idct.c

这是一个压缩解压包,用C语言进行编程的,里面有详细的源代码.

/*****************************************************************************
 *
 *  XVID MPEG-4 VIDEO CODEC
 *  - Inverse DCT  -
 *
 *  These routines are from Independent JPEG Group's free JPEG software
 *  Copyright (C) 1991-1998, Thomas G. Lane (see the file README.IJG)
 *
 *  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: idct.c,v 1.9 2005/11/22 10:23:01 suxen_drol Exp $
 *
 ****************************************************************************/

/* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */

/*
 * Disclaimer of Warranty
 *
 * These software programs are available to the user without any license fee or
 * royalty on an "as is" basis.  The MPEG Software Simulation Group disclaims
 * any and all warranties, whether express, implied, or statuary, including any
 * implied warranties or merchantability or of fitness for a particular
 * purpose.  In no event shall the copyright-holder be liable for any
 * incidental, punitive, or consequential damages of any kind whatsoever
 * arising from the use of these programs.
 *
 * This disclaimer of warranty extends to the user of these programs and user's
 * customers, employees, agents, transferees, successors, and assigns.
 *
 * The MPEG Software Simulation Group does not represent or warrant that the
 * programs furnished hereunder are free of infringement of any third-party
 * patents.
 *
 * Commercial implementations of MPEG-1 and MPEG-2 video, including shareware,
 * are subject to royalty fees to patent holders.  Many of these patents are
 * general enough such that they are unavoidable regardless of implementation
 * design.
 *
 * MPEG2AVI
 * --------
 * v0.16B33 renamed the initialization function to init_idct_int32()
 * v0.16B32 removed the unused idct_row() and idct_col() functions
 * v0.16B3  changed var declarations to static, to enforce data align
 * v0.16B22  idct_FAST() renamed to idct_int32()
 *        also merged idct_FAST() into a single function, to help VC++
 *        optimize it.
 *
 * v0.14  changed int to long, to avoid confusion when compiling on x86
 *        platform ( in VC++ "int" -> 32bits )
 */

/**********************************************************/
/* inverse two dimensional DCT, Chen-Wang algorithm       */
/* (cf. IEEE ASSP-32, pp. 803-816, Aug. 1984)             */
/* 32-bit integer arithmetic (8 bit coefficients)         */
/* 11 mults, 29 adds per DCT                              */
/*                                      sE, 18.8.91       */
/**********************************************************/
/* coefficients extended to 12 bit for IEEE1180-1990      */
/* compliance                           sE,  2.1.94       */
/**********************************************************/

/* this code assumes >> to be a two's-complement arithmetic */
/* right shift: (-2)>>1 == -1 , (-3)>>1 == -2               */

#include "idct.h"

#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
 * Initialized by idct_int32_init so it's mostly RO data,
 * doesn't hurt thread safety */
static short iclip[1024];		/* clipping table */
static short *iclp;

/* private prototypes */

/* 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)
 */

#if 0
static void idctrow(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;
}
#endif

/* 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)
 */

#if 0
static void idctcol(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];
}
#endif

/* function pointer */
idctFuncPtr idct;

/* two dimensional inverse discrete cosine transform */
void
idct_int32(short *const block)
{

	/*
	 * idct_int32_init() must be called before the first call to this
	 * function!
	 */


#if 0
	int i;
	long i;

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

	for (i=0; i<8; i++)
		idctcol(block+i);
#endif

	short *blk;
	long i;
	long X0, X1, X2, X3, X4, X5, X6, X7, X8;


	for (i = 0; i < 8; i++)		/* idct rows */
	{
		blk = block + (i << 3);
		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;
			continue;
		}

		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] = (short) ((X7 + X1) >> 8);
		blk[1] = (short) ((X3 + X2) >> 8);
		blk[2] = (short) ((X0 + X4) >> 8);
		blk[3] = (short) ((X8 + X6) >> 8);
		blk[4] = (short) ((X8 - X6) >> 8);
		blk[5] = (short) ((X0 - X4) >> 8);
		blk[6] = (short) ((X3 - X2) >> 8);
		blk[7] = (short) ((X7 - X1) >> 8);

	}							/* end for ( i = 0; i < 8; ++i ) IDCT-rows */



	for (i = 0; i < 8; i++)		/* idct columns */
	{
		blk = block + i;
		/* 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];
			continue;
		}

		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];
	}

}								/* end function idct_int32(block) */


void
idct_int32_init(void)
{
	int i;

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