Path: utzoo!attcan!utgpu!watmath!watdcsu!mgardi
From: mgardi@watdcsu.waterloo.edu (M.Gardi - ICR)
Newsgroups: comp.graphics
Subject: GIF Compression source - enjoy
Keywords: gif, lempel-ziv, compuserve
Message-ID: <5518@watdcsu.waterloo.edu>
Date: 9 Feb 89 23:30:20 GMT
Distribution: comp
Organization: U of Waterloo, Ontario
Lines: 749

Here is some source for GIF image compression.  It is set up for MSDOS,
but is trivial to modify for non-DOS machines (change the open for write
to "w" instead of "wb", remove the define for MSDOS, etc).

The source started out as the lempel-ziv 'compress' routine, and was modified
to output GIF files.

To use the GIFEncode function, define a function 'GetPixel' that
takes an X and Y co-ordinate (as int's) and returns the colour index
of that pixel.  Then call GIFEncode with the following:

	GIFEncode( Fname,          /* The filename to write */
	           GHeight,        /* The height of the bitmap - an int */
		   GWidth,         /* The width of the bitmap - an int */
		   GInterlace,     /* TRUE if you want the image to be
				      interlaced, FALSE otherwise */
	           Background,     /* The colour index of the background */
		   BitsPerPixel,   /* The number of bits of color per
				      pixel in the palette you specified.
				      If your palette has 256 colours,
				      it should be '8', 32 should be '5',
				      etc */
		   Red, Green, Blue, /* Pointers to arrays of int's,
					containing the R, G and B values
					of the colour palette */
	
		   GetPixel );	   /* a pointer to a function that returns
				      the index of the colour at the
				      co-ordinates passed */

----------cut here------------------cut here--------------------------------
#!/bin/sh
# This is a shell archive.  Remove anything before this line,
# then unpack it by saving it in a file and typing "sh file".
#
# Wrapped by watdcsu!mgardi on Thu Feb  9 18:19:39 EST 1989
# Contents:  gifcompr.c gifencod.c
 
echo x - gifcompr.c
sed 's/^@//' > "gifcompr.c" <<'@//E*O*F gifcompr.c//'
/***************************************************************************
 *
 *  GIFENCOD.C       - GIF Image compression routines
 *
 *  Lempel-Ziv compression based on 'compress'.  GIF modifications by
 *  David Rowley (mgardi@watdcsu.waterloo.edu)
 *
 ***************************************************************************/

/*
 * General DEFINEs
 */
#define min(a,b)        ((a>b) ? b : a)

#define BITS	12
#define MSDOS	1

#define HSIZE  5003            /* 80% occupancy */

/*
 * Pointer to function returning an int
 */
typedef int (* ifunptr)();

/*
 * a code_int must be able to hold 2**BITS values of type int, and also -1
 */
typedef int             code_int;

#ifdef SIGNED_COMPARE_SLOW
typedef unsigned long int count_int;
typedef unsigned short int count_short;
#else
typedef long int          count_int;
#endif

#ifdef NO_UCHAR
 typedef char   char_type;
#else
 typedef        unsigned char   char_type;
#endif /* UCHAR */

/*
 *
 * GIF Image compression - modified 'compress'
 *
 * Based on: compress.c - File compression ala IEEE Computer, June 1984.
 *
 * By Authors:  Spencer W. Thomas       (decvax!harpo!utah-cs!utah-gr!thomas)
 *              Jim McKie               (decvax!mcvax!jim)
 *              Steve Davies            (decvax!vax135!petsd!peora!srd)
 *              Ken Turkowski           (decvax!decwrl!turtlevax!ken)
 *              James A. Woods          (decvax!ihnp4!ames!jaw)
 *              Joe Orost               (decvax!vax135!petsd!joe)
 *
 */
#include <stdio.h>
#include <ctype.h>
#include <signal.h>

