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#include "ImageIO.h"
#include "gif.h"
#ifdef WIN32
#include <io.h>
#define _CRT_SECURE_NO_WARNINGS
#endif

typedef int boolean;
typedef unsigned char byte;
#define TRUE 1
#define FALSE 0

#define EXTENSION     0x21
#define IMAGESEP      0x2c
#define TRAILER       0x3b
#define INTERLACEMASK 0x40
#define COLORMAPMASK  0x80


#define DEBUG 0

FILE *fp;
int   gif89 = 0;
char *id87 = "GIF87a";
char *id89 = "GIF89a";

static int EGApalette[16][3] = {
  {0,0,0},       {0,0,128},     {0,128,0},     {0,128,128}, 
  {128,0,0},     {128,0,128},   {128,128,0},   {200,200,200},
  {100,100,100}, {100,100,255}, {100,255,100}, {100,255,255},
  {255,100,100}, {255,100,255}, {255,255,100}, {255,255,255} };
  

static int  ReadCode();
static void DoInterlace(byte);
static int GifError(char *);


byte *Raster;			/* The raster data stream, unblocked */
byte *RawGIF;
byte *r,*g,*b;                  /* The colormap */
int BitOffset = 0,		/* Bit Offset of next code */
  XC = 0, YC = 0,		/* Output X and Y coords of current pixel */
  CodeSize,			/* Code size, read from GIF header */
  ReadMask,			/* Code AND mask for current code size */
  Pass = 0,			/* Used by output routine if interlaced pic */
  Width, Height;		/* image dimensions */

unsigned char *org, *buf;


/*****************************/
int readGifImage(_image *im,const char *name) {
  register byte ch, ch1;
  register byte *ptr, *ptr1;
  register int i, block;
  int npixels, maxpixels, aspect, filesize;
  float normaspect;
  int OutCount = 0,		/* Decompressor output 'stack count' */
    RWidth, RHeight,		/* screen dimensions */
    /*LeftOfs, TopOfs,		 image offset */
    BitsPerPixel,		/* Bits per pixel, read from GIF header */
    ColorMapSize,		/* number of colors */
    Background,		         /* background color */
    InitCodeSize,		/* Starting code size, used during Clear */
    Code,			/* Value returned by ReadCode */
    MaxCode,			/* limiting value for current code size */
    ClearCode,			/* GIF clear code */
    EOFCode,			/* GIF end-of-information code */
    CurCode, OldCode, InCode,	/* Decompressor variables */
    FirstFree,			/* First free code, generated per GIF spec */
    FreeCode,			/* Decompressor,next free slot in hash table */
    FinChar,			/* Decompressor variable */
    BitMask,			/* AND mask for data size */
    Misc;                       /* miscellaneous bits (interlace, local cmap)*/
  boolean Interlace, HasColormap;
//  char header[10];

  /* The hash table used by the decompressor */
  int Prefix[4096];
  int Suffix[4096];
  /* An output array used by the decompressor */
  int OutCode[4097];

  /* initialize variables */
  BitOffset = XC = YC = Pass = OutCount = npixels = maxpixels = 0;
  FinChar = OldCode = 0;
  RawGIF = Raster = NULL;
  gif89 = 0;

#ifdef WIN32
 fp = fopen(name,"rb");
#else
  fp = fopen(name,"r");
#endif
//  fp = fopen(name,"rb");
  if (!fp) {
    return(GifError("could not open a GIF file"));
  }
  /* find the size of the file */
  fseek(fp, 0L, 2);
  filesize = ftell(fp);
  fseek(fp, 0L, 0);

 /* the +256's are so we can read truncated GIF files without fear of segmentation violation */
  if (!(ptr = RawGIF = (byte *) ImageIO_alloc(filesize+256)))
    return( GifError("not enough memory to read gif file") );
  
  if (!(Raster = (byte *) ImageIO_alloc(filesize+256)))    
    return( GifError("not enough memory to read gif file") );
  
  if (fread(ptr, filesize, 1, fp) != 1)
    return( GifError("GIF data read failed") );
   if      (strncmp((char *) ptr, id87, 6)==0) gif89 = 0;
  else if (strncmp((char *) ptr, id89, 6)==0) gif89 = 1;
  else    return( GifError("not a GIF file"));
  
  ptr += 6;
 /* Get variables from the GIF screen descriptor */
  
  ch = (*ptr++);
  RWidth = ch + 0x100 * (*ptr++);	/* screen dimensions... not used. */
  ch = (*ptr++);
  RHeight = ch + 0x100 * (*ptr++);
  
  ch = (*ptr++);
  HasColormap = ((ch & COLORMAPMASK) ? TRUE : FALSE);
  
