gd_gif_out.c

PHP v6.0 For Linux 运行环境：Win9X/ WinME/ WinNT/ Win2K/ WinXP

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

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

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

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

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

/***************************************************************************
 *
 *  GIFCOMPR.C       - GIF Image compression routines
 *
 *  Lempel-Ziv compression based on 'compress'.  GIF modifications by
 *  David Rowley ([e-mail])
 *
 ***************************************************************************/

/*
 * General DEFINEs
 */

#define GIFBITS    12

#ifdef NO_UCHAR
 typedef char   char_type;
#else /*NO_UCHAR*/
 typedef        unsigned char   char_type;
#endif /*NO_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 <ctype.h>

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

#ifdef COMPATIBLE               /* But wrong! */
# define MAXCODE(n_bits)        ((code_int) 1 << (n_bits) - 1)
#else /*COMPATIBLE*/
# define MAXCODE(n_bits)        (((code_int) 1 << (n_bits)) - 1)
#endif /*COMPATIBLE*/

#define HashTabOf(i)       ctx->htab[i]
#define CodeTabOf(i)    ctx->codetab[i]


/*
 * 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**GIFBITS 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<<GIFBITS))

/*
 * 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 void
output(code_int code, GifCtx *ctx);

static void
compress(int init_bits, gdIOCtxPtr outfile, gdImagePtr im, GifCtx *ctx)
{
    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
     */
    ctx->g_init_bits = init_bits;
    ctx->g_outfile = outfile;

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

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

    char_init(ctx);

    ent = GIFNextPixel( im, ctx );

    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, ctx );            /* clear hash table */

    output( (code_int)ctx->ClearCode, ctx );

#ifdef SIGNED_COMPARE_SLOW
    while ( (c = GIFNextPixel( im )) != (unsigned) EOF ) {
#else /*SIGNED_COMPARE_SLOW*/
    while ( (c = GIFNextPixel( im, ctx )) != EOF ) {  /* } */
#endif /*SIGNED_COMPARE_SLOW*/

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

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

static void
output(code_int code, GifCtx *ctx)
{
    ctx->cur_accum &= masks[ ctx->cur_bits ];

    if( ctx->cur_bits > 0 )
        ctx->cur_accum |= ((long)code << ctx->cur_bits);
    else
        ctx->cur_accum = code;

    ctx->cur_bits += ctx->n_bits;

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

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

            if( ctx->clear_flg ) {

                ctx->maxcode = MAXCODE (ctx->n_bits = ctx->g_init_bits);
                ctx->clear_flg = 0;

            } else {

                ++(ctx->n_bits);
                if ( ctx->n_bits == maxbits )
                    ctx->maxcode = maxmaxcode;
                else
                    ctx->maxcode = MAXCODE(ctx->n_bits);
            }
        }

    if( code == ctx->EOFCode ) {
        /*
         * At EOF, write the rest of the buffer.
         */
        while( ctx->cur_bits > 0 ) {
                char_out( (unsigned int)(ctx->cur_accum & 0xff), ctx);
                ctx->cur_accum >>= 8;
                ctx->cur_bits -= 8;
        }

        flush_char(ctx);

    }
}

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

        cl_hash ( (count_int) hsize, ctx );
        ctx->free_ent = ctx->ClearCode + 2;
        ctx->clear_flg = 1;

        output( (code_int)ctx->ClearCode, ctx);
}

static void
cl_hash(register count_int chsize, GifCtx *ctx)          /* reset code table */
                         
{

        register count_int *htab_p = ctx->htab+chsize;

        register long i;
        register long m1 = -1;

        i = chsize - 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;
}

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

/*
 * Set up the 'byte output' routine
 */
static void
char_init(GifCtx *ctx)
{
        ctx->a_count = 0;
}

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

/*
 * Flush the packet to disk, and reset the accumulator
 */
static void
flush_char(GifCtx *ctx)
{
        if( ctx->a_count > 0 ) {
                gdPutC( ctx->a_count, ctx->g_outfile );
                gdPutBuf( ctx->accum, ctx->a_count, ctx->g_outfile );
                ctx->a_count = 0;
        }
}

static int gifPutWord(int w, gdIOCtx *out)
{
	/* Byte order is little-endian */
	gdPutC(w & 0xFF, out);
	gdPutC((w >> 8) & 0xFF, out);
	return 0;
}