/***************************************************************************

 *

 *  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 */