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00046 #include <stdio.h>
00047 #include <string.h>
00048
00049 #define SQ(x) ((x)*(x))
00050 #define ROUND_DIV(a,b) (((a) + ((b)/2))/(b))
00051
00052 #define NUM_TAPS 256
00053 #define BLOCK_SIZE 64
00054
00055 void echo_cancel(const short *out_buf, const short *in, size_t block_size, int *filter_q16, size_t num_taps, short *echo_cancelled_in)
00056 {
00057 const short *cur_out = &out_buf[block_size-1];
00058 const short *cur_in = &in[block_size-1];
00059 short *cur_in_ec = &echo_cancelled_in[block_size-1];
00060
00061 const short *out_p;
00062 int out_norm_sq_p16;
00063
00064
00065 out_norm_sq_p16 = 0;
00066 for (out_p = &out_buf[block_size+num_taps-1]; out_p != &out_buf[block_size-1]; --out_p)
00067 out_norm_sq_p16 += SQ(ROUND_DIV((int) *out_p, 1 << 8));
00068
00069 do
00070 {
00071 int *filter_q16_p;
00072 int echo_est_q16;
00073 short echo_est;
00074
00075
00076 echo_est_q16 = 0;
00077 for (out_p = &cur_out[num_taps-1], filter_q16_p = &filter_q16[num_taps-1]; out_p != cur_out; --out_p, --filter_q16_p)
00078 echo_est_q16 += (int) (*out_p)*(*filter_q16_p);
00079
00080 echo_est = ROUND_DIV(echo_est_q16, 1 << 16);
00081
00082
00083
00084
00085
00086
00087 *cur_in_ec = *cur_in - echo_est;
00088
00089
00090 out_norm_sq_p16 += SQ(ROUND_DIV((int) cur_out[0], 1<<8)) - SQ(ROUND_DIV((int) cur_out[num_taps], 1<<8));
00091
00092
00093 if (out_norm_sq_p16 != 0)
00094 {
00095 for (out_p = &cur_out[num_taps-1], filter_q16_p = &filter_q16[num_taps-1]; out_p != cur_out; --out_p, --filter_q16_p)
00096 *filter_q16_p += ROUND_DIV((int) *cur_in_ec * (int) *out_p, out_norm_sq_p16);
00097 }
00098 } while (cur_out--, cur_in_ec--, cur_in-- != in);
00099 }
00100
00101
00102 int main(int argc, char *_argv[])
00103 {
00104 short out_buf[BLOCK_SIZE+NUM_TAPS];
00105 int filter_q16[NUM_TAPS];
00106
00107 memset(out_buf, 0, sizeof (out_buf));
00108 memset(filter_q16, 0, sizeof (filter_q16));
00109
00110
00111 while (!kbhit())
00112 {
00113 short in[BLOCK_SIZE];
00114 short echo_cancelled_in[BLOCK_SIZE];
00115
00116
00117
00118 play_record_local(outBuf, in, BLOCK_SIZE);
00119
00120
00121
00122 echo_cancel(out_buf, in, BLOCK_SIZE, filter_q16, NUM_TAPS, echo_cancelled_in);
00123
00124
00125 memmove (& out_buf[BLOCK_SIZE], &out_buf[0], sizeof (out_buf) - sizeof (in));
00126
00127
00128 play_record_remote(echo_cancelled_in, out, BLOCK_SIZE);
00129 }
00130 }