[RC5] Runtime optimization??

Décio Luiz Gazzoni Filho decio at decpp.net
Wed Mar 1 18:42:10 EST 2006

On Mar 1, 2006, at 8:20 PM, Fugu wrote:

> Why don't the cruncher cores compiled using fftw-like optimizations?
> Assembly code may be slightly faster, but in needs to be remade for  
> every platform...

This technique is worthwhile in FFTW (and even then, specialized  
packages handily beat FFTW) because of issues like memory/cache  
organization, size, speed, etc. RC5 is immune to those variations --  
it is only affected by register allocation and instruction scheduling.

An effective FFTW-like optimizer for RC5 would be pretty similar to a  
general C compiler's code generator/optimizer. Not only is this an  
overly complicated piece of software, but it can't schedule  
instructions all that well anyway -- just look at the performance of  
C cores. Plus I dare any compiler's code generator to produce  
something like kakace's software pipelined Altivec+integer RC5 core.

By the way, `assembly code may be slightly faster' qualifies for  
understatement of the year. Even generic assembly code, without  
targeting a specific processor, would easily beat the C cores.


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