46 lines
628 B
Go
46 lines
628 B
Go
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package bitset
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func select64(w uint64, j uint) uint {
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seen := 0
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// Divide 64bit
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part := w & 0xFFFFFFFF
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n := uint(popcount(part))
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if n <= j {
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part = w >> 32
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seen += 32
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j -= n
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}
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ww := part
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// Divide 32bit
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part = ww & 0xFFFF
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n = uint(popcount(part))
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if n <= j {
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part = ww >> 16
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seen += 16
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j -= n
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}
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ww = part
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// Divide 16bit
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part = ww & 0xFF
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n = uint(popcount(part))
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if n <= j {
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part = ww >> 8
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seen += 8
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j -= n
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}
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ww = part
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// Lookup in final byte
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counter := 0
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for ; counter < 8; counter++ {
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j -= uint((ww >> counter) & 1)
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if j+1 == 0 {
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break
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}
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}
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return uint(seen + counter)
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}
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