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 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 70 71
