[Boost-users] R: [multi-array] Performance? Difference from GIL or uBLAS?

From: Andrea Denzler (andrea_at_[hidden])
Date: 2008-08-07 14:00:59

> > It seems like the trend in image 
> > processing is to avoid using indexes in the inner loop if at all
possible.
> Which is a non sensical way of doing stuff cause code using pointer
arithmetic and "leet" stuff like *(ptr++ + x*width) makes code hard to
decipher and > to parallelize afterward.
> I wish you a good deal of fun to block a pointer based IP code into SMP or
SIMD :/ 
> It's preferable to stick to indexes as it works fine on both side
(parallelization and performances).

But with a index you need two variables, the base pointer + index. And
unless your compiler + instruction set allows you to addess a memory
location using a base pointer + index then you are going to loose much in
performance. IMHO a pointer is always faster, it let you write the algorithm
in a different way avoiding probably the example you gave above.