How to measure distance between two data

Ok you are getting there. Your read can be internal rather than inputs.

I suggest state machine of s0,s1,s2

s0: read ram1(address at 0) into ram1_data register, one clock,move to s1

s1:read ram2(address 0~till equality) into ram2 register, several clocks, if equality found between ram1/ram2 data set ram2 address

to zero, output (address difference), move to s2

s2:set ram1 address to 1(increment),one clock, move to s0

start again for ram1 address 1 and so on.

by doing that you will output a stream of distance.

Your design is no trivial and is good for practice.