Add MDB_PREV_MULTIPLE

Logical counterpart to GET_MULTIPLE, NEXT_MULTIPLE

libraries/liblmdb/lmdb.h

@@ -392,7 +392,9 @@ typedef enum MDB_cursor_op {
 	MDB_PREV_NODUP,			/**< Position at last data item of previous key */
 	MDB_SET,				/**< Position at specified key */
 	MDB_SET_KEY,			/**< Position at specified key, return key + data */
-	MDB_SET_RANGE			/**< Position at first key greater than or equal to specified key. */
+	MDB_SET_RANGE,			/**< Position at first key greater than or equal to specified key. */
+	MDB_PREV_MULTIPLE		/**< Position at previous page and return key and up to
+								a page of duplicate data items. Only for #MDB_DUPFIXED */
 } MDB_cursor_op;
 
 /** @defgroup  errors	Return Codes

libraries/liblmdb/mdb.c

@@ -6997,6 +6997,28 @@ fetchm:
 			}
 		}
 		break;
+	case MDB_PREV_MULTIPLE:
+		if (data == NULL) {
+			rc = EINVAL;
+			break;
+		}
+		if (!(mc->mc_db->md_flags & MDB_DUPFIXED)) {
+			rc = MDB_INCOMPATIBLE;
+			break;
+		}
+		if (!(mc->mc_flags & C_INITIALIZED))
+			rc = mdb_cursor_first(mc, key, data);
+		else {
+			MDB_cursor *mx = &mc->mc_xcursor->mx_cursor;
+			if (mx->mc_flags & C_INITIALIZED) {
+				rc = mdb_cursor_sibling(mx, 0);
+				if (rc == MDB_SUCCESS)
+					goto fetchm;
+			} else {
+				rc = MDB_NOTFOUND;
+			}
+		}
+		break;
 	case MDB_NEXT:
 	case MDB_NEXT_DUP:
 	case MDB_NEXT_NODUP: