Multiply with negative integer just by shifting.

Posted by stex on Stack Overflow See other posts from Stack Overflow or by stex
Published on 2010-05-01T21:21:59Z Indexed on 2010/05/01 21:27 UTC
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Hi,

I'm trying to find a way to multiply an integer value with negative value just with bit shifting.

Usually I do this by shifting with the power of 2 which is closest to my factor and just adding / subtracting the rest, e.g. x * 7 = ((x << 3) - x)

Let's say I'd want to calculate x * -112. The only way I can imagine is -((x << 7) - (x << 4), so to calculate x * 112 and negate it afterwards.

Is there a "prettier" way to do this?

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