Merge 6d08c6a678 into b5a37c0e42

src/listpack.c

@@ -1456,6 +1456,45 @@ unsigned char *lpBatchDelete(unsigned char *lp, unsigned char **ps, unsigned lon
     return lpShrinkToFit(lp);
 }
 
+/* Trim a listpack, remove 'ltrim' elements from left and 'rtrim' elements from right. */
+unsigned char *lpTrim(unsigned char *lp, unsigned long ltrim, unsigned long rtrim) {
+    if (ltrim == 0 && rtrim == 0) return lp;
+    size_t bytes = lpBytes(lp);
+    unsigned long llen = lpLength(lp);
+    if (ltrim + rtrim >= llen) {
+        /* Remove all elements */
+        lp[LP_HDR_SIZE] = LP_EOF;
+        lpSetTotalBytes(lp, LP_HDR_SIZE + 1);
+        lpSetNumElements(lp, 0);
+        return lpShrinkToFit(lp);
+    }
+    unsigned long rangelen = llen - ltrim - rtrim;
+    unsigned char *first, *tail; /* first points to the first byte we want to save, 
+                                    and tail points to the byte after the last byte we want to save */
+    first = lpSeek(lp, ltrim);
+    assert(first != NULL);
+    tail = lp + bytes - 1; /* When rtrim is zero, tail points to the EOF char */
+    if (rtrim) {
+        if (rangelen < rtrim) {
+            tail = first;
+            unsigned long num = rangelen;
+            while (num--) {
+                tail = lpSkip(tail);
+            }
+            assert(tail[0] != LP_EOF);
+            lpAssertValidEntry(lp, bytes, tail);
+        } else {
+            tail = lpSeek(lp, llen - (int)rtrim);
+        }
+    }
+    size_t rangebytes = tail - first;
+    memmove(lp + LP_HDR_SIZE, first, rangebytes);
+    lp[LP_HDR_SIZE + rangebytes] = LP_EOF;
+    lpSetTotalBytes(lp, LP_HDR_SIZE + rangebytes + 1);
+    lpSetNumElements(lp, rangelen);
+    return lpShrinkToFit(lp);
+}
+
 /* Merge listpacks 'first' and 'second' by appending 'second' to 'first'.
  *
  * NOTE: The larger listpack is reallocated to contain the new merged listpack.

src/listpack.h

@@ -54,6 +54,7 @@ unsigned char *lpBatchAppend(unsigned char *lp, listpackEntry *entries, unsigned
 unsigned char *lpBatchInsert(unsigned char *lp, unsigned char *p, int where,
                              listpackEntry *entries, unsigned int len, unsigned char **newp);
 unsigned char *lpBatchDelete(unsigned char *lp, unsigned char **ps, unsigned long count);
+unsigned char *lpTrim(unsigned char *lp, unsigned long ltrim, unsigned long rtrim);
 unsigned char *lpMerge(unsigned char **first, unsigned char **second);
 unsigned char *lpDup(unsigned char *lp);
 unsigned long lpLength(unsigned char *lp);

src/t_list.c

@@ -961,8 +961,7 @@ void ltrimCommand(client *c) {
         quicklistDelRange(o->ptr,0,ltrim);
         quicklistDelRange(o->ptr,-rtrim,rtrim);
     } else if (o->encoding == OBJ_ENCODING_LISTPACK) {
-        o->ptr = lpDeleteRange(o->ptr,0,ltrim);
-        o->ptr = lpDeleteRange(o->ptr,-rtrim,rtrim);
+        o->ptr = lpTrim(o->ptr, ltrim, rtrim);
     } else {
         serverPanic("Unknown list encoding");
     }