simple log 2 calculation implement (from pintool demo)

floorLog2.c

int32_t FloorLog2(uint32_t n)
{
    int32_t p = 0;

    if (n == 0) return -1;

    if (n & 0xffff0000) { p += 16; n >>= 16; }
    if (n & 0x0000ff00) { p +=  8; n >>=  8; }
    if (n & 0x000000f0) { p +=  4; n >>=  4; }
    if (n & 0x0000000c) { p +=  2; n >>=  2; }
    if (n & 0x00000002) { p +=  1; }

    return p;
}