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        riddles >> cs >> MULTIPLY WITHOUT MULTIPLYING
        
(Message started by: eviljed on Aug 9^th, 2002, 10:50am)

Title: MULTIPLY WITHOUT MULTIPLYING
Post by eviljed on Aug 9^th, 2002, 10:50am

Multiply by 8 without using multiplication or addition. Now do the same with 7.

For 8: Convert to binary. Shift left twice. That'll do it. (note that the shifts put zeros in the least significat values).

For 7: I'll have to get back to you on that.

Title: Re: MULTIPLY WITHOUT MULTIPLYING
Post by eviljed on Aug 9^th, 2002, 11:02am

I just had an ID-10T error. (aka, i'm an idiot). You shift to the left three times. Two shifts only multiplies it by 4.

Title: Re: MULTIPLY WITHOUT MULTIPLYING
Post by Aaron on Aug 9^th, 2002, 11:54am

I am assuming that addition and subtraction are different functions here...

n = (n << 3) - n;

I am still fiddling with the bits for a solution that involves no arithmatics, short of going all the way to implementing a binary subtraction function with logigates. :P

Title: Re: MULTIPLY WITHOUT MULTIPLYING
Post by -D- on Aug 9^th, 2002, 4:27pm

There is a long thread on this already furthur down the page with several ideas on it.
-D-