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