#define ARGVAL() (*++(*argv) || (--argc && *++argv))

static int n_bits;                        /* number of bits/code */
static int maxbits = BITS;                /* user settable max # bits/code */
static code_int maxcode;                  /* maximum code, given n_bits */
static code_int maxmaxcode = (code_int)1 << BITS; /* should NEVER generate this code */
#ifdef COMPATIBLE               /* But wrong! */
# define MAXCODE(n_bits)        ((code_int) 1 << (n_bits) - 1)
#else
# define MAXCODE(n_bits)        (((code_int) 1 << (n_bits)) - 1)
#endif /* COMPATIBLE */

static count_int htab [HSIZE];
static unsigned short codetab [HSIZE];
#define HashTabOf(i)       htab[i]
#define CodeTabOf(i)    codetab[i]

static code_int hsize = HSIZE;                 /* for dynamic table sizing */
static count_int fsize;

/*
 * To save much memory, we overlay the table used by compress() with those
 * used by decompress().  The tab_prefix table is the same size and type
 * as the codetab.  The tab_suffix table needs 2**BITS characters.  We
 * get this from the beginning of htab.  The output stack uses the rest
 * of htab, and contains characters.  There is plenty of room for any
 * possible stack (stack used to be 8000 characters).
 */

#define tab_prefixof(i) CodeTabOf(i)
#define tab_suffixof(i)        ((char_type *)(htab))[i]
#define de_stack               ((char_type *)&tab_suffixof((code_int)1<<BITS))

static code_int free_ent = 0;                  /* first unused entry */
static int exit_stat = 0;

/*
 * block compression parameters -- after all codes are used up,
 * and compression rate changes, start over.
 */
static int clear_flg = 0;

static int offset;
static long int in_count = 1;            /* length of input */
static long int out_count = 0;           /* # of codes output (for debugging) */

/*
 * compress stdin to stdout
 *
 * Algorithm:  use open addressing double hashing (no chaining) on the 
 * prefix code / next character combination.  We do a variant of Knuth's
 * algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
 * secondary probe.  Here, the modular division first probe is gives way
 * to a faster exclusive-or manipulation.  Also do block compression with
 * an adaptive reset, whereby the code table is cleared when the compression
 * ratio decreases, but after the table fills.  The variable-length output
 * codes are re-sized at this point, and a special CLEAR code is generated
 * for the decompressor.  Late addition:  construct the table according to
 * file size for noticeable speed improvement on small files.  Please direct
 * questions about this implementation to ames!jaw.
 */

static int g_init_bits;
static FILE *g_outfile;

static int ClearCode;
static int EOFCode;

compress( init_bits, outfile, ReadValue )
int init_bits;
FILE *outfile;
ifunptr ReadValue;
{
    register long fcode;
    register code_int i = 0;
    register int c;
    register code_int ent;
    register code_int disp;
    register code_int hsize_reg;
    register int hshift;

    /*
     * Set up the globals:  g_init_bits - initial number of bits
     *                      g_outfile   - pointer to output file
     */
    g_init_bits = init_bits;
    g_outfile = outfile;

    /*
     * Set up the necessary values
     */
    offset = 0;
    out_count = 0;
    clear_flg = 0;
    in_count = 1;
    maxcode = MAXCODE(n_bits = g_init_bits);

    ClearCode = (1 << (init_bits - 1));
    EOFCode = ClearCode + 1;
    free_ent = ClearCode + 2;

    char_init();
    
    ent = GIFNextPixel( ReadValue );

    hshift = 0;
    for ( fcode = (long) hsize;  fcode < 65536L; fcode *= 2L )
        hshift++;
    hshift = 8 - hshift;                /* set hash code range bound */

    hsize_reg = hsize;
    cl_hash( (count_int) hsize_reg);            /* clear hash table */

    output( (code_int)ClearCode );
    
