text_dct.c

来自「实现在linux下的mpeg4编解码」· C语言 代码 · 共 278 行

/**************************************************************************
 *                                                                        *
 * This code is developed by Adam Li.  This software is an                *
 * implementation of a part of one or more MPEG-4 Video tools as          *
 * specified in ISO/IEC 14496-2 standard.  Those intending to use this    *
 * software module in hardware or software products are advised that its  *
 * use may infringe existing patents or copyrights, and any such use      *
 * would be at such party's own risk.  The original developer of this     *
 * software module and his/her company, and subsequent editors and their  *
 * companies (including Project Mayo), will have no liability for use of  *
 * this software or modifications or derivatives thereof.                 *
 *                                                                        *
 * Project Mayo gives users of the Codec a license to this software       *
 * module or modifications thereof for use in hardware or software        *
 * products claiming conformance to the MPEG-4 Video Standard as          *
 * described in the Open DivX license.                                    *
 *                                                                        *
 * The complete Open DivX license can be found at                         *
 * http://www.projectmayo.com/opendivx/license.php .                      *
 *                                                                        *
 **************************************************************************/

/**************************************************************************
 *
 *  text_dct.c
 *
 *  Copyright (C) 2001  Project Mayo
 *
 *  Adam Li
 *
 *  DivX Advance Research Center <[e-mail]>
 *
 **************************************************************************/

/* This file contains some functions for fDCT/iDCT transformation.        */
/* Some codes of this project come from SSG MPEG-2 implementation.        */
/* Please see seperate acknowledgement file for a list of contributors.   */

#include <math.h>

/* The first part of it is for the forward DCT */

#ifndef PI
# ifdef M_PI
#  define PI M_PI
# else
#  define PI 3.14159265358979323846
# endif
#endif

/* private data */
static double c[8][8]; /* transform coefficients */

void fdct_enc(block)
short *block;
{
  int i, j, k;
  double s;
  double tmp[64];

  for (i=0; i<8; i++)
    for (j=0; j<8; j++)
    {
      s = 0.0;

      for (k=0; k<8; k++)
        s += c[j][k] * block[8*i+k];

      tmp[8*i+j] = s;
    }

  for (j=0; j<8; j++)
    for (i=0; i<8; i++)
    {
      s = 0.0;

      for (k=0; k<8; k++)
        s += c[i][k] * tmp[8*k+j];

      block[8*i+j] = (int)floor(s+0.499999);
      /*
       * reason for adding 0.499999 instead of 0.5:
       * s is quite often x.5 (at least for i and/or j = 0 or 4)
       * and setting the rounding threshold exactly to 0.5 leads to an
       * extremely high arithmetic implementation dependency of the result;
       * s being between x.5 and x.500001 (which is now incorrectly rounded
       * downwards instead of upwards) is assumed to occur less often
       * (if at all)
       */
    }
}

void init_fdct_enc()
{
  int i, j;
  double s;

  for (i=0; i<8; i++)
  {
    s = (i==0) ? sqrt(0.125) : 0.5;

    for (j=0; j<8; j++)
      c[i][j] = s * cos((PI/8.0)*i*(j+0.5));
  }
}




/* the second part of it is for the inverse DCT */

#define W1 2841 /* 2048*sqrt(2)*cos(1*pi/16) */
#define W2 2676 /* 2048*sqrt(2)*cos(2*pi/16) */
#define W3 2408 /* 2048*sqrt(2)*cos(3*pi/16) */
#define W5 1609 /* 2048*sqrt(2)*cos(5*pi/16) */
#define W6 1108 /* 2048*sqrt(2)*cos(6*pi/16) */
#define W7 565  /* 2048*sqrt(2)*cos(7*pi/16) */

/* private data */
static short iclip[1024]; /* clipping table */
static short *iclp;

/* private prototypes */
static void idctrow_enc (short *blk);
static void idctcol_enc (short *blk);

/* two dimensional inverse discrete cosine transform */
void idct_enc(block)
short *block;
{
  int i;

  for (i=0; i<8; i++)
    idctrow_enc(block+8*i);

  for (i=0; i<8; i++)
    idctcol_enc(block+i);
}

void init_idct_enc()
{
  int i;

  iclp = iclip+512;
  for (i= -512; i<512; i++)
    iclp[i] = (i<-256) ? -256 : ((i>255) ? 255 : i);
}

/* row (horizontal) IDCT
 *
 *           7                       pi         1
 * dst[k] = sum c[l] * src[l] * cos( -- * ( k + - ) * l )
 *          l=0                      8          2
 *
 * where: c[0]    = 128
 *        c[1..7] = 128*sqrt(2)
 */

static void idctrow_enc(blk)
short *blk;
{
  int x0, x1, x2, x3, x4, x5, x6, x7, x8;

