Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!decvax!mcnc!gatech!bloom-beacon!mit-eddie!killer!codas!flnexus!kimbal!rick
From: rick@kimbal.UUCP (Rick Kimball)
Newsgroups: comp.sys.mac.programmer
Subject: Re: compression algorithm used my MAC on macpaint documents
Message-ID: <686@kimbal.UUCP>
Date: 27 Feb 88 03:04:30 GMT
References: <oW96M2y00XoH8Qo0=9@andrew.cmu.edu>
Organization: Mac Source BBS, Altamonte Spgs, FL
Lines: 104
Summary: Here's an implementation.

In article <oW96M2y00XoH8Qo0=9@andrew.cmu.edu>, gs1g+@andrew.cmu.edu (Gregory Jacob Stein) writes:
> 
> There is a Tech Note which describes the packing algorithm used in PackBits.  
> Note, though, that Apple reserves the right to change this at any time.
> 
> 		Greg
 
Here's another kind of answer (the kind I like ...  show me 
the way ...  don't give me theory).  A while back I wrote a 
program that runs on my UNIX-PC.  It reads MacPaint files and 
displays them on the console.  

I had to write my own UnPackBits function for UNIX.
Here it is:

-------------- Snip Snip Snip -------------- 
/*
    Name: UnPackBits.c

    Synopsis: UnPackBits( char **src, **dst, short rowBytes );

    Description: See Apple Tech Notes:
                         #86: MacPaint Document Format
                        #171: PackBits Data Format

    This software is Copyright (c) 1987 by Rick Kimball.

    Permission is hereby granted to copy, reproduce, redistribute or
    otherwise use this software as long as: there is no monetary
    profit gained specifically from the use or reproduction or this
    software, it is not sold, rented, traded or otherwise marketed, and
    this copyright notice is included prominently in any copy
    made.

    The author make no claims as to the fitness or correctness of
    this software for any use whatsoever, and it is provided as is.
    Any use of this software is at the user's own risk.

    Sample Call Sequence:

    char **srcPtr, **dstPtr;
    char macPaintFile[(576/8)*720];
    char bitImage[51840];

    ...
    srcPtr = (char **)&macPaintFile[512];
    dstPtr = (char **)&bitImage[0];

    for( x = 0; x < 720; x++)
    {
        UnPackBits(&srcPtr,&dstPtr, 576/8);
    }
    ...


*/

#define HIGH_BIT_ON 0x80

UnPackBits(src, dst, cnt)
register unsigned char **src;
register unsigned char **dst;
register short cnt;
{
	register short noOfBytes;
	register unsigned char bit15;

	if ( cnt <= 0 )
		return(0);

	bit15 = HIGH_BIT_ON;

	while ( cnt )
	{
		if ( **src & bit15 )	/* Is High bit set ? */
		{
			noOfBytes = abs((char)*(*src)++);
			cnt -= ++noOfBytes;
			while( noOfBytes-- )
			{
				*(*dst)++ = **src;
			}
			(*src)++;
		}
		else	/* It is a normal zero based counter */
		{
			noOfBytes = (char)*(*src)++;
			cnt -= ++noOfBytes;
			while( noOfBytes-- )
			{
				*(*dst)++ = *(*src)++;
			}
		}
	}
	return(0);
}



-- 
Rick Kimball       Software Design Group
                   Maitland, FL 32751
                   (305) 660-0006
                   UUCP: rick@kimbal, ...codas!flnexus!kimbal!rick