Set p to its new offset before modifying it

redisbook · Aug 13, 2012 · 3cc2904 · 3cc2904
1 parent 5117c20
commit 3cc2904
Showing 1 changed file with 8 additions and 7 deletions.
diff --git a/src/ziplist.c b/src/ziplist.c
@@ -500,12 +500,13 @@ static unsigned char *__ziplistDelete(unsigned char *zl, unsigned char *p, unsig
     totlen = p-first.p;
     if (totlen > 0) {
         if (p[0] != ZIP_END) {
-            /* Tricky: storing the prevlen in this entry might reduce or
-             * increase the number of bytes needed, compared to the current
-             * prevlen. Note that we can always store this length because
-             * it was previously stored by an entry that is being deleted. */
+            /* Storing `prevrawlen` in this entry may increase or decrease the
+             * number of bytes required compare to the current `prevrawlen`.
+             * There always is room to store this, because it was previously
+             * stored by an entry that is now being deleted. */
             nextdiff = zipPrevLenByteDiff(p,first.prevrawlen);
-            zipPrevEncodeLength(p-nextdiff,first.prevrawlen);
+            p -= nextdiff;
+            zipPrevEncodeLength(p,first.prevrawlen);
 
             /* Update offset for tail */
             ZIPLIST_TAIL_OFFSET(zl) =
@@ -521,8 +522,8 @@ static unsigned char *__ziplistDelete(unsigned char *zl, unsigned char *p, unsig
             }
 
             /* Move tail to the front of the ziplist */
-            memmove(first.p,p-nextdiff,
-                intrev32ifbe(ZIPLIST_BYTES(zl))-(p-zl)-1+nextdiff);
+            memmove(first.p,p,
+                intrev32ifbe(ZIPLIST_BYTES(zl))-(p-zl)-1);
         } else {
             /* The entire tail was deleted. No need to move memory. */
             ZIPLIST_TAIL_OFFSET(zl) =