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18 lines
514 B
18 lines
514 B
7 years ago
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// +build !go1.9
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package roaring
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// bit population count, take from
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// https://code.google.com/p/go/issues/detail?id=4988#c11
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// credit: https://code.google.com/u/arnehormann/
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// credit: https://play.golang.org/p/U7SogJ7psJ
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// credit: http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
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func popcount(x uint64) uint64 {
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x -= (x >> 1) & 0x5555555555555555
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x = (x>>2)&0x3333333333333333 + x&0x3333333333333333
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x += x >> 4
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x &= 0x0f0f0f0f0f0f0f0f
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x *= 0x0101010101010101
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return x >> 56
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}
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