Which expression is right with respect to carry look header?

Question

(i) Ci +1= Gi+ PiCi

(ii) Ci +1= G(i+1)  + P(i+1)Ci

https://www.youtube.com/watch?v=9lyqSVKbyz8&index=116&list=PLBlnK6fEyqRjMH3mWf6kwqiTbT798eAOm

i or ii ?

Answer 1

I think both are correct expressions :

Expression 1 would be true when initial cin=c0 and than from their try to calculate c1,c2,c3 and so on{i.e i>=0}

Expression 2 would be true when you take initial cin=c-1 and than c0,c1 and so on{i.e i>=-1}

Answer 2

i) is correct, reason:

Consider we are generating carry of Ci+1th term from Gith(generation ) and Pith (propagation).

Comments

@bikram sir