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## #1 2005-04-06 11:30:18

AV
Guest

### mod of 3

You are given a number n and you have to find if its divisble by 3 but the catch is you cant use mod or division operations
i am looking for something using binary arithmetic

## #2 2005-04-06 11:51:06

MathsIsFun
Registered: 2005-01-21
Posts: 7,691

### Re: mod of 3

I recall using integer division in the past. It had special methods that may suit you.

Now if I could only find what I did with it ....

... I did find this: http://www.bearcave.com/software/divide.htm , the author has some C code that might do it for you.

The central part of his code has:

while (remainder < divisor) {
bit = (dividend & 0x80000000) >> 31;
remainder = (remainder << 1) | bit;
d = dividend;
dividend = dividend << 1;
num_bits--;
}

(he says that always goes one step too far, so he just backs up once.)

Is that what you were looking for?

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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