[Vm-dev] Re: Nice bit trick for component add

Eliot Miranda eliot.miranda at gmail.com
Wed Dec 25 05:52:26 UTC 2013

On Tue, Dec 24, 2013 at 1:35 PM, Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> wrote:

> Sure, I agree but this would require platform specific code...
> As I developped in the other thread, an alternative is to use native
> libraries where possible - that is when they perform an equivalent job (It
> would be Quartz or something like that for me).
> Such platform specific support will be harder to obtain, because it
> requires knowledge of VM plugin+external library or low level assembler...
> Plus the pain of diving into historical VM architecture (specifically in
> BitBlt, it's not that easy to get the full picture when you did not
> participate to the development - like me).
> I note that there is plenty of work required in this area, sort of
> technical debt. For example my MacOSX VMs do not support the little endian
> image formats yes (those with negative depth) which could be surprising if
> we didn't knew historical roots...
> ^Display supportedDisplayDepths
> So, in a word, such platform specific support can certainly provide great
> rewards, but with significative investments.
> On the other hand, these little tricks are like harvesting low hanging
> fruits.
> They are made of pure C^H slang, thus valid on every platform which does
> not yet provide specific accelerated support.
> I'm lazy and just musing, so the fastest ROI is appealing.
> Remember my little text composition/display benchs?
>     | text canvas m1 |
>     canvas := FormCanvas extent:  569 at 399 depth: 32.
>   text := Compiler evaluate: (FileStream fileNamed: 'text.st')
> contentsOfEntireFile.
>     m1 := TextMorph new.
>     m1 text: text textStyle: TextStyle default.
>     m1 wrapFlag: true.
>     m1 extent: 569 at 9999999.
>    MessageTally spyOn: [ Time millisecondsToRun: [100 timesRepeat: [
>         m1 drawOn: canvas]]]
>  Interpreter VM 4.10.10 Before bit hacks: 1425 1411 1403
>  Interpreter VM After bit hacks: 1152 1173
> 15 to 20% less, it's not really impressive, but the hurdle is low, just
> two bit-hacks applied to rules 20 24 30 & 31

On the contrary.  That kind of speed-up in a mature tuned numerical
algorithm is impressive.  Thanks!

> 2013/12/24 tim Rowledge <tim at rowledge.org>
>> If you (or anyone else, of course) are interested in really speeding up
>> bitblt, it would likely be worth looking at the ARM specific speedups Ben
>> Avison did for the PI. (Look in platforms/Cross/plugins/BitBltPlugin) and
>> seeing if similar tricks could be done with the assorted media instructions
>> in current i7 etc cpus.
>> tim
>> --
>> tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
>> Experience is something you don't get until just after you need it.
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