Set p to its new offset before modifying it

1 files changed, 7 insertions, 6 deletions

diff --git a/src/ziplist.c b/src/ziplist.c
index 639e4b61e..9bc6d65d7 100644
--- a/src/ziplist.c
+++ b/src/ziplist.c
@@ -445,12 +445,13 @@ 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) -= totlen;
@@ -463,7 +464,7 @@ static unsigned char *__ziplistDelete(unsigned char *zl, unsigned char *p, unsig
                 ZIPLIST_TAIL_OFFSET(zl) += nextdiff;
 
             /* Move tail to the front of the ziplist */
-            memmove(first.p,p-nextdiff,ZIPLIST_BYTES(zl)-(p-zl)-1+nextdiff);
+            memmove(first.p,p,ZIPLIST_BYTES(zl)-(p-zl)-1);
         } else {
             /* The entire tail was deleted. No need to move memory. */
             ZIPLIST_TAIL_OFFSET(zl) = (first.p-zl)-first.prevrawlen;