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diff --git a/subversion/libsvn_fs_base/key-gen.h b/subversion/libsvn_fs_base/key-gen.h
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+++ b/subversion/libsvn_fs_base/key-gen.h
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+/* key-gen.c --- manufacturing sequential keys for some db tables
+ *
+ * ====================================================================
+ *    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_KEY_GEN_H
+#define SVN_LIBSVN_FS_KEY_GEN_H
+
+#include <apr.h>
+
+#include "svn_types.h"
+#include "private/svn_skel.h"  /* ### for svn_fs_base__{get,put}size() */
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+
+/* The alphanumeric keys passed in and out of svn_fs_base__next_key
+   are guaranteed never to be longer than this many bytes,
+   *including* the trailing null byte.  It is therefore safe
+   to declare a key as "char key[MAX_KEY_SIZE]".
+
+   Note that this limit will be a problem if the number of
+   keys in a table ever exceeds
+
+       18217977168218728251394687124089371267338971528174
+       76066745969754933395997209053270030282678007662838
+       67331479599455916367452421574456059646801054954062
+       15017704234999886990788594743994796171248406730973
+       80736524850563115569208508785942830080999927310762
+       50733948404739350551934565743979678824151197232629
+       947748581376,
+
+   but that's a risk we'll live with for now. */
+#define MAX_KEY_SIZE 200
+
+/* In many of the databases, the value at this key is the key to use
+   when storing a new record. */
+#define NEXT_KEY_KEY "next-key"
+
+
+/* Generate the next key after a given alphanumeric key.
+ *
+ * The first *LEN bytes of THIS are an ascii representation of a
+ * number in base 36: digits 0-9 have their usual values, and a-z have
+ * values 10-35.
+ *
+ * The new key is stored in NEXT, null-terminated.  NEXT must be at
+ * least *LEN + 2 bytes long -- one extra byte to hold a possible
+ * overflow column, and one for null termination.  On return, *LEN
+ * will be set to the length of the new key, not counting the null
+ * terminator.  In other words, the outgoing *LEN will be either equal
+ * to the incoming, or to the incoming + 1.
+ *
+ * If THIS contains anything other than digits and lower-case
+ * alphabetic characters, or if it starts with `0' but is not the
+ * string "0", then *LEN is set to zero and the effect on NEXT
+ * is undefined.
+ */
+void svn_fs_base__next_key(const char *this, apr_size_t *len, char *next);
+
+
+/* Compare two strings A and B as base-36 alphanumeric keys.
+ *
+ * Return -1, 0, or 1 if A is less than, equal to, or greater than B,
+ * respectively.
+ */
+int svn_fs_base__key_compare(const char *a, const char *b);
+
+/* Compare two strings A and B as base-36 alphanumber keys.
+ *
+ * Return TRUE iff both keys are NULL or both keys have the same
+ * contents.
+ */
+svn_boolean_t svn_fs_base__same_keys(const char *a, const char *b);
+
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* SVN_LIBSVN_FS_KEY_GEN_H */