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diff --git a/subversion/libsvn_fs_x/changes.h b/subversion/libsvn_fs_x/changes.h
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+/* changes.h --- FSX changed paths lists container
+ *
+ * ====================================================================
+ *    Licensed to the Apache Software Foundation (ASF) under one
+ *    or more contributor license agreements.  See the NOTICE file
+ *    distributed with this work for additional information
+ *    regarding copyright ownership.  The ASF licenses this file
+ *    to you under the Apache License, Version 2.0 (the
+ *    "License"); you may not use this file except in compliance
+ *    with the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing,
+ *    software distributed under the License is distributed on an
+ *    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *    KIND, either express or implied.  See the License for the
+ *    specific language governing permissions and limitations
+ *    under the License.
+ * ====================================================================
+ */
+
+#ifndef SVN_LIBSVN_FS__CHANGES_H
+#define SVN_LIBSVN_FS__CHANGES_H
+
+#include "svn_io.h"
+#include "fs.h"
+
+/* Entries in a revision's change list tend to be widely redundant (similar
+ * changes to similar paths).  Even more so, change lists from a larger
+ * revision range also tend to overlap.
+ *
+ * In its serialized form, the svn_fs_x__changes_t container extracts most
+ * of that redundancy and the run-time representation is also much smaller
+ * than sum of the respective svn_fs_x__change_t* arrays.
+ *
+ * As with other containers, this one has two modes: 'construction', in
+ * which you may add data to it, and 'getter' in which there is only r/o
+ * access to the data.
+ */
+
+/* An opaque collection of change lists (apr_array_header_t * of
+ * svn_fs_x__change_t *).
+ */
+typedef struct svn_fs_x__changes_t svn_fs_x__changes_t;
+
+/* Create and populate changes containers. */
+
+/* Create and return a new changes container with an initial capacity of
+ * INITIAL_COUNT svn_fs_x__change_t objects.
+ * Allocate the result in RESULT_POOL.
+ */
+svn_fs_x__changes_t *
+svn_fs_x__changes_create(apr_size_t initial_count,
+                         apr_pool_t *result_pool);
+
+/* Start a new change list CHANGES (implicitly terminating the previous one)
+ * and return its index in *LIST_INDEX.  Append all changes from LIST to
+ * that new change list.
+ */
+svn_error_t *
+svn_fs_x__changes_append_list(apr_size_t *list_index,
+                              svn_fs_x__changes_t *changes,
+                              apr_array_header_t *list);
+
+/* Return a rough estimate in bytes for the serialized representation
+ * of CHANGES.
+ */
+apr_size_t
+svn_fs_x__changes_estimate_size(const svn_fs_x__changes_t *changes);
+
+/* Read changes containers. */
+
+/* From CHANGES, extract the change list with the given IDX.  Allocate
+ * the result in POOL and return it in *LIST.
+ */
+svn_error_t *
+svn_fs_x__changes_get_list(apr_array_header_t **list,
+                           const svn_fs_x__changes_t *changes,
+                           apr_size_t idx,
+                           apr_pool_t *pool);
+
+/* I/O interface. */
+
+/* Write a serialized representation of CHANGES to STREAM.
+ * Use SCRATCH_POOL for temporary allocations.
+ */
+svn_error_t *
+svn_fs_x__write_changes_container(svn_stream_t *stream,
+                                  const svn_fs_x__changes_t *changes,
+                                  apr_pool_t *scratch_pool);
+
+/* Read a changes container from its serialized representation in STREAM.
+ * Allocate the result in RESULT_POOL and return it in *CHANGES_P.  Use
+ * SCRATCH_POOL for temporary allocations.
+ */
+svn_error_t *
+svn_fs_x__read_changes_container(svn_fs_x__changes_t **changes_p,
+                                 svn_stream_t *stream,
+                                 apr_pool_t *result_pool,
+                                 apr_pool_t *scratch_pool);
+
+/* Implements #svn_cache__serialize_func_t for svn_fs_x__changes_t objects.
+ */
+svn_error_t *
+svn_fs_x__serialize_changes_container(void **data,
+                                      apr_size_t *data_len,
+                                      void *in,
+                                      apr_pool_t *pool);
+
+/* Implements #svn_cache__deserialize_func_t for svn_fs_x__changes_t objects.
+ */
+svn_error_t *
+svn_fs_x__deserialize_changes_container(void **out,
+                                        void *data,
+                                        apr_size_t data_len,
+                                        apr_pool_t *pool);
+
+/* Implements svn_cache__partial_getter_func_t for svn_fs_x__changes_t,
+ * setting *OUT to the change list (apr_array_header_t *) selected by
+ * the apr_uint32_t index passed in as *BATON.  This function is similar
+ * to svn_fs_x__changes_get_list but operates on the cache serialized
+ * representation of the container.
+ */
+svn_error_t *
+svn_fs_x__changes_get_list_func(void **out,
+                                const void *data,
+                                apr_size_t data_len,
+                                void *baton,
+                                apr_pool_t *pool);
+
+#endif