Re: Is ther any sense in *= and matrices?

[Ole Kristensen <ole@linux.local>]

Wesley Groleau <wesgroleau@despammed.com> writes:

> > Yes, on modern hardware, having a pointer for each row of the matrix
> > usually leads to slower code. The reason is that the indexing
> > operation by multilply/add is actually faster than fetching a pointer
> > from an array and then adding, thereby incurring an extra memory fetch
> > and cache pollution. The above holds for large matrices, I haven't
> 
> So Java's handling of arrays is inefficient
> for matrices, even if bypassing the JVM by
> compiling to native code?

Can't speak for Java, but when I tried a 128**3 matrix in Ada and C++,
the plain indexing scheme beat the clever pointer array by a
significant amount. This was on a 1.8GHz Pentium 4. I cannot say
anything definite about other systems, but in general, it pays to
think a lot about memory access patterns on fast CPU's.