23 lines
439 B
Go
23 lines
439 B
Go
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package popcount
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// pc[i] is the population count of i.
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var pc [256]byte
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func init() {
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for i := range pc {
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pc[i] = pc[i/2] + byte(i&1)
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}
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}
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// PopCount returns the population count (number of set bits) of x.
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func PopCount(x uint64) int {
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return int(pc[byte(x>>(0*8))] +
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pc[byte(x>>(1*8))] +
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pc[byte(x>>(2*8))] +
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pc[byte(x>>(3*8))] +
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pc[byte(x>>(4*8))] +
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pc[byte(x>>(5*8))] +
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pc[byte(x>>(6*8))] +
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pc[byte(x>>(7*8))])
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}
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