Quote:

>>I am trying to use the mod operator in my VHDL code, but my synthesis tool

>>only supports X MOD Y; where Y is a power of 2; X an integer.

>>What would be the equivalency between X MOD 255 and X MOD 256 ?

>>I would also like to find the equivalency between X MOD (2**m - 1) and

>>X MOD (2**m); where m is an integer.

There's not really any equivalency; knowing X mod 256 doesn't

help you compute X mod 255 in the general case.

However your problem is simpler if the range of X is restricted.

For example, If as I suspect you're doing Galois-field

operations, you might need to take X mod 255 where X is in

the range 0 through 509. In that case

X mod 255 = X (if X < 255)

X-255 (otherwise)

Hope this helps a bit --

Steve