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diff --git a/audio/filter/filter.h b/audio/filter/filter.h
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+/*
+ * Copyright (C) 2001 Anders Johansson ajh@atri.curtin.edu.au
+ *
+ * This file is part of MPlayer.
+ *
+ * MPlayer is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * MPlayer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with MPlayer; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#if !defined MPLAYER_DSP_H
+# error Never use filter.h directly; include dsp.h instead.
+#endif
+
+#ifndef MPLAYER_FILTER_H
+#define MPLAYER_FILTER_H
+
+
+// Design and implementation of different types of digital filters
+
+
+// Flags used for filter design
+
+// Filter characteristics
+#define LP 0x00010000 // Low pass
+#define HP 0x00020000 // High pass
+#define BP 0x00040000 // Band pass
+#define BS 0x00080000 // Band stop
+#define TYPE_MASK 0x000F0000
+
+// Window types
+#define BOXCAR 0x00000001
+#define TRIANG 0x00000002
+#define HAMMING 0x00000004
+#define HANNING 0x00000008
+#define BLACKMAN 0x00000010
+#define FLATTOP 0x00000011
+#define KAISER 0x00000012
+#define WINDOW_MASK 0x0000001F
+
+// Parallel filter design
+#define FWD 0x00000001 // Forward indexing of polyphase filter
+#define REW 0x00000002 // Reverse indexing of polyphase filter
+#define ODD 0x00000010 // Make filter HP
+
+// Exported functions
+FLOAT_TYPE af_filter_fir(unsigned int n, const FLOAT_TYPE* w, const FLOAT_TYPE* x);
+
+int af_filter_design_fir(unsigned int n, FLOAT_TYPE* w, const FLOAT_TYPE* fc,
+ unsigned int flags, FLOAT_TYPE opt);
+
+int af_filter_szxform(const FLOAT_TYPE* a, const FLOAT_TYPE* b, FLOAT_TYPE Q,
+ FLOAT_TYPE fc, FLOAT_TYPE fs, FLOAT_TYPE *k,
+ FLOAT_TYPE *coef);
+
+/* Add new data to circular queue designed to be used with a FIR
+ filter. xq is the circular queue, in pointing at the new sample, xi
+ current index for xq and n the length of the filter. xq must be n*2
+ long.
+*/
+#define af_filter_updateq(n,xi,xq,in)\
+ xq[xi]=(xq)[(xi)+(n)]=*(in);\
+ xi=(++(xi))&((n)-1);
+
+#endif /* MPLAYER_FILTER_H */