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package goja
// inspired by https://gist.github.com/orlp/3551590
var overflows = [64]int64{
9223372036854775807, 9223372036854775807, 3037000499, 2097151,
55108, 6208, 1448, 511,
234, 127, 78, 52,
38, 28, 22, 18,
15, 13, 11, 9,
8, 7, 7, 6,
6, 5, 5, 5,
4, 4, 4, 4,
3, 3, 3, 3,
3, 3, 3, 3,
2, 2, 2, 2,
2, 2, 2, 2,
2, 2, 2, 2,
2, 2, 2, 2,
2, 2, 2, 2,
2, 2, 2, 2,
}
var highestBitSet = [63]byte{
0, 1, 2, 2, 3, 3, 3, 3,
4, 4, 4, 4, 4, 4, 4, 4,
5, 5, 5, 5, 5, 5, 5, 5,
5, 5, 5, 5, 5, 5, 5, 5,
6, 6, 6, 6, 6, 6, 6, 6,
6, 6, 6, 6, 6, 6, 6, 6,
6, 6, 6, 6, 6, 6, 6, 6,
6, 6, 6, 6, 6, 6, 6,
}
func ipow(base, exp int64) (result int64) {
if exp >= 63 {
if base == 1 {
return 1
}
if base == -1 {
return 1 - 2*(exp&1)
}
return 0
}
if base > overflows[exp] || -base > overflows[exp] {
return 0
}
result = 1
switch highestBitSet[byte(exp)] {
case 6:
if exp&1 != 0 {
result *= base
}
exp >>= 1
base *= base
fallthrough
case 5:
if exp&1 != 0 {
result *= base
}
exp >>= 1
base *= base
fallthrough
case 4:
if exp&1 != 0 {
result *= base
}
exp >>= 1
base *= base
fallthrough
case 3:
if exp&1 != 0 {
result *= base
}
exp >>= 1
base *= base
fallthrough
case 2:
if exp&1 != 0 {
result *= base
}
exp >>= 1
base *= base
fallthrough
case 1:
if exp&1 != 0 {
result *= base
}
fallthrough
default:
return result
}
}
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