src/rate_half_fir.h

   1 /* Effect: change sample rate     Copyright (c) 2008 robs@users.sourceforge.net
   2  *
   3  * This library is free software; you can redistribute it and/or modify it
   4  * under the terms of the GNU Lesser General Public License as published by
   5  * the Free Software Foundation; either version 2.1 of the License, or (at
   6  * your option) any later version.
   7  *
   8  * This library is distributed in the hope that it will be useful, but
   9  * WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public License
  14  * along with this library; if not, write to the Free Software Foundation,
  15  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  16  */
  17
  18 /* Down-sample by a factor of 2 using a FIR with odd length (LEN).*/
  19 /* Input must be preceded and followed by LEN >> 1 samples. */
  20
  21 #define _ sum += (input[-j] + input[j]) * COEFS[j], ++j;
  22 static void FUNCTION(stage_t * p, fifo_t * output_fifo)
  23 {
  24   sample_t const * input = stage_read_p(p);
  25   int i, num_out = (stage_occupancy(p) + 1) / 2;
  26   sample_t * output = fifo_reserve(output_fifo, num_out);
  27
  28   for (i = 0; i < num_out; ++i, input += 2) {
  29     int j = 1;
  30     sample_t sum = input[0] * COEFS[0];
  31     CONVOLVE
  32     assert(j == array_length(COEFS));
  33     output[i] = sum;
  34   }
  35   fifo_read(&p->fifo, 2 * num_out, NULL);
  36 }
  37 #undef _
  38 #undef COEFS
  39 #undef CONVOLVE
  40 #undef FUNCTION