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