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16 lines
400 B
Go
16 lines
400 B
Go
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// +build !amd64 appengine popcntgo
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package bits
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// Popcnt counts the number of bits set
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func Popcnt(x uint64) uint64 {
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// bit population count, see
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// http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
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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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