#ifdef SIGNED_COMPARE_SLOW
    while ( (c = GIFNextPixel( ReadValue )) != (unsigned) EOF ) {
#else
    while ( (c = GIFNextPixel( ReadValue )) != EOF ) {
#endif

        in_count++;

        fcode = (long) (((long) c << maxbits) + ent);
        i = (((code_int)c << hshift) ^ ent);    /* xor hashing */

        if ( HashTabOf (i) == fcode ) {
            ent = CodeTabOf (i);
            continue;
        } else if ( (long)HashTabOf (i) < 0 )      /* empty slot */
            goto nomatch;
        disp = hsize_reg - i;           /* secondary hash (after G. Knott) */
        if ( i == 0 )
            disp = 1;
probe:
        if ( (i -= disp) < 0 )
            i += hsize_reg;

        if ( HashTabOf (i) == fcode ) {
            ent = CodeTabOf (i);
            continue;
        }
        if ( (long)HashTabOf (i) > 0 ) 
            goto probe;
nomatch:
        output ( (code_int) ent );
        out_count++;
        ent = c;
#ifdef SIGNED_COMPARE_SLOW
        if ( (unsigned) free_ent < (unsigned) maxmaxcode) {
#else
        if ( free_ent < maxmaxcode ) {
#endif
            CodeTabOf (i) = free_ent++; /* code -> hashtable */
            HashTabOf (i) = fcode;
        } else
		cl_block();
    }
    /*
     * Put out the final code.
     */
    output( (code_int)ent );
    out_count++;
    output( (code_int) EOFCode );

    return;
}

/*****************************************************************
 * TAG( output )
 *
 * Output the given code.
 * Inputs:
 *      code:   A n_bits-bit integer.  If == -1, then EOF.  This assumes
 *              that n_bits =< (long)wordsize - 1.
 * Outputs:
 *      Outputs code to the file.
 * Assumptions:
 *      Chars are 8 bits long.
 * Algorithm:
 *      Maintain a BITS character long buffer (so that 8 codes will
 * fit in it exactly).  Use the VAX insv instruction to insert each
 * code in turn.  When the buffer fills up empty it and start over.
 */

static unsigned long cur_accum = 0;
static int  cur_bits = 0;

static
unsigned long masks[] = { 0x0000, 0x0001, 0x0003, 0x0007, 0x000F,
                                  0x001F, 0x003F, 0x007F, 0x00FF,
                                  0x01FF, 0x03FF, 0x07FF, 0x0FFF,
                                  0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF };

static
output( code )
code_int  code;
{
    cur_accum &= masks[ cur_bits ];

    if( cur_bits > 0 )
    	cur_accum |= ((long)code << cur_bits);
    else
        cur_accum = code;
	
    cur_bits += n_bits;

    while( cur_bits >= 8 ) {
    	char_out( (unsigned int)(cur_accum & 0xff) );
	cur_accum >>= 8;
	cur_bits -= 8;
    }

    /*
     * If the next entry is going to be too big for the code size,
     * then increase it, if possible.
     */
   if ( free_ent > maxcode || clear_flg ) {

            if( clear_flg ) {
	    
                maxcode = MAXCODE (n_bits = g_init_bits);
                clear_flg = 0;
		
            } else {
	    
                n_bits++;
                if ( n_bits == maxbits )
                    maxcode = maxmaxcode;
                else
                    maxcode = MAXCODE(n_bits);
            }
        }
	
    if( code == EOFCode ) {
        /*
         * At EOF, write the rest of the buffer.
         */
        while( cur_bits > 0 ) {
    	        char_out( (unsigned int)(cur_accum & 0xff) );
	        cur_accum >>= 8;
	        cur_bits -= 8;
        }

	flush_char();
	
        fflush( g_outfile );

	if( ferror( g_outfile ) )
                writeerr();
    }
}

/*
 * Clear out the hash table
 */
static
cl_block ()             /* table clear for block compress */
{

        cl_hash ( (count_int) hsize );
        free_ent = ClearCode + 2;
        clear_flg = 1;