  /* shortcut */
  if (!((x1 = blk[4]<<11) | (x2 = blk[6]) | (x3 = blk[2]) |
        (x4 = blk[1]) | (x5 = blk[7]) | (x6 = blk[5]) | (x7 = blk[3])))
  {
    blk[0]=blk[1]=blk[2]=blk[3]=blk[4]=blk[5]=blk[6]=blk[7]=blk[0]<<3;
    return;
  }

  x0 = (blk[0]<<11) + 128; /* for proper rounding in the fourth stage */

  /* first stage */
  x8 = W7*(x4+x5);
  x4 = x8 + (W1-W7)*x4;
  x5 = x8 - (W1+W7)*x5;
  x8 = W3*(x6+x7);
  x6 = x8 - (W3-W5)*x6;
  x7 = x8 - (W3+W5)*x7;
  
  /* second stage */
  x8 = x0 + x1;
  x0 -= x1;
  x1 = W6*(x3+x2);
  x2 = x1 - (W2+W6)*x2;
  x3 = x1 + (W2-W6)*x3;
  x1 = x4 + x6;
  x4 -= x6;
  x6 = x5 + x7;
  x5 -= x7;
  
  /* third stage */
  x7 = x8 + x3;
  x8 -= x3;
  x3 = x0 + x2;
  x0 -= x2;
  x2 = (181*(x4+x5)+128)>>8;
  x4 = (181*(x4-x5)+128)>>8;
  
  /* fourth stage */
  blk[0] = (x7+x1)>>8;
  blk[1] = (x3+x2)>>8;
  blk[2] = (x0+x4)>>8;
  blk[3] = (x8+x6)>>8;
  blk[4] = (x8-x6)>>8;
  blk[5] = (x0-x4)>>8;
  blk[6] = (x3-x2)>>8;
  blk[7] = (x7-x1)>>8;
}

/* column (vertical) IDCT
 *
 *             7                         pi         1
 * dst[8*k] = sum c[l] * src[8*l] * cos( -- * ( k + - ) * l )
 *            l=0                        8          2
 *
 * where: c[0]    = 1/1024
 *        c[1..7] = (1/1024)*sqrt(2)
 */
static void idctcol_enc(blk)
short *blk;
{
  int x0, x1, x2, x3, x4, x5, x6, x7, x8;

  /* shortcut */
  if (!((x1 = (blk[8*4]<<8)) | (x2 = blk[8*6]) | (x3 = blk[8*2]) |
        (x4 = blk[8*1]) | (x5 = blk[8*7]) | (x6 = blk[8*5]) | (x7 = blk[8*3])))
  {
    blk[8*0]=blk[8*1]=blk[8*2]=blk[8*3]=blk[8*4]=blk[8*5]=blk[8*6]=blk[8*7]=
      iclp[(blk[8*0]+32)>>6];
    return;
  }

  x0 = (blk[8*0]<<8) + 8192;

  /* first stage */
  x8 = W7*(x4+x5) + 4;
  x4 = (x8+(W1-W7)*x4)>>3;
  x5 = (x8-(W1+W7)*x5)>>3;
  x8 = W3*(x6+x7) + 4;
  x6 = (x8-(W3-W5)*x6)>>3;
  x7 = (x8-(W3+W5)*x7)>>3;
  
  /* second stage */
  x8 = x0 + x1;
  x0 -= x1;
  x1 = W6*(x3+x2) + 4;
  x2 = (x1-(W2+W6)*x2)>>3;
  x3 = (x1+(W2-W6)*x3)>>3;
  x1 = x4 + x6;
  x4 -= x6;
  x6 = x5 + x7;
  x5 -= x7;
  
  /* third stage */
  x7 = x8 + x3;
  x8 -= x3;
  x3 = x0 + x2;
  x0 -= x2;
  x2 = (181*(x4+x5)+128)>>8;
  x4 = (181*(x4-x5)+128)>>8;
  
  /* fourth stage */
  blk[8*0] = iclp[(x7+x1)>>14];
  blk[8*1] = iclp[(x3+x2)>>14];
  blk[8*2] = iclp[(x0+x4)>>14];
  blk[8*3] = iclp[(x8+x6)>>14];
  blk[8*4] = iclp[(x8-x6)>>14];
  blk[8*5] = iclp[(x0-x4)>>14];
  blk[8*6] = iclp[(x3-x2)>>14];
  blk[8*7] = iclp[(x7-x1)>>14];
}