src/swap.c

   1 /* libSoX effect: swap pairs of audio channels
   2  *
   3  * First version written 01/2012 by Ulrich Klauer.
   4  * Replaces an older swap effect originally written by Chris Bagwell
   5  * on March 16, 1999.
   6  *
   7  * Copyright 2012 Chris Bagwell and SoX Contributors
   8  *
   9  * This library is free software; you can redistribute it and/or modify it
  10  * under the terms of the GNU Lesser General Public License as published by
  11  * the Free Software Foundation; either version 2.1 of the License, or (at
  12  * your option) any later version.
  13  *
  14  * This library is distributed in the hope that it will be useful, but
  15  * WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
  17  * General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public License
  20  * along with this library; if not, write to the Free Software Foundation,
  21  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  22  */
  23
  24 #include "sox_i.h"
  25
  26 static int start(sox_effect_t *effp)
  27 {
  28   return effp->in_signal.channels >= 2 ? SOX_SUCCESS : SOX_EFF_NULL;
  29 }
  30
  31 static int flow(sox_effect_t *effp, const sox_sample_t *ibuf,
  32     sox_sample_t *obuf, size_t *isamp, size_t *osamp)
  33 {
  34   size_t len = min(*isamp, *osamp);
  35   size_t channels = effp->in_signal.channels;
  36   len /= channels;
  37   *isamp = *osamp = len * channels;
  38
  39   while (len--) {
  40     size_t i;
  41     for (i = 0; i + 1 < channels; i += 2) {
  42       *obuf++ = ibuf[1];
  43       *obuf++ = ibuf[0];
  44       ibuf += 2;
  45     }
  46     if (channels % 2)
  47       *obuf++ = *ibuf++;
  48   }
  49
  50   return SOX_SUCCESS;
  51 }
  52
  53 sox_effect_handler_t const *lsx_swap_effect_fn(void)
  54 {
  55   static sox_effect_handler_t handler = {
  56     "swap", NULL,
  57     SOX_EFF_MCHAN | SOX_EFF_MODIFY,
  58     NULL, start, flow, NULL, NULL, NULL,
  59     0
  60   };
  61   return &handler;
  62 }