        output( (code_int)ClearCode );
}

static
cl_hash(hsize)          /* reset code table */
register count_int hsize;
{

        register count_int *htab_p = htab+hsize;

        register long i;
        register long m1 = -1;

        i = hsize - 16;
        do {                            /* might use Sys V memset(3) here */
                *(htab_p-16) = m1;
                *(htab_p-15) = m1;
                *(htab_p-14) = m1;
                *(htab_p-13) = m1;
                *(htab_p-12) = m1;
                *(htab_p-11) = m1;
                *(htab_p-10) = m1;
                *(htab_p-9) = m1;
                *(htab_p-8) = m1;
                *(htab_p-7) = m1;
                *(htab_p-6) = m1;
                *(htab_p-5) = m1;
                *(htab_p-4) = m1;
                *(htab_p-3) = m1;
                *(htab_p-2) = m1;
                *(htab_p-1) = m1;
                htab_p -= 16;
        } while ((i -= 16) >= 0);

	for ( i += 16; i > 0; i-- )
                *--htab_p = m1;
}

static
writeerr()
{
	printf( "error writing output file\n" );
	exit(1);
}

/******************************************************************************
 *
 * GIF Specific routines
 *
 ******************************************************************************/

/*
 * Number of characters so far in this 'packet'
 */
static int a_count;

/*
 * Set up the 'byte output' routine
 */
static
char_init()
{
	a_count = 0;
}

/*
 * Define the storage for the packet accumulator
 */
static char accum[ 256 ];

/*
 * Add a character to the end of the current packet, and if it is 254
 * characters, flush the packet to disk.
 */
static
char_out( c )
int c;
{
	accum[ a_count++ ] = c;
	if( a_count >= 254 ) 
		flush_char();
}

/*
 * Flush the packet to disk, and reset the accumulator
 */
static
flush_char()
{
	if( a_count > 0 ) {
		fputc( a_count, g_outfile );
		fwrite( accum, 1, a_count, g_outfile );
		a_count = 0;
	}
}	

/* The End */
@//E*O*F gifcompr.c//
chmod u=rw,g=r,o=r gifcompr.c
 
echo x - gifencod.c
sed 's/^@//' > "gifencod.c" <<'@//E*O*F gifencod.c//'

/*****************************************************************************
 *
 * GIFENCODE.C    - GIF Image compression interface
 *
 * GIFEncode( FName, GHeight, GWidth, GInterlace, Background, 
 *	      BitsPerPixel, Red, Green, Blue, GetPixel )
 *
 *****************************************************************************/
 
#include <stdio.h>

/*
 * Pointer to function returning an int
 */
typedef int (* ifunptr)();

#define TRUE 1
#define FALSE 0

static int Width, Height;
static int curx, cury;
static long CountDown;
static int Pass = 0;
static int Interlace;

/*
 * Bump the 'curx' and 'cury' to point to the next pixel
 */
static
BumpPixel()
{
	/*
	 * Bump the current X position
	 */
	curx++;

	/*
	 * If we are at the end of a scan line, set curx back to the beginning
	 * If we are interlaced, bump the cury to the appropriate spot,
	 * otherwise, just increment it.
	 */
	if( curx == Width ) {
		curx = 0;

	        if( !Interlace ) 
			cury++;
		else {
		     switch( Pass ) {
	     
	               case 0:
        	          cury += 8;
                	  if( cury >= Height ) {
		  		Pass++;
				cury = 4;
		  	  }
                          break;
		  
	               case 1:
        	          cury += 8;
                	  if( cury >= Height ) {
		  		Pass++;
				cury = 2;
		  	  }
			  break;
		  
	               case 2:
	                  cury += 4;
	                  if( cury >= Height ) {
	                     Pass++;
	                     cury = 1;
	                  }
	                  break;
			  
	               case 3:
	                  cury += 2;
	                  break;
			}
		}
	}
}

/*
 * Return the next pixel from the image
 */
GIFNextPixel( getpixel )
ifunptr getpixel;
{
	int r;

	if( CountDown == 0 )
		return EOF;

