/* * madplay - MPEG audio decoder and player * Copyright (C) 2000-2004 Robert Leslie * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program 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 General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA * * $Id: resample.c,v 1.11 2004/01/23 09:41:32 rob Exp $ */#  define mad_f_mul(x, y)   ((x) * (y))# ifdef HAVE_CONFIG_H#  include "config.h"# endif# include "global.h"# include <string.h>//# include <mad.h># include "mad.h"# include "resample.h"# include "audio.h"/* * NAME:	resample_init() * DESCRIPTION:	initialize resampling state */int resample_init(struct resample_state *state,		  unsigned int oldrate, unsigned int newrate){  mad_fixed_t ratio;  if (newrate == 0)    return -1;  ratio = mad_f_div(oldrate, newrate);  if (ratio <= 0 || ratio > MAX_RESAMPLEFACTOR * MAD_F_ONE)    return -1;  state->ratio = ratio;  state->step = 0;  state->last = 0;  return 0;}/* * NAME:	resample_block() * DESCRIPTION:	algorithmically change the sampling rate of a PCM sample block */unsigned int resample_block(struct resample_state *state,			    unsigned int nsamples, mad_fixed_t const *old,			    mad_fixed_t *new){  mad_fixed_t const *end, *begin;  /*   * This resampling algorithm is based on a linear interpolation, which is   * not at all the best sounding but is relatively fast and efficient.   *   * A better algorithm would be one that implements a bandlimited   * interpolation.   */  if (state->ratio == MAD_F_ONE) {    memcpy(new, old, nsamples * sizeof(mad_fixed_t));    return nsamples;  }  end   = old + nsamples;  begin = new;  if (state->step < 0) {    state->step = mad_f_fracpart(-state->step);    while (state->step < MAD_F_ONE) {      *new++ = state->step ?	state->last + mad_f_mul(*old - state->last, state->step) : state->last;      state->step += state->ratio;      if (((state->step + 0x00000080L) & 0x0fffff00L) == 0)	state->step = (state->step + 0x00000080L) & ~0x0fffffffL;    }    state->step -= MAD_F_ONE;  }  while (end - old > 1 + mad_f_intpart(state->step)) {    old        += mad_f_intpart(state->step);    state->step = mad_f_fracpart(state->step);    *new++ = state->step ?      *old + mad_f_mul(old[1] - old[0], state->step) : *old;    state->step += state->ratio;    if (((state->step + 0x00000080L) & 0x0fffff00L) == 0)      state->step = (state->step + 0x00000080L) & ~0x0fffffffL;  }  if (end - old == 1 + mad_f_intpart(state->step)) {    state->last = end[-1];    state->step = -state->step;  }  else    state->step -= mad_f_fromint(end - old);  return new - begin;}