How to measure distance between two data

Judging from your code you assume S1/S2 are inputs each 24 bits. However I doubt it.

More likely you enter (n) elements each 24 bits wide into two rom tables (e.g. from a file).

Once you have these two roms then you read rom1 output and check each output against rom2 output until you find a match then the distance is

address2 - address1 then you perform your computation circuitry of adding all results * (n^2-1)/2

The divide by 2 is easiest(just discard 1 LSB from final result).

for n^2-1 use multiplier subtractor directly(multiply n * n) then subtract 1

for final division you will need a divider