AVR-Chat

Dear all,

 I've long been a user of C on AVRs, but now I have need for speed, and I'm
kinda stuck :-)
I have a two dimensional array, called array[16, 256], stored in flash
memory (these vaules won't change).
and what I need to do is something like this ;-

PORTD = array[num, step] ; // C psuedo code

The array contains only 8 bit values,  but these are organised as 16 lots of
256 bytes.
Any suggestions how, given that both 'num' and 'step' are variables held in
ram.

Thanks in advance
Paul