Hi all
as part of a project I'm working on, I need to implement Ladner Fischer adder for 8-bits with logic gates
now, I tried to search some information about implementation for that adder but there isn't a lot of information about it.

the most relevant info I found is here:
https://research.ijcaonline.org/volume79/number16/pxc3891784.pdf
https://www.ijsce.org/wp-content/uploads/papers/v3i1/A1340033113.pdf

it is explained here that the scheme is as follows:



while in the pre-processing stage we create for each Ai, Bi :




next, in the carry generation stage we create those two:


I created it for each i using the current and previous Pi,Gi created in the first stage

the only thing I didn't understand is the last stage, when we build the final sum result.
it is explained by this formula:


but there isn't a clear definition for Ci-1
I'll be glad for help for implementing this adder


here is what I did for now, trying to implement it with logisim for 4 bits:




now I'm stuck with the last stage, creating the final sum



thanks

 

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