DateAndTime hash was: Re: [squeak-dev] true hash

Levente Uzonyi leves at elte.hu
Mon May 14 03:04:04 UTC 2012


On Sat, 12 May 2012, Andres Valloud wrote:

> When asserting speedups and collision rates, please also mention what was the 
> dataset used for the measurements.  In that way, others can replicate the 
> results and compare hash functions on a consistent basis.

+1. I started hacking it a bit and got another ~2x speedup on my 
benchmark, but it was too simple and I didn't have the time to dig deeper.


Levente

>
> On 5/10/12 6:21 , Paul DeBruicker wrote:
>> On 05/10/2012 04:21 AM, Nicolas Cellier wrote:
>>> Sure, I already changed various Number>>hash and could as well change
>>> Point hash to follow recommendations from Andres valloud book hashing
>>> in smalltalk...
>>> 
>>> Nicolas
>> 
>> DateAndTime>>#hash could be changed to :
>> 
>> hash
>> 	^ (jdn hashMultiply bitXor: seconds + offset asSeconds) bitXor: nanos
>> 
>> which is 130x faster than whats currently in the image:
>> 
>> hash
>> 	^ self asUTC ticks hash
>> 
>> 
>> The collision rate on the proposed hash function is 0.04% ( 4 per 10,000 )
>> 
>> 
>
>


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