SmallIntPair as immediate word

 
All,

Squeak release image contains around 15k Points with none using more
than 24 bits per coordinate.

On 64-bit machines, it should be possible to pack two integers of a pair
into a single immediate word - 30+30.

Has anyone tried to do this? It would save space and eliminate object
alloc. But I am not sure about the overall performance hit.

Regards .. Subbu

 
Hi Subbu,


I'm _really_ interested how you arrived at those numbers. Can you share the code for your analysis?

Best regards
        -Tobias

 
On 10/04/19 12:44 AM, Tobias Pape wrote:
Squeak 5.2 (Linux 64b) #18231

{Point. Fraction} collect: [:c | c allSubInstances size]
    #(12118 32)

Point allSubInstances select: [ :p | (p x >= (2 raisedTo: 24)) or: (p y
 >= (2 raisedTo: 24))]
        an OrderedCollection ()
Fraction allSubInstances select: [ :p | (p numerator >= (2 raisedTo:
24)) or: (p denominator >= (2 raisedTo: 24))]
        an OrderedCollection ()

Regards .. Subbu

 
Tobias Pape <[hidden email]> wrote:
>  
Hi Subbu,


Does that hold when using 8K displays?

Stephan

 
Hi Subbu,

> On Apr 9, 2019, at 9:44 AM, K K Subbu <[hidden email]> wrote:
>
> All,
>
> Squeak release image contains around 15k Points with none using more than 24 bits per coordinate.
>
> On 64-bit machines, it should be possible to pack two integers of a pair into a single immediate word - 30+30.

Yes, but not without losing the single bit tag tests the 64-bit VM uses now.  So doing this would reduce slightly the efficiencies of SmallInteger, Character and SmallFloat64.  And performance for these classes is much more important than making point devise more complex, in the image and in graphics plugins.

>
> Has anyone tried to do this? It would save space and eliminate object alloc. But I am not sure about the overall performance hit.

I think these kinds of things don’t work well in practice.  And as Stephan points out we are two generations of display technology away from not being able to use such compact points to represent the entire display coordinate space.

At this stage it’s better to invest in more powerful and more general optimization strategies; ie Sista/Scorch.  With Clément leaving for google, hopefully only for a few years, I could do with competent help here.

>
> Regards .. Subbu

 
On 10/04/19 4:03 PM, Stephan Eggermont wrote:
Yes. 8K is 7680 x 4320 - 13bits each for x and y. That is just 13bits
for x and y. In any case, if any integer in a pair overflows, it will be
stored in a heap object.

Regards .. Subbu