 128 element output vector (mem[0]), and
>add the result to cumulative sum. That vector should already be in
>cache, as the last op would put it there.
>  
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Ah! Ok then. That's what I was thinking of too. For some reason I 
thought you were proposing building the whole result vector then summing it.

Here's another wrinkle: how do we deal with:

 >>> a = reshape(arange(9), (3,3))
 >>> sum(a)
array([ 9, 12, 15])


Just forbid it? For the time being at least?

>  
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>>BTW, the cleanup of the interpreter looks pretty slick.
>>    
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>Not finished yet :-) Look for a checkin today (if I have time).
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They didn't seem to have any speed advantage, so I ripped out all the 
compare with constant opcodes amd used COPY_C instead. I'm probably 
going to rip out OP_WHERE_XXC and OP_WHERE_XCX depending on the timings 
there. Should I also kill OP_ADD_C and friends as well while I'm at it?

-tim