1 /*
2 ** Copyright 2003-2010, VisualOn, Inc.
3 **
4 ** Licensed under the Apache License, Version 2.0 (the "License");
5 ** you may not use this file except in compliance with the License.
6 ** You may obtain a copy of the License at
7 **
8 ** http://www.apache.org/licenses/LICENSE-2.0
9 **
10 ** Unless required by applicable law or agreed to in writing, software
11 ** distributed under the License is distributed on an "AS IS" BASIS,
12 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 ** See the License for the specific language governing permissions and
14 ** limitations under the License.
15 */
16
17 /***********************************************************************
18 * File: lp_dec2.c *
19 * *
20 * Description:Decimate a vector by 2 with 2nd order fir filter *
21 * *
22 ************************************************************************/
23
24 #include "typedef.h"
25 #include "basic_op.h"
26 #include "cnst.h"
27
28 #define L_FIR 5
29 #define L_MEM (L_FIR-2)
30
31 /* static float h_fir[L_FIR] = {0.13, 0.23, 0.28, 0.23, 0.13}; */
32 /* fixed-point: sum of coef = 32767 to avoid overflow on DC */
33 static Word16 h_fir[L_FIR] = {4260, 7536, 9175, 7536, 4260};
34
LP_Decim2(Word16 x[],Word16 l,Word16 mem[])35 void LP_Decim2(
36 Word16 x[], /* in/out: signal to process */
37 Word16 l, /* input : size of filtering */
38 Word16 mem[] /* in/out: memory (size=3) */
39 )
40 {
41 Word16 *p_x, x_buf[L_FRAME + L_MEM];
42 Word32 i, j;
43 Word32 L_tmp;
44 /* copy initial filter states into buffer */
45 p_x = x_buf;
46 for (i = 0; i < L_MEM; i++)
47 {
48 *p_x++ = mem[i];
49 mem[i] = x[l - L_MEM + i];
50 }
51 for (i = 0; i < l; i++)
52 {
53 *p_x++ = x[i];
54 }
55 for (i = 0, j = 0; i < l; i += 2, j++)
56 {
57 p_x = &x_buf[i];
58 L_tmp = ((*p_x++) * h_fir[0]);
59 L_tmp += ((*p_x++) * h_fir[1]);
60 L_tmp += ((*p_x++) * h_fir[2]);
61 L_tmp += ((*p_x++) * h_fir[3]);
62 L_tmp += ((*p_x++) * h_fir[4]);
63 x[j] = (L_tmp + 0x4000)>>15;
64 }
65 return;
66 }
67
68
69
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71