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How to do 255*X without a multiplier?

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anantha_09

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Without using a multiplier how could we perform 255*X?
 

Re: question

If it is digital, then you can shift left 8 times to for multiply by 256 then subtract by x. So mathematically this is x*256 - x = x*(256 - 1) = x*255 .
 

Re: question

true.

there is an official name for this kind of logic alled "canonical signed digit".

that is, for this kind of "constant * variable", you can pretty much convert this form into a series of adder and substractor instead of using an multiplier. For certain types of constants, it will save a lot of areas. The optimal form is called "cononical signed digit".

Just like what heyheyhey replied, his form is cononical.
 

Re: question

let me confirm onething

if a number is shifted left it is multiplied

and if shifted right it is divided

is this rite?


any material on this kind of stuff would be of great help
 

Re: question

why don't you shift a number on paper, and find out for yourself?

just convert a decimal number to binary ... left shift it once ... and reconvert it back to decimal... what do you get??

do the same for right shifts...
 

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