Initial commit

replay.go

@@ -0,0 +1,79 @@
+package lafsession
+
+type replayWindow struct {
+	maxSeq uint64
+	size   uint64
+	bits   []uint64
+}
+
+func newReplayWindow(size uint64) *replayWindow {
+	if size < 64 {
+		size = 64
+	}
+	words := (size + 63) / 64
+	return &replayWindow{
+		size: size,
+		bits: make([]uint64, words),
+	}
+}
+
+func (w *replayWindow) accept(seq uint64) bool {
+	if seq+w.size <= w.maxSeq {
+		return false
+	}
+	if seq > w.maxSeq {
+		shift := seq - w.maxSeq
+		if shift >= w.size {
+			for i := range w.bits {
+				w.bits[i] = 0
+			}
+		} else {
+			w.shift(shift)
+		}
+		w.maxSeq = seq
+	}
+	idx := w.maxSeq - seq
+	word := idx / 64
+	bit := idx % 64
+	if word >= uint64(len(w.bits)) {
+		return false
+	}
+	mask := uint64(1) << bit
+	if w.bits[word]&mask != 0 {
+		return false
+	}
+	w.bits[word] |= mask
+	return true
+}
+
+func (w *replayWindow) shift(n uint64) {
+	words := n / 64
+	bits := n % 64
+	if words > 0 {
+		copy(w.bits[words:], w.bits)
+		for i := uint64(0); i < words && i < uint64(len(w.bits)); i++ {
+			w.bits[i] = 0
+		}
+		for i := uint64(len(w.bits)); i > words; i-- {
+		}
+		if words < uint64(len(w.bits)) {
+			for i := 0; i < int(words); i++ {
+				w.bits[i] = 0
+			}
+		} else {
+			for i := range w.bits {
+				w.bits[i] = 0
+			}
+			return
+		}
+	}
+	if bits == 0 {
+		return
+	}
+	var carry uint64
+	for i := len(w.bits) - 1; i >= 0; i-- {
+		newCarry := w.bits[i] >> (64 - bits)
+		w.bits[i] = (w.bits[i] << bits) | carry
+		carry = newCarry
+	}
+}