How do computers find modulus?

Question

Is there some cool algorithm with bit wise operations?

Answer 1

Apart from the obvious method using DIV and IDIV (for x86) as mentioned above, the result of any number modulo'd by a power of two can be calculated by taking the bitwise and: x mod y where y is pow2 is the same as x AND (y - 1). Most compilers perform this when possible, as division is far more expensive than bitwise ops