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Date: Wed, 06 May 2015 09:12:05 -0400
From: Dave Angel <davea@davea.name>
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Subject: Re: Throw the cat among the pigeons
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Xref: csiph.com comp.lang.python:90056

On 05/06/2015 02:26 AM, Steven D'Aprano wrote:
> On Wednesday 06 May 2015 14:05, Steven D'Aprano wrote:

> My interpretation of this is that the difference has something to do with
> the cost of multiplications. Multiplying upwards seems to be more expensive
> than multiplying downwards, a result I never would have predicted, but
> that's what I'm seeing. I can only guess that it has something to do with
> the way multiplication is implemented, or perhaps the memory management
> involved, or something. Who the hell knows?
>

I had guessed that the order of multiplication would make a big 
difference, once the product started getting bigger than the machine 
word size.

Reason I thought that is that if you multiply starting at the top value 
(and end with multiplying by 2) you're spending more of the time 
multiplying big-ints.

That's why I made sure that both Cecil's and my implementations were 
counting up, so that wouldn't be a distinction.

I'm still puzzled, as it seems your results imply that big-int*int is 
faster than int*int where the product is also int.

That could use some more testing, though.

I still say a cutoff of about 10% is where we should draw the line in an 
interpretive system.  Below that, you're frequently measuring noise and 
coincidence.

Remember the days when you knew how many cycles each assembly 
instruction took, and could simply add them up to compare algorithms?


-- 
DaveA