ref: 0fa7b89f354773ce830f6bda12c8c27d2ad8b1d9
dir: /amr-wb/lp_dec2.c/
/*-------------------------------------------------------------------* * LP_DEC2.C * *-------------------------------------------------------------------* * Decimate a vector by 2 with 2nd order fir filter. * *-------------------------------------------------------------------*/ #include "typedef.h" #include "acelp.h" #include "basic_op.h" #include "count.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]; Word16 i, j, k; Word32 L_tmp; /* copy initial filter states into buffer */ p_x = x_buf; move16(); for (i = 0; i < L_MEM; i++) { *p_x++ = mem[i]; move16(); } for (i = 0; i < l; i++) { *p_x++ = x[i]; move16(); } for (i = 0; i < L_MEM; i++) { mem[i] = x[l - L_MEM + i]; move16(); } for (i = 0, j = 0; i < l; i += 2, j++) { p_x = &x_buf[i]; move16(); L_tmp = 0L; move32(); for (k = 0; k < L_FIR; k++) L_tmp = L_mac(L_tmp, *p_x++, h_fir[k]); x[j] = roundL(L_tmp); move16(); } return; }