/* | |
** 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; | |
} | |