	CountDown--;

	r = ( * getpixel )( curx, cury );

	BumpPixel();

	return r;
}

/* public */

GIFEncode( FName, GWidth, GHeight, GInterlace, Background, 
	   BitsPerPixel, Red, Green, Blue, GetPixel )
	 
char *FName;
int GWidth, GHeight;
int GInterlace;
int Background;
int BitsPerPixel;
int Red[], Green[], Blue[];
ifunptr GetPixel;

{
	FILE *fp;
	int B;
	int RWidth, RHeight;
	int LeftOfs, TopOfs;
	int Resolution;
	int ColorMapSize;
	int InitCodeSize;
	int i;

	Interlace = GInterlace;
	
	ColorMapSize = 1 << BitsPerPixel;
	
	RWidth = Width = GWidth;
	RHeight = Height = GHeight;
	LeftOfs = TopOfs = 0;
	
	Resolution = BitsPerPixel;

	/*
	 * Calculate number of bits we are expecting
	 */
	CountDown = (long)Width * (long)Height;

	/*
	 * Indicate which pass we are on (if interlace)
	 */
	Pass = 0;

	/*
	 * The initial code size
	 */
	if( BitsPerPixel <= 1 )
		InitCodeSize = 2;
	else
		InitCodeSize = BitsPerPixel;

	/*
	 * Set up the current x and y position
	 */
	curx = cury = 0;

	/*
	 * Open the GIF file for binary write
	 */
	fp = fopen( FName, "wb" );

	if( fp == (FILE *)0 ) {
		printf( "error: could not open output file\n" );
		exit(1);
	}

	/*
	 * Write the Magic header
	 */
	fwrite( "GIF87a", 1, 6, fp );

	/*
	 * Write out the screen width and height
	 */
	Putword( RWidth, fp );
	Putword( RHeight, fp );

	/*
	 * Indicate that there is a global colour map
	 */
	B = 0x80;	/* Yes, there is a color map */

	/*
	 * OR in the resolution
	 */
	B |= (Resolution - 1) << 5;

	/*
	 * OR in the Bits per Pixel
	 */
	B |= (BitsPerPixel - 1);

	/*
	 * Write it out
	 */
	fputc( B, fp );

	/*
	 * Write out the Background colour
	 */
	fputc( Background, fp );

	/*
	 * Byte of 0's (future expansion)
	 */
	fputc( 0, fp );

	/*
	 * Write out the Global Colour Map
	 */
     	for( i=0; i<ColorMapSize; i++ ) {
		fputc( Red[i], fp );
		fputc( Green[i], fp );
		fputc( Blue[i], fp );
	}

	/*
	 * Write an Image separator
	 */
	fputc( ',', fp );

	/*
	 * Write the Image header
	 */

	Putword( LeftOfs, fp );
	Putword( TopOfs, fp );
	Putword( Width, fp );
	Putword( Height, fp );

	/*
	 * Write out whether or not the image is interlaced
	 */
	if( Interlace )
		fputc( 0x40, fp );
	else
		fputc( 0x00, fp );

	/*
	 * Write out the initial code size
	 */
	fputc( InitCodeSize, fp );

	/*
	 * Go and actually compress the data
	 */
	compress( InitCodeSize+1, fp, GetPixel );

	/*
	 * Write out a Zero-length packet (to end the series)
	 */
	fputc( 0, fp );

	/*
	 * Write the GIF file terminator
	 */
	fputc( ';', fp );

	/*
	 * And close the file
	 */
	fclose( fp );
	
}

/*
 * Write out a word to the GIF file
 */
static
Putword( w, fp )
int w;
FILE *fp;
{
	fputc( w & 0xff, fp );
	fputc( (w / 256) & 0xff, fp );
}

@//E*O*F gifencod.c//
chmod u=rw,g=r,o=r gifencod.c
 
exit 0