/* libSoX effect: Downsample * * First version of this effect written 11/2011 by Ulrich Klauer. * * Copyright 2011 Chris Bagwell and SoX Contributors * * This library is free software; you can redistribute it and/or modify it * under the terms of the GNU Lesser General Public License as published by * the Free Software Foundation; either version 2.1 of the License, or (at * your option) any later version. * * This library is distributed in the hope that it will be useful, but * WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser * General Public License for more details. * * You should have received a copy of the GNU Lesser General Public License * along with this library; if not, write to the Free Software Foundation, * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA */ #include "sox_i.h" typedef struct {  unsigned int factor;  unsigned int carry; /* number of samples still to be discarded,                         carried over from last block */} priv_t; static int soxcreate(sox_effect_t *effp, int argc, char **argv){  priv_t *p = (priv_t*)effp->priv;  p->factor = 2;  --argc, ++argv;  do { /* break-able block */    NUMERIC_PARAMETER(factor, 1, 16384)    USED(argv);  } while (0);  return argc ? lsx_usage(effp) : SOX_SUCCESS;} static int start(sox_effect_t *effp){  priv_t *p = (priv_t*) effp->priv;  effp->out_signal.rate = effp->in_signal.rate / p->factor;  return p->factor == 1 ? SOX_EFF_NULL : SOX_SUCCESS;} static int flow(sox_effect_t *effp, const sox_sample_t *ibuf,    sox_sample_t *obuf, size_t *isamp, size_t *osamp){  priv_t *p = (priv_t*)effp->priv;  size_t ilen = *isamp, olen = *osamp;  size_t t;   t = min(p->carry, ilen);  p->carry -= t;  ibuf += t; ilen -= t;   /* NB: either p->carry (usually) or ilen is now zero; hence, a     non-zero value of ilen implies p->carry == 0, and there is no     need to test for this in the following while and if. */   while (ilen >= p->factor && olen) {    *obuf++ = *ibuf;    ibuf += p->factor;    olen--; ilen -= p->factor;  }   if (ilen && olen) {    *obuf++ = *ibuf;    p->carry = p->factor - ilen;    olen--; ilen = 0;  }  USED(obuf);   *isamp -= ilen, *osamp -= olen;  return SOX_SUCCESS;} sox_effect_handler_t const *lsx_downsample_effect_fn(void){  static sox_effect_handler_t handler = {"downsample", "[factor (2)]",    SOX_EFF_RATE | SOX_EFF_MODIFY,    soxcreate, start, flow, NULL, NULL, NULL, sizeof(priv_t)};  return &handler;}