predictor.h

很好的JPEG图象解码器,基于VC环境开发。

/*
 * predictor.h --
 * 
 * Code for predictor calculation. Its function version, predictor.c,
 * is used in debugging compilation.
 *
 * Copyright (c) 1994 Kongji Huang and Brian C. Smith.
 * Cornell University
 * All rights reserved.
 * 
 * Permission to use, copy, modify, and distribute this software and its
 * documentation for any purpose, without fee, and without written agreement is
 * hereby granted, provided that the above copyright notice and the following
 * two paragraphs appear in all copies of this software.
 * 
 * IN NO EVENT SHALL CORNELL UNIVERSITY BE LIABLE TO ANY PARTY FOR
 * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT
 * OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF CORNELL
 * UNIVERSITY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * 
 * CORNELL UNIVERSITY SPECIFICALLY DISCLAIMS ANY WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
 * ON AN "AS IS" BASIS, AND CORNELL UNIVERSITY HAS NO OBLIGATION TO
 * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 */

#ifndef _PREDICTOR
#define _PREDICTOR

#ifndef DEBUG

/*
 *--------------------------------------------------------------
 *
 * Predict --
 *
 *      Calculate the predictor for pixel[row][col][curComp],
 *	i.e. curRowBuf[col][curComp]. It handles the all special 
 *	cases at image edges, such as first row and first column
 *	of a scan.
 *
 * Results:
 *      predictor is passed out.
 *
 * Side effects:
 *      None.
 *
 *--------------------------------------------------------------
 */
#define Predict(row,col,curComp,curRowBuf,prevRowBuf,Pr,Pt,psv,predictor)\
{    register int left,upper,diag,leftcol;				\
									\
    leftcol=col-1;							\
    if (row==0) {							\
									\
       /*								\
        * The predictor of first pixel is (1<<(Pr-Pt-1), and the	\
        * predictors for rest of first row are left neighbors.		\
        */								\
       if (col==0) {							\
          *predictor = (1<<(Pr-Pt-1));					\
       }								\
       else {								\
          *predictor = curRowBuf[leftcol][curComp];			\
       }								\
    }									\
    else {								\
									\
       /*								\
        * The predictors of first column are upper neighbors.		\
        * All other preditors are calculated according to psv.		\
        */								\
       upper=prevRowBuf[col][curComp];					\
       if (col==0)							\
          *predictor = upper;						\
       else {								\
          left=curRowBuf[leftcol][curComp];				\
          diag=prevRowBuf[leftcol][curComp];				\
          switch (psv) {						\
             case 0:							\
                     *predictor = 0;					\
                     break;						\
             case 1:							\
                     *predictor = left;					\
                     break;						\
             case 2:							\
                     *predictor = upper;				\
                     break;						\
             case 3:							\
                     *predictor = diag;					\
                     break;						\
             case 4:							\
                     *predictor = left+upper-diag;			\
                     break;						\
             case 5:							\
                     *predictor = left+((upper-diag)>>1);		\
                     break;						\
             case 6:							\
                     *predictor = upper+((left-diag)>>1);		\
                     break;						\
             case 7:							\
                     *predictor = (left+upper)>>1;			\
                     break;						\
             default:							\
                     fprintf(stderr,"Warning: Undefined PSV\n");	\
                     *predictor = 0;					\
           }								\
        }								\
      }									\
}

/*
 *--------------------------------------------------------------
 *
 * QuickPredict --
 *
 *      Calculate the predictor for sample curRowBuf[col][curComp].
 *	It does not handle the special cases at image edges, such 
 *      as first row and first column of a scan. We put the special 
 *	case checkings outside so that the computations in main
 *	loop can be simpler. This has enhenced the performance
 *	significantly.
 *
 * Results:
 *      predictor is passed out.
 *
 * Side effects:
 *      None.
 *
 *--------------------------------------------------------------
 */
#define QuickPredict(col,curComp,curRowBuf,prevRowBuf,psv,predictor){	\
    register int left,upper,diag,leftcol;				\
									\
    leftcol=col-1;							\
    upper=prevRowBuf[col][curComp];					\
    left=curRowBuf[leftcol][curComp];					\
    diag=prevRowBuf[leftcol][curComp];					\
									\
    /* 									\
     * All predictor are calculated according to psv.			\
     */									\
    switch (psv) {							\
      case 0:								\
              *predictor = 0;						\
              break;							\
      case 1:								\
              *predictor = left;					\
              break;							\
      case 2:								\
              *predictor = upper;					\
              break;							\
      case 3:								\
              *predictor = diag;					\
              break;							\
      case 4:								\
              *predictor = left+upper-diag;				\
              break;							\
      case 5:								\
              *predictor = left+((upper-diag)>>1);			\
              break;							\
      case 6:								\
              *predictor = upper+((left-diag)>>1);			\
              break;							\
      case 7:								\
              *predictor = (left+upper)>>1;				\
              break;							\
      default:								\
              fprintf(stderr,"Warning: Undefined PSV\n");		\
              *predictor = 0;						\
     }									\
}

#endif /* DEBUG */
#endif /* _PREDICTOR */