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diff --git a/src/libmpg123/index.h b/src/libmpg123/index.h
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+#ifndef MPG123_H_INDEX
+#define MPG123_H_INDEX
+
+/*
+	index: frame index data structure and functions
+
+	This is for keeping track of frame positions for accurate seeking.
+	Now in it's own file, with initial code from frame.c and parse.c .
+
+	The idea of the index with a certain amount of entries is to cover
+	all yet-encountered frame positions with minimal coarseness.
+	Meaning: At first every frame position is recorded, then, when
+	the index is full, every second position is trown away to make
+	space. Next time it is full, the same happens. And so on.
+	In this manner we maintain a good resolution with the given
+	maximum index size while covering the whole stream.
+
+	copyright 2007-8 by the mpg123 project - free software under the terms of the LGPL 2.1
+	see COPYING and AUTHORS files in distribution or http://mpg123.org
+	initially written by Thomas Orgis
+*/
+
+#include "config.h"
+#include "compat.h"
+
+struct frame_index
+{
+	off_t *data; /* actual data, the frame positions */
+	off_t  step; /* advancement in frame number per index point */
+	off_t  next; /* frame offset supposed to come next into the index */
+	size_t size; /* total number of possible entries */
+	size_t fill; /* number of used entries */
+	size_t grow_size; /* if > 0: index allowed to grow on need with these steps, instead of lowering resolution */
+};
+
+/* The condition for a framenum to be appended to the index. 
+  if(FI_NEXT(fr->index, fr->num)) fi_add(offset); */
+#define FI_NEXT(fi, framenum) ((fi).size && framenum == (fi).next)
+
+/* Initialize stuff, set things to zero and NULL... */
+void fi_init(struct frame_index *fi);
+/* Deallocate/zero things. */
+void fi_exit(struct frame_index *fi);
+
+/* Prepare a given size, preserving current fill, if possible.
+   If the new size is smaller than fill, the entry density is reduced.
+   Return 0 on success. */
+int fi_resize(struct frame_index *fi, size_t newsize);
+
+/* Append a frame position, reducing index density if needed. */
+void fi_add(struct frame_index *fi, off_t pos);
+
+/* Empty the index (setting fill=0 and step=1), but keep current size. */
+void fi_reset(struct frame_index *fi);
+
+#endif