--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.3/spandsp-0.0.3/src/spandsp/biquad.h	Fri Jun 25 16:00:21 2010 +0200
@@ -0,0 +1,116 @@
+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * biquad.h - General telephony bi-quad section routines (currently this just
+ *            handles canonic/type 2 form)
+ *
+ * Written by Steve Underwood <steveu@coppice.org>
+ *
+ * Copyright (C) 2001 Steve Underwood
+ *
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * $Id: biquad.h,v 1.9 2006/10/24 13:45:28 steveu Exp $
+ */
+
+/*! \page biquad_page Bi-quadratic filter sections
+\section biquad_page_sec_1 What does it do?
+???.
+
+\section biquad_page_sec_2 How does it work?
+???.
+*/
+
+#if !defined(_BIQUAD_H_)
+#define _BIQUAD_H_
+
+typedef struct
+{
+    int32_t gain;
+    int32_t a1;
+    int32_t a2;
+    int32_t b1;
+    int32_t b2;
+
+    int32_t z1;
+    int32_t z2;
+
+#if FIRST_ORDER_NOISE_SHAPING
+    int32_t residue;
+#elif SECOND_ORDER_NOISE_SHAPING
+    int32_t residue1;
+    int32_t residue2;
+#endif
+} biquad2_state_t;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+static __inline__ void biquad2_init(biquad2_state_t *bq,
+                                    int32_t gain,
+                                    int32_t a1,
+                                    int32_t a2,
+                                    int32_t b1,
+                                    int32_t b2)
+{
+    bq->gain = gain;
+    bq->a1 = a1;
+    bq->a2 = a2;
+    bq->b1 = b1;
+    bq->b2 = b2;
+    
+    bq->z1 = 0;
+    bq->z2 = 0;    
+
+#if FIRST_ORDER_NOISE_SHAPING
+    bq->residue = 0;
+#elif SECOND_ORDER_NOISE_SHAPING
+    bq->residue1 = 0;
+    bq->residue2 = 0;
+#endif
+}
+/*- End of function --------------------------------------------------------*/
+
+static __inline__ int16_t biquad2(biquad2_state_t *bq, int16_t sample)
+{
+    int32_t y;
+    int32_t z0;
+    
+    z0 = sample*bq->gain + bq->z1*bq->a1 + bq->z2*bq->a2;
+    y = z0 + bq->z1*bq->b1 + bq->z2*bq->b2;
+
+    bq->z2 = bq->z1;
+    bq->z1 = z0 >> 15;
+#if FIRST_ORDER_NOISE_SHAPING
+    y += bq->residue; 
+    bq->residue = y & 0x7FFF;
+#elif SECOND_ORDER_NOISE_SHAPING
+    y += (2*bq->residue1 - bq->residue2);
+    bq->residue2 = bq->residue1;
+    bq->residue1 = y & 0x7FFF;
+#endif
+    y >>= 15;
+    return (int16_t) y;
+}
+/*- End of function --------------------------------------------------------*/
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+/*- End of file ------------------------------------------------------------*/