>>18
I think you mean that it's equivalent to @{$x[$y]}[$z]. -> dereferences a reference, only somewhat unlike a @/$/% prefix would. I.e. $hashref->{something} works like %$hashref{something}.

>>11
They haven't listed simple instruction timings since the ppro started with the micro-ops thing. From a P2/P3 optimization manual I downloaded some years back, it seems that a "MUL eax, m/r32" instruction is decoded to 3 dependent micro-operations. (IMUL between registers decodes to just one.)

So yeah, a lot of seat-of-the-pantsing here. The point is that multiply operations are cheaper than indirecting through a pointer array, and if you're doing FP matrix computations they'll issue to the otherwise unused integer units which makes them close as can get to free.