[fpc-devel] using sse2 packed doubles

[Vincent Snijders]

Daniël Mantione wrote:
> 
> Op Sat, 7 Oct 2006, schreef Florian Klaempfl:
> 
> 
>>Vincent Snijders schrieb:
>>
>>I started to add vector pascal like support, currently only i386/x86_64 are
>>supported (no generic support). The whole (currently implemented)
>>functionality is demonstrated by the following example. Please give some
>>feedback if it allows benchmark speedups.
> 
> 
> To get a large speedup, I think you should instead of making pairs of 
> doubles, do the pixels in parallel. I.e. in this benchmark, a row is 3000 
> pixels wide, so, make an array of 3000 doubles, and do the operation with 
> arrays. With proper compiler optimization, it should be possible to 
> achieve speeds close to 2 flops a clock cycle.
> 

The 'problem' in this benchmark is that the number of iterations of the 
inner loop isn't fixed, but can vary between 1 and 50. If you pair two 
doubles, the change you can break the loop for all elements of the 
vector before iteration 50 is bigger than when you combine 3000 elements.

Vincent