Ladner Fischer adder

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lidor250

Joined Oct 2, 2021
10
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:
1671875219055.png


while in the pre-processing stage we create for each Ai, Bi :
1671875294820.png
1671875307290.png


next, in the carry generation stage we create those two:
1671875390630.png

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:
1671875530328.png

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:
1671875923315.png

1671875831041.png

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



thanks :)
 
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