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server/vendor/github.com/pion/interceptor/internal/sequencenumber/unwrapper.go

@@ -0,0 +1,45 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+// Package sequencenumber provides a sequence number unwrapper
+package sequencenumber
+
+const (
+	maxSequenceNumberPlusOne = int64(65536)
+	breakpoint               = 32768 // half of max uint16
+)
+
+// Unwrapper stores an unwrapped sequence number
+type Unwrapper struct {
+	init          bool
+	lastUnwrapped int64
+}
+
+func isNewer(value, previous uint16) bool {
+	if value-previous == breakpoint {
+		return value > previous
+	}
+	return value != previous && (value-previous) < breakpoint
+}
+
+// Unwrap unwraps the next sequencenumber
+func (u *Unwrapper) Unwrap(i uint16) int64 {
+	if !u.init {
+		u.init = true
+		u.lastUnwrapped = int64(i)
+		return u.lastUnwrapped
+	}
+
+	lastWrapped := uint16(u.lastUnwrapped)
+	delta := int64(i - lastWrapped)
+	if isNewer(i, lastWrapped) {
+		if delta < 0 {
+			delta += maxSequenceNumberPlusOne
+		}
+	} else if delta > 0 && u.lastUnwrapped+delta-maxSequenceNumberPlusOne >= 0 {
+		delta -= maxSequenceNumberPlusOne
+	}
+
+	u.lastUnwrapped += delta
+	return u.lastUnwrapped
+}