lp_dec2.c revision 41050cdb033641ddf26831d9272c0930f7b40a2d 
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 */
33static Word16 h_fir[L_FIR] = {4260, 7536, 9175, 7536, 4260};
34
35void 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}
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