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package main
/* Copyright (C) 2015-2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. */
/* Implementation of RFC6479
* https://tools.ietf.org/html/rfc6479
*
* The implementation is not safe for concurrent use!
*/
const (
// See: https://golang.org/src/math/big/arith.go
_Wordm = ^uintptr(0)
_WordLogSize = _Wordm>>8&1 + _Wordm>>16&1 + _Wordm>>32&1
_WordSize = 1 << _WordLogSize
)
const (
CounterRedundantBitsLog = _WordLogSize + 3
CounterRedundantBits = _WordSize * 8
CounterBitsTotal = 2048
CounterWindowSize = uint64(CounterBitsTotal - CounterRedundantBits)
)
const (
BacktrackWords = CounterBitsTotal / _WordSize
)
type ReplayFilter struct {
counter uint64
backtrack [BacktrackWords]uintptr
}
func (filter *ReplayFilter) Init() {
filter.counter = 0
filter.backtrack[0] = 0
}
func (filter *ReplayFilter) ValidateCounter(counter uint64) bool {
if counter >= RejectAfterMessages {
return false
}
indexWord := counter >> CounterRedundantBitsLog
if counter > filter.counter {
// move window forward
current := filter.counter >> CounterRedundantBitsLog
diff := minUint64(indexWord-current, BacktrackWords)
for i := uint64(1); i <= diff; i++ {
filter.backtrack[(current+i)%BacktrackWords] = 0
}
filter.counter = counter
} else if filter.counter-counter > CounterWindowSize {
// behind current window
return false
}
indexWord %= BacktrackWords
indexBit := counter & uint64(CounterRedundantBits-1)
// check and set bit
oldValue := filter.backtrack[indexWord]
newValue := oldValue | (1 << indexBit)
filter.backtrack[indexWord] = newValue
return oldValue != newValue
}
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