Where to store s-boxes for a cipher?

Discussion created by michaelhuber on Nov 2, 2010
Latest reply on Dec 10, 2010 by frankas

hello to everybody, it's my first posting here.

i am currently coding a blockbased implementation of a block-cipher that uses a standard s-box (8x8), so 8 bit input and 8 bit output. in every single round of the block-cipher i have to access to a s-box, which consists of 256 entries and therefore can be adressed with one byte.

i definitly need indexed access to a "memory" where the s-box lies, fastest access as possible.

currently i am using a temp-index-array, so i can access an element with x0[240] for example.

my problem is though that there will be a need of 256 registers which can't be covered by the 128 registers. the compiler seems to swap them out to scratch-registers.

any ideas, how to access an "indexed array" with fastest access as possible?


thanks in advance