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Re: Chunk Array Decimation [message #32377 is a reply to message #32363]

Fri, 04 October 2002 15:07

JD Smith
Messages: 850
Registered: December 1999

Senior Member

One more very depressing timing to report. I compiled a C version of
the literal accumulate loop, which consists entirely of:

for(i=0;i<=n_elts-1;i++) vec[inds[i]]+=data[i];

(omitting 10 lbs of DLM cruft). Here's a test run with 1,000,000
elements, each index repeated 20 times on average:

Literal Accumulate Loop: 1.2411
Reverse Indices Loop: 0.7217
Loop-Free with Sparse Arrays: 1.1401
FDDRIZZLE Loop: 0.7815
Dual Histogram Loop: 0.5490
Thinned WHERE Histogram Loop: 0.8422
Literal Accumulate: Compiled DLM : 0.0288

Yes, that's right, 20 times faster than the fastest pure IDL method.
What's really amusing is to compare the compiled and uncompiled
Literal Accumulate Loop, which uses precisely the same logic: 43 times
faster, which is the approximate penalty you pay for loops in IDL
vs. loops in C. This is optimized C (whereas IDL is not heavily
optimized), but it only uses one processor. Threads are not enough to
recover the tremendous difference between native compiled and IDL
code.

I discover this disparity about once every year, and then conveniently
forget about it, lest I should spend too much time writing function
declarations ;).

JD

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[Message index]

		Chunk Array Decimation By: JD Smith on Tue, 01 October 2002 12:32
		Re: Chunk Array Decimation By: JD Smith on Fri, 04 October 2002 15:07
		Re: Chunk Array Decimation By: Jaco van Gorkom on Mon, 07 October 2002 08:51
		Re: Chunk Array Decimation By: JD Smith on Wed, 09 October 2002 17:18
		Re: Chunk Array Decimation By: JD Smith on Wed, 09 October 2002 17:19
		Re: Chunk Array Decimation By: Jaco van Gorkom on Thu, 10 October 2002 07:26
		Re: Chunk Array Decimation By: JD Smith on Thu, 10 October 2002 11:51
		Re: Chunk Array Decimation By: Keflavich on Tue, 18 November 2008 07:21
		Re: Chunk Array Decimation By: Wout De Nolf on Tue, 18 November 2008 02:52
		Re: Chunk Array Decimation By: Keflavich on Mon, 17 November 2008 13:40

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