Subject: [PATH] [MCAST] IPv6: Fix algorithm to compute Querier's Query Interval and Maximum Response Delay

From: Yan Zheng <[email-masked]>
Date: Sat, 29 Oct 2005 00:02:32 +0800

5.1.3.  Maximum Response Code

   The Maximum Response Code field specifies the maximum time allowed
   before sending a responding Report.  The actual time allowed, called
   the Maximum Response Delay, is represented in units of milliseconds,
   and is derived from the Maximum Response Code as follows:

   If Maximum Response Code < 32768,
      Maximum Response Delay = Maximum Response Code

   If Maximum Response Code >=32768, Maximum Response Code represents a
   floating-point value as follows:

       0 1 2 3 4 5 6 7 8 9 A B C D E F
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |1| exp |          mant         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Maximum Response Delay = (mant | 0x1000) << (exp+3)

5.1.9.  QQIC (Querier's Query Interval Code)

   The Querier's Query Interval Code field specifies the [Query
   Interval] used by the Querier.  The actual interval, called the
   Querier's Query Interval (QQI), is represented in units of seconds,
   and is derived from the Querier's Query Interval Code as follows:

   If QQIC < 128, QQI = QQIC

   If QQIC >= 128, QQIC represents a floating-point value as follows:

       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      |1| exp | mant  |
      +-+-+-+-+-+-+-+-+

   QQI = (mant | 0x10) << (exp + 3)

                                                -- rfc3810

#define MLDV2_QQIC(value) MLDV2_EXP(0x80, 4, 3, value)
#define MLDV2_MRC(value) MLDV2_EXP(0x8000, 12, 3, value)

Above macro are defined in mcast.c. but 1 << 4 == 0x10 and 1 << 12 == 0x1000.
So the result computed by original Macro is larger.

Signed-off-by: Yan Zheng <[email-masked]>

Index: net/ipv6/mcast.c
===================================================================
--- linux-2.6.14/net/ipv6/mcast.c	2005-10-28 08:02:08.000000000 +0800
+++ linux/net/ipv6/mcast.c	2005-10-28 23:41:18.000000000 +0800
@@ -164,7 +164,7 @@
 #define MLDV2_MASK(value, nb) ((nb)>=32 ? (value) : ((1<<(nb))-1) & (value))
 #define MLDV2_EXP(thresh, nbmant, nbexp, value) \
 	((value) < (thresh) ? (value) : \
-	((MLDV2_MASK(value, nbmant) | (1<<(nbmant+nbexp))) << \
+	((MLDV2_MASK(value, nbmant) | (1<<(nbmant))) << \
 	(MLDV2_MASK((value) >> (nbmant), nbexp) + (nbexp))))
 
 #define MLDV2_QQIC(value) MLDV2_EXP(0x80, 4, 3, value)