Replace the ADDER and SUBSTRACTOR

[imbichie]

Hi All,

Is there any logic which can replace the ADDER and SUBSTRACTOR from our design.

For example if there is a equation,

A = B + 97
C = D - 128

(assume A, B, C, D are in 8 bit)

Here one of the Element in the equation is a Constant.
So is there any logic to replace the ADDER and SUBSTRACTOR in this equation by using any bit Shifting method or something...

Or is there any logic so I can reduce the number of bit using for add/sub.
for example here C = D - 128
So for d'128 the LSB 7 bits are 0, so i can copy the LSB of D to C and i can use only a single bit adder/substractor.

 

[permute]

The synthesis tool should pick up the D-128 as having fewer bits for the subtract operation. 97 is just a constant, so one argument will be constant. I don't see any other optimization there.