Category : C Source Code
Archive   : ENCODER.ZIP
Filename : GIFCOMPR.C

/***************************************************************************
*
* GIFENCOD.C - GIF Image compression routines
*
* Lempel-Ziv compression based on 'compress'. GIF modifications by
* David Rowley ([email protected])
*
***************************************************************************/

/*
* 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
#include
#include

#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<
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 */