Question

I try to determine the right most nth bit set

if (value & (1 << 0)) { return 0; }
if (value & (1 << 1)) { return 1; }
if (value & (1 << 2)) { return 2; }
...
if (value & (1 << 63)) { return 63; }

if comparison needs to be done 64 times. Is there any faster way?

Answer 1

Works for Visual C++ 6

int toErrorCodeBit(__int64 value) {
    const int low_double_word = value;
    int result = 0;

    __asm
    {
        bsf eax, low_double_word
        jz low_double_value_0
        mov result, eax
    }
    return result;

low_double_value_0:    
    const int upper_double_word = value >> 32;

    __asm
    {
        bsf eax, upper_double_word
        mov result, eax
    }
    result += 32;
    return result;
}