From: Gerrit Renker Date: Wed, 03 Jan 2007 13:08:07 +0000 Subject: [PATCH 2/5][REVISED]: Make dccp_delta_seqno return signed numbers Message-Id: <200701031308.07932@strip-the-willow> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: dccp@vger.kernel.org [DCCP]: Make dccp_delta_seqno return signed numbers Problem: -------- Using dccp_delta_seqno(a, b) produces unusable results when -- by accident or coincidence -- sequence number b precedes a. If e.g. a and b are merely reordered and have a distance 1, their delta_seqno is 2^48-1, which would indicate a loss of 2^48-2 packets. Fix: ---- The fix is by using signed 48-bit arithmetic for dccp_delta_seqno, so that dccp_delta_seqno(a, b) returns: * > 0 if a is `before' b OR * 0 if a = b OR * < 0 and > -2^47 if b is `before' a OR * -2^47 if neither a `before' b nor b `before' a This implements http://www.mail-archive.com/dccp@vger.kernel.org/msg01153.html Signed-off-by: Gerrit Renker Acked-by: Ian McDonald --- net/dccp/dccp.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/net/dccp/dccp.h +++ b/net/dccp/dccp.h @@ -113,9 +113,12 @@ static inline void dccp_inc_seqno(u64 *s *seqno = ADD48(*seqno, 1); } -static inline u64 dccp_delta_seqno(u64 seqno1, u64 seqno2) +/* return > 0 if seqno1 is `before' seqno2, <= 0 otherwise */ +static inline s64 dccp_delta_seqno(const u64 seqno1, const u64 seqno2) { - return ((seqno2 << 16) - (seqno1 << 16)) >> 16; + u64 delta = SUB48(seqno2, seqno1); + + return TO_SIGNED48(delta); } /* is seq1 < seq2 ? */