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I have been trying to understand some equations mentioned in AN404, I was wondering whether someone can help me out.

The equations are: P = ceil(log4(N)) R = 1 if log2(N) is odd and 0 if log2(N) is even (1) Single output engine: maximum: -3P+R minimum: P+R-4 (2) Quad output engine: maximum: -3P+R+1 minimum: P+R-7 or (P+R-4)-3 I know that:- P is equal to the number of 4 input butterflies
- R is the# of 2-input butterfly that is needed, i.e. if log2(N) is even, then you do not need 2-input butterfly.

- -3P (for total# of multiplier in the 4-input butterflies)
- + R (in a 2 input butterfly, you either add or subtract, and the subtraction can potentially decrease the scaling value).

- P + R is the total# of stages, it is assuming that scaling value can go up by one at each stage.

- Why single output engine is three more than quad output?
- Also where does the -4 come from?

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I think I figured out those equations myself...

Minimum:- Single: -3P + R
- Quad: -3P + R + 1

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