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diff --git a/compat/zlib/examples/zran.h b/compat/zlib/examples/zran.h
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+/* zran.h -- example of zlib/gzip stream indexing and random access
+ * Copyright (C) 2005, 2012, 2018 Mark Adler
+ * For conditions of distribution and use, see copyright notice in zlib.h
+ * Version 1.2  14 Oct 2018  Mark Adler */
+
+#include <stdio.h>
+#include "zlib.h"
+
+/* Access point list. */
+struct deflate_index {
+    int have;           /* number of list entries */
+    int gzip;           /* 1 if the index is of a gzip file, 0 if it is of a
+                           zlib stream */
+    off_t length;       /* total length of uncompressed data */
+    void *list;         /* allocated list of entries */
+};
+
+/* Make one entire pass through a zlib or gzip compressed stream and build an
+   index, with access points about every span bytes of uncompressed output.
+   gzip files with multiple members are indexed in their entirety. span should
+   be chosen to balance the speed of random access against the memory
+   requirements of the list, about 32K bytes per access point. The return value
+   is the number of access points on success (>= 1), Z_MEM_ERROR for out of
+   memory, Z_DATA_ERROR for an error in the input file, or Z_ERRNO for a file
+   read error. On success, *built points to the resulting index. */
+int deflate_index_build(FILE *in, off_t span, struct deflate_index **built);
+
+/* Deallocate an index built by deflate_index_build() */
+void deflate_index_free(struct deflate_index *index);
+
+/* Use the index to read len bytes from offset into buf. Return bytes read or
+   negative for error (Z_DATA_ERROR or Z_MEM_ERROR). If data is requested past
+   the end of the uncompressed data, then deflate_index_extract() will return a
+   value less than len, indicating how much was actually read into buf. This
+   function should not return a data error unless the file was modified since
+   the index was generated, since deflate_index_build() validated all of the
+   input. deflate_index_extract() will return Z_ERRNO if there is an error on
+   reading or seeking the input file. */
+int deflate_index_extract(FILE *in, struct deflate_index *index, off_t offset,
+                          unsigned char *buf, int len);