func Power(base float64, exponent int) float64 {
is_minus := exponent < 0
var res float64
res = 1
var k int64
if exponent < 0 {
k = int64(-exponent)
}else {
k = int64(exponent)
}
for ; k != 0; k >>= 1 {
if k&1 ==1 {
res = res * base
}
base *= base
}
if is_minus == true {
res = 1.0/res
}
return res
}