89 lines
1.5 KiB
Go
89 lines
1.5 KiB
Go
package rlepluslazy
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type rbitvec struct {
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index int
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bits uint16
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bitCap byte
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vec []byte
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}
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func readBitvec(vec []byte) *rbitvec {
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bv := &rbitvec{vec: vec}
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if len(vec) > 0 {
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bv.bits = uint16(bv.vec[0])
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}
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return bv
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}
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const (
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minCap = 8
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maxCap = 16
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)
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var bitMasks = [9]byte{
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0x0,
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0x1,
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0x3,
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0x7,
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0xF,
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0x1F,
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0x3F,
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0x7F,
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0xFF,
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}
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func (bv *rbitvec) Get(count byte) byte {
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res := byte(bv.bits) & bitMasks[count]
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bv.bits = bv.bits >> count
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bv.bitCap = bv.bitCap - count
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if bv.index < len(bv.vec) {
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bv.bits = bv.bits | uint16(bv.vec[bv.index])<<bv.bitCap
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}
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// Here be dragons
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inc := (bv.bitCap - 8) >> 7 // inc == 1 iff bitcap<8 (+10% perf)
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bv.index = bv.index + int(inc)
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bv.bitCap = bv.bitCap + inc<<3
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return res
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}
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func writeBitvec(buf []byte) *wbitvec {
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return &wbitvec{buf: buf[:0]}
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}
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type wbitvec struct {
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buf []byte
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index int
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bits uint16
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bitCap byte
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}
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func (bv *wbitvec) Out() []byte {
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if bv.bitCap != 0 {
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bv.buf = append(bv.buf, 0)[:bv.index+1]
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bv.buf[bv.index] = byte(bv.bits)
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}
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if bv.bitCap > 8 {
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bv.buf = append(bv.buf, byte(bv.bitCap>>8))
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}
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return bv.buf
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}
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func (bv *wbitvec) Put(val byte, count byte) {
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bv.bits = bv.bits | uint16(val)<<bv.bitCap
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bv.bitCap = bv.bitCap + count
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bv.buf = append(bv.buf, 0)[:bv.index+1] // increase cap, keep len
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bv.buf[bv.index] = byte(bv.bits)
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// Warning, dragons again
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inc := (^(bv.bitCap - 8)) >> 7 // inc == 1 iff bitcap>=8
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bv.index = bv.index + int(inc)
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bv.bitCap = bv.bitCap - inc<<3
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bv.bits = bv.bits >> (inc << 3)
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}
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