# getting just the sign of the result from a dot product

I'm implementing a dot unit in an electrical design, but I'm only interested in the sign of the result and not the magnitude. Is there a way to reduce the number of mathematical operations (mainly the multiplication operations) to get just the sign faster and with less space?

Right now I'm calculating it using: (a1,b1,c1).(a2,b2,c2)=a1.a2+b1.b2+c1.c2.

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Anything special about your vectors? – J. M. May 3 '11 at 13:56

## 1 Answer

Not really.

Compare

(10,20,29).(40,10,-20) = +20
(10,20,30).(40,10,-20) = 0
(10,20,31).(40,10,-20) = -20

and there are no obvious shortcuts to find the signs.

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