function of multipliers

function of multipliers

Post by Thomas Gutzle » Fri, 24 Oct 2003 18:38:54


is there a chance to get the functions that describe the single output
bits of a 32 bit adder/multiplier.
out1 = f(in1, in2, in3, .. in32)
out32 = f(in1, in2, in3, .. in32)

It's easy to generate the functions for < 10 bit by using truthtables
and logic-minimization tools but the truth table for a 32 bit
adder/multiplier gets quite large :)
So I thought there must be another way.



1. costs of indirect function calls vs. direct function calls

Does anyone have any idea what the cost of an indirect vs. direct function call
would be for various implementations?

Near as I can figure, for an indirect jump you're going to do (on a RISC)
- load address
- [possibly transfer address to some register]
- jump to address register.


- jump PC + offset

Potential differences are:
- extra load [d-cache miss]
- mispredict penalty of branch-target-address cache vs. mispredict penalty of
branch prediction
- function call address generation

Any ideas what the actual numbers are?


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