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/*
** Copyright 2003-2010, VisualOn, Inc.
**
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
**
** http://www.apache.org/licenses/LICENSE-2.0
**
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*/
/***********************************************************************
* File: lp_dec2.c *
* *
* Description:Decimate a vector by 2 with 2nd order fir filter *
* *
************************************************************************/
#include "typedef.h"
#include "basic_op.h"
#include "cnst.h"
#define L_FIR 5
#define L_MEM (L_FIR-2)
/* static float h_fir[L_FIR] = {0.13, 0.23, 0.28, 0.23, 0.13}; */
/* fixed-point: sum of coef = 32767 to avoid overflow on DC */
static Word16 h_fir[L_FIR] = {4260, 7536, 9175, 7536, 4260};
void LP_Decim2(
Word16 x[], /* in/out: signal to process */
Word16 l, /* input : size of filtering */
Word16 mem[] /* in/out: memory (size=3) */
)
{
Word16 *p_x, x_buf[L_FRAME + L_MEM];
Word32 i, j;
Word32 L_tmp;
/* copy initial filter states into buffer */
p_x = x_buf;
for (i = 0; i < L_MEM; i++)
{
*p_x++ = mem[i];
mem[i] = x[l - L_MEM + i];
}
for (i = 0; i < l; i++)
{
*p_x++ = x[i];
}
for (i = 0, j = 0; i < l; i += 2, j++)
{
p_x = &x_buf[i];
L_tmp = ((*p_x++) * h_fir[0]);
L_tmp += ((*p_x++) * h_fir[1]);
L_tmp += ((*p_x++) * h_fir[2]);
L_tmp += ((*p_x++) * h_fir[3]);
L_tmp += ((*p_x++) * h_fir[4]);
x[j] = (L_tmp + 0x4000)>>15;
}
return;
}
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