take advantage of x86-64 CPU CLZ (count leading zero)
take advantage of x86-64 CPU CLZ (count leading zero)

work on #186


Former-commit-id: 3dcdb323dca92e27f5b2bc310f28123beefa7381
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin2,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin2