Help with JavaME Function

Could anyone explain to me how this MIDP Java function works? I'm particularly curious about the operators being used.

public 开发者_开发百科static final int smoothDivide(int numerator, int denominator) {
    return (int) ((numerator << 16) / denominator + 32768L) >> 16;
}

Thanks a lot

This is a division algorithm that rounds to the closest integer. It is equivalent to

Math.round((float) numerator / denominator)

for a large range of the integers, but cleaverly implemented without floating point operations.

The operators << and >> are bitwise shift left and shift right operators.

Here is the intuition for how it works

First note that << 16 and >> 16 are equivalent to * 65536 and / 65536 respectively. So what the algorithm computes is the folowing:

            / numerator * 65536           \
result  =  ( ------------------  +  32768  )  /  65536
            \   denominator               /

That is, it scales up the numerator, divides it, adds half of the scale, and then scales it down again.

It is similar to the expression (int) ((numerator + 0.5) / denominator) which is a more common way to do "rounded" division (but it relies on floating point arithmetic).