i cant understand somt part of this circuit..

**broken link removed**

its supposed to get to number and out their sum in base 5

for example 3+4=1 2

the first part of the circuit is the sum of the input number

i cant understand the next part:

what is the logic behind this gate system in between
and what is the role of the HA adders that comes after that


????

Supposedly, all the logic that follows the basic adder will conditionally adjust the output for base 5.

With decimal adjust circuits, one adds 6 to the sum digit when it is greater than 9, but add nothing if the sum is not. That will adjust the sum digit, and force a carry out for sums > 9.

Work it out in hex or binary to see that the above method works.

The base 5 circuit ought to be doing a similar thing, but with a different adjustment value.