/*****************************************************************
 * Portions of this code Copyright (C) 1989 by Michael Mauldin.
 * Permission is granted to use this file in whole or in
 * part for any purpose, educational, recreational or commercial,
 * provided that this copyright notice is retained unchanged.
 * This software is available to all free of charge by anonymous
 * FTP and in the UUNET archives.
 *
 *
 * Authors:  Michael Mauldin (mlm@cs.cmu.edu)
 *           David Rowley (mgardi@watdcsu.waterloo.edu)
 *
 * Based on: compress.c - File compression ala IEEE Computer, June 1984.
 *
 * 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 <string.h>

static int Width, Height;
static int curx, cury;
static long CountDown;

static void putword (int, FILE *);
static void compress (int, FILE *, unsigned char *, int);
static void output (int);
static void cl_block (void);
static void cl_hash (long);
static void char_init (void);
static void char_out (int);
static void flush_char (void);

static unsigned char pc2nc[256], r1[256], g1[256], b1[256];

/*************************************************************/
void
WriteGIF (
           FILE * fp,
           unsigned char *pic,
           int w,
           int h,
           unsigned char *rmap,
           unsigned char *gmap,
           unsigned char *bmap,
           int numcols)
{
  int RWidth, RHeight;
  int LeftOfs, TopOfs;
  int ColorMapSize, InitCodeSize, BitsPerPixel;
  int i, j, nc;

  for (i = 0; i < 256; i++)
  {
    pc2nc[i] = r1[i] = g1[i] = b1[i] = 0;
  }

  /* compute number of unique colors */
  nc = 0;

  for (i = 0; i < numcols; i++)
  {
    /* see if color #i is already used */
    for (j = 0; j < i; j++)
    {
      if (rmap[i] == rmap[j] &&
          gmap[i] == gmap[j] &&
          bmap[i] == bmap[j])
      {
        break;
      }
    }

    if (j == i)
    {                           /* wasn't found */
      pc2nc[i] = nc;
      r1[nc] = rmap[i];
      g1[nc] = gmap[i];
      b1[nc] = bmap[i];
      nc++;
    }
    else
    {
      pc2nc[i] = pc2nc[j];
    }
  }

  /* figure out 'BitsPerPixel' */
  for (i = 1; i < 8; i++)
  {
    if ((1 << i) >= nc)
    {
      break;
    }
  }

  BitsPerPixel = i;

  ColorMapSize = 1 << BitsPerPixel;

  RWidth = Width = w;
  RHeight = Height = h;
  LeftOfs = TopOfs = 0;

  CountDown = w * h;            /* # of pixels we'll be doing */

  if (BitsPerPixel <= 1)
    InitCodeSize = 2;
  else
    InitCodeSize = BitsPerPixel;

  curx = cury = 0;

  fwrite ("GIF87a", 1, 6, fp);  /* the GIF magic number */

  putword (RWidth, fp);         /* screen descriptor */
  putword (RHeight, fp);

  i = 0x80;                     /* Yes, there is a color map */
  i |= (8 - 1) << 4;            /* OR in the color resolution (hardwired 8) */
  i |= (BitsPerPixel - 1);      /* OR in the # of bits per pixel */
  fputc (i, fp);

  fputc (0, fp);                /* background color */
  fputc (0, fp);                /* future expansion byte */

  for (i = 0; i < ColorMapSize; i++)
  {                             /* write out Global colormap */
    fputc (r1[i], fp);
    fputc (g1[i], fp);
    fputc (b1[i], fp);
  }

  fputc (',', fp);              /* image separator */

  /* Write the Image header */
  putword (LeftOfs, fp);
  putword (TopOfs, fp);
  putword (Width, fp);
  putword (Height, fp);
  fputc (0x00, fp);             /* Use Global Colormap */

  fputc (InitCodeSize, fp);
  compress (InitCodeSize + 1, fp, pic, w * h);

  fputc (0, fp);                /* Write out a Zero-length packet (EOF) */
  fputc (';', fp);              /* Write GIF file terminator */
}

/******************************/
static void
putword (int w, FILE * fp)
{
  /* writes a 16-bit integer in GIF order (LSB first) */
  fputc (w & 0xff, fp);
  fputc ((w >> 8) & 0xff, fp);
}

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

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

#define min(a,b) ((a>b) ? b : a)

#define BITS 12

#define HSIZE 5003             /* 80% occupancy */

typedef unsigned char char_type;


static int n_bits;              /* number of bits/code */
static int maxbits = BITS;      /* user settable max # bits/code */
static int maxcode;             /* maximum code, given n_bits */
static int maxmaxcode = 1 << BITS;  /* NEVER generate this */

#define MAXCODE(n_bits) ( (1 << (n_bits)) - 1)

static long htab[HSIZE];
static unsigned short codetab[HSIZE];

#define HashTabOf(i) htab[i]
#define CodeTabOf(i) codetab[i]

static int hsize = HSIZE;       /* for dynamic table sizing */

/*
 * 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(1<<BITS))

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

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

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;

/********************************************************/
static void
compress (int init_bits, FILE * outfile, unsigned char *data, int len)
{
  register long fcode;
  register int i = 0;
  register int c;
  register int ent;
  register int disp;
  register 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;

  /* initialize 'compress' globals */
  maxbits = BITS;
  maxmaxcode = 1 << BITS;
  memset ((char *) htab, 0, sizeof (htab));
  memset ((char *) codetab, 0, sizeof (codetab));
  hsize = HSIZE;
  free_ent = 0;
  clear_flg = 0;
  in_count = 1;
  out_count = 0;
  cur_accum = 0;
  cur_bits = 0;


  /*
   * Set up the necessary values
   */
  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 = pc2nc[*data++];
  len--;

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

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

  output (ClearCode);

  while (len)
  {
    c = pc2nc[*data++];
    len--;
    in_count++;

    fcode = (long) (((long) c << maxbits) + ent);
    i = (((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 (ent);
    out_count++;
    ent = c;

    if (free_ent < maxmaxcode)
    {
      CodeTabOf (i) = free_ent++;  /* code -> hashtable */
      HashTabOf (i) = fcode;
    }
    else
    {
      cl_block ();
    }
  }

  /* Put out the final code */
  output (ent);
  out_count++;
  output (EOFCode);
}


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

static void
output (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);
  }
}

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

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

  output (ClearCode);
}

/********************************/
static void
cl_hash (long hsize)            /* reset code table */
{
  register long *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;
}

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

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

/*
 * Set up the 'byte output' routine
 */
static void
char_init (void)
{
  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 void
char_out (int c)
{
  accum[a_count++] = c;
  if (a_count >= 254)
    flush_char ();
}

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