window.c

这是一个和OGGPLAY的播放程序的附代码

/********************************************************************
 *                                                                  *
 * THIS FILE IS PART OF THE OggVorbis 'TREMOR' CODEC SOURCE CODE.   *
 *                                                                  *
 * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
 * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
 * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
 *                                                                  *
 * THE OggVorbis 'TREMOR' SOURCE CODE IS (C) COPYRIGHT 1994-2002    *
 * BY THE Xiph.Org FOUNDATION http://www.xiph.org/                  *
 *                                                                  *
 ********************************************************************

 function: window functions

 ********************************************************************/

#include <stdlib.h>
#include <math.h>
#include "os.h"
#include "misc.h"
#include "window.h"
#include "window_lookup.h"

const void *_vorbis_window(int type, int left){

  switch(type){
  case 0:

    switch(left){
    case 32:
      return vwin64;
    case 64:
      return vwin128;
    case 128:
      return vwin256;
    case 256:
      return vwin512;
    case 512:
      return vwin1024;
    case 1024:
      return vwin2048;
    case 2048:
      return vwin4096;
    case 4096:
      return vwin8192;
    default:
      return(0);
    }
    break;
  default:
    return(0);
  }
}

void _vorbis_apply_window(ogg_int32_t *d,const void *window_p[2],
			  long *blocksizes,
			  int lW,int W,int nW){
  
  LOOKUP_T *window[2];
  long n=blocksizes[W];
  long ln=blocksizes[lW];
  long rn=blocksizes[nW];

  long leftbegin=n/4-ln/4;
  long leftend=leftbegin+ln/2;

  long rightbegin=n/2+n/4-rn/4;
  long rightend=rightbegin+rn/2;
  
  int i,p;

  window[0]=window_p[0];
  window[1]=window_p[1];
  
  for(i=0;i<leftbegin;i++)
    d[i]=0;

  for(p=0;i<leftend;i++,p++)
    d[i]=MULT31(d[i],window[lW][p]);

  for(i=rightbegin,p=rn/2-1;i<rightend;i++,p--)
    d[i]=MULT31(d[i],window[nW][p]);

  for(;i<n;i++)
    d[i]=0;
}