1/*---------------------------------------------------------------------------*
2 *  filter.h  *
3 *                                                                           *
4 *  Copyright 2007, 2008 Nuance Communciations, Inc.                               *
5 *                                                                           *
6 *  Licensed under the Apache License, Version 2.0 (the 'License');          *
7 *  you may not use this file except in compliance with the License.         *
8 *                                                                           *
9 *  You may obtain a copy of the License at                                  *
10 *      http://www.apache.org/licenses/LICENSE-2.0                           *
11 *                                                                           *
12 *  Unless required by applicable law or agreed to in writing, software      *
13 *  distributed under the License is distributed on an 'AS IS' BASIS,        *
14 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. *
15 *  See the License for the specific language governing permissions and      *
16 *  limitations under the License.                                           *
17 *                                                                           *
18 *---------------------------------------------------------------------------*/
19
20#ifndef __FILTER_H__
21#define __FILTER_H__
22
23// Define new data types
24
25typedef short typeSample;  // for input and output samples
26typedef short typeCoeff;   // FIR filter coefficients
27typedef long  typeAccum;   // FIR filter accumulator
28
29#define FACTOR_UP                       1     // upsampling factor
30#define FACTOR_DOWN                     4     // downsampling factor
31
32#define u16ScaleFilterCoeff_up1_down4  15
33
34typedef struct fir_struct
35{
36   int              state;   // state of FIR delay line (index of next slot to fill)
37   typeSample      *z;       // pointer to delay line
38
39   unsigned int     factor_up;
40   unsigned int     factor_down;
41
42   unsigned int     nTaps;   // length of FIR filter
43   unsigned int     scale;   // fixed-point filter scale factor
44   const typeCoeff *h;       // pointer to FIR filter coefficients
45   typeAccum        round;   // used for roundoff
46} FIR_struct;
47
48extern const typeCoeff ps16FilterCoeff_up1_down4[];
49
50extern unsigned int filter_length;
51
52extern  void FIR_downsample(unsigned int nInput, typeSample *pInput,
53			   typeSample *pOutput, FIR_struct *pFIR);
54
55extern  FIR_struct* FIR_construct(unsigned int nTaps, const typeCoeff *pCoeffs, int scale, int factor_up, int factor_down);
56
57extern  int FIR_deconstruct(FIR_struct *pFIR);
58
59extern  void FIR_reset(FIR_struct *pFIR);
60
61#endif
62