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Clarify ESN bitmap length construction logic

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Signed-off-by: Alessandro Boch <aboch@tetrationanalytics.com>
This commit is contained in:
Alessandro Boch 2018-02-06 11:51:23 -08:00 committed by Alessandro Boch
parent a2af46a09c
commit d35d6b58e1
1 changed files with 4 additions and 2 deletions

6
xfrm_state_linux.go
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@ -69,8 +69,10 @@ func writeReplayEsn(replayWindow int) []byte {
ReplayWindow: uint32(replayWindow),
}
// taken from iproute2/ip/xfrm_state.c:
replayEsn.BmpLen = uint32((replayWindow + (4 * 8) - 1) / (4 * 8))
// Linux stores the bitmap to identify the already received sequence packets in blocks of uint32 elements.
// Therefore bitmap length is the minimum number of uint32 elements needed. The following is a ceiling operation.
bytesPerElem := int(unsafe.Sizeof(replayEsn.BmpLen)) // Any uint32 variable is good for this
replayEsn.BmpLen = uint32((replayWindow + (bytesPerElem * 8) - 1) / (bytesPerElem * 8))
return replayEsn.Serialize()
}