[PATCH 1/5] Fix IPv6 zero-run compression.

[Owen Smith <owen.smith@xxxxxxxxxx>]

ZeroIndex was only set when the first zero was found, and ZeroCount is set to
the longest run of zeros. This would incorrectly compress an address with
a two runs of zeros, e.g. "1:0:0:2:0:0:0:3" to "1::0:0:0:3".
ZeroIndex should be recalculated whenever a longer run of zeros is detected,
so that the above run is correctly compressed to "1:0:2::3"

Simplifies the condition detecting an ending zero run, as Index would always
be 7 when a trailing ":" is required.

Assisted-by: ClaudeCode:claude-opus-4.8
Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>
---
 src/xenvif/frontend.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/src/xenvif/frontend.c b/src/xenvif/frontend.c
index bece661..56fcc30 100644
--- a/src/xenvif/frontend.c
+++ b/src/xenvif/frontend.c
@@ -774,22 +774,21 @@ FrontendDumpIPv6Address(
             Count = 0;
 
         if (Count > ZeroCount) {
-            if (Count == 1)
-                ZeroIndex = Index;
+            ZeroIndex = 1 + Index - Count;
             ZeroCount = Count;
         }
     }
 
     if (ZeroCount > 1) {
-        CHAR                        Parts[8][sizeof(":XXXX")];
+        CHAR                        Parts[8][sizeof(":XXXX")] = { 0 };
 
         for (Index = 0; Index < 8; Index++) {
             // Consecutive 0s are collapsed into a single semicolon, so that
             // appending :xxxx segments would work naturally.
             // Compensate for the missing appended semicolon if the last word
             // was also collapsed.
-            if (Index == ZeroIndex || (Index == 7 &&
-                                       Index == ZeroIndex + ZeroCount - 1)) {
+            if (Index == ZeroIndex ||
+                (Index == 7 && ZeroIndex + ZeroCount == 8)) {
                 Parts[Index][0] = ':';
                 Parts[Index][1] = '\0';
             } else if (Index > ZeroIndex && Index < ZeroIndex + ZeroCount) {
-- 
2.51.2.windows.1