  BitsPerPixel = (ch & 7) + 1;
  ColorMapSize = 1 << BitsPerPixel;
  BitMask = ColorMapSize - 1;
  
  Background = (*ptr++);		/* background color... not used. */


  aspect = (*ptr++);
  if (aspect) {
    if (!gif89) return(GifError("corrupt GIF file (screen descriptor)"));
    else normaspect = (float) ((aspect + 15) / 64.0);   /* gif89 aspect ratio */
    if (DEBUG) fprintf(stderr,"GIF89 aspect = %f\n", normaspect);
  }


  /* Read in global colormap. */
  if (HasColormap)
    {
      r = (byte *) ImageIO_alloc(ColorMapSize * sizeof(byte));
      g = (byte *) ImageIO_alloc(ColorMapSize * sizeof(byte));
      b = (byte *) ImageIO_alloc(ColorMapSize * sizeof(byte));

      for (i = 0; i < ColorMapSize; i++) {
	r[i] = (*ptr++);
	g[i] = (*ptr++);
	b[i] = (*ptr++);
      }
    }
  else {
    /* no colormap in GIF file */
    /* put std EGA palette (repeated 16 times) into colormap, for lack of
       anything better to do */
    ColorMapSize = 256;
    r = (byte *) ImageIO_alloc(256 * sizeof(byte));
    g = (byte *) ImageIO_alloc(256 * sizeof(byte));
    b = (byte *) ImageIO_alloc(256 * sizeof(byte));
   
    for (i = 0; i < 256; i++) {
      r[i] = EGApalette[i&15][0];
      g[i] = EGApalette[i&15][1];
      b[i] = EGApalette[i&15][2];
    }
  }

  /* possible things at this point are:
   *   an application extension block
   *   a comment extension block
   *   an (optional) graphic control extension block
   *       followed by either an image
   *	   or a plaintext extension
   */
  while (1) {
    block = (*ptr++);
   
    if (block == EXTENSION) {  /* parse extension blocks */
      int i, fn, blocksize, aspnum, aspden;
	  
      /* read extension block */
      fn = (*ptr++);
	  
      if (DEBUG) fprintf(stderr,"GIF extension type 0x%02x\n", fn);
	  
      if (fn == 'R') {                  /* GIF87 aspect extension */
	blocksize = (*ptr++);
	if (blocksize == 2) {
	  aspnum = (*ptr++);
	  aspden = (*ptr++);
	  if (aspden>0 && aspnum>0) 
	    normaspect = (float) aspnum / (float) aspden;
	  else { normaspect = 1.0;  aspnum = aspden = 1; }
			
	  if (DEBUG) fprintf(stderr,"GIF87 aspect extension: %d:%d = %f\n\n", 
			     aspnum, aspden,normaspect);
	}
	else {
	  for (i=0; i<blocksize; i++) ptr++;
	}
      }
	  
      else if (fn == 0xFE) {  /* Comment Extension.  just eat it */
	int ch, j, sbsize;
		 
	if (DEBUG) fprintf(stderr,"Comment extension:  ");
	/* read (and ignore) data sub-blocks */
	do {
	  j = 0;  sbsize = (*ptr++);
	  while (j<sbsize) {
	    ch = (*ptr++);  j++;
	    if (DEBUG) fprintf(stderr,"%c", ch);
	  }
	} while (sbsize);
	if (DEBUG) fprintf(stderr,"\n\n");
      }
	  
      else if (fn == 0x01) {  /* PlainText Extension */
	int j,sbsize,ch;
	int tgLeft, tgTop, tgWidth, tgHeight, cWidth, cHeight, fg, bg;
		 
	/*	SetISTR(ISTR_WARNING, 
		"PlainText extension found in GIF file.  Ignored.");*/
		 
	sbsize   = (*ptr++);
	tgLeft   = (*ptr++);  tgLeft   += ((*ptr++))<<8;
	tgTop    = (*ptr++);  tgTop    += ((*ptr++))<<8;
	tgWidth  = (*ptr++);  tgWidth  += ((*ptr++))<<8;
	tgHeight = (*ptr++);  tgHeight += ((*ptr++))<<8;
	cWidth   = (*ptr++);
	cHeight  = (*ptr++);
	fg       = (*ptr++);
	bg       = (*ptr++);
	i=12;
	for ( ; i<sbsize; i++) ptr++;   /* read rest of first subblock */
		 
	if (DEBUG) fprintf(stderr,
			   "PlainText: tgrid=%d,%d %dx%d  cell=%dx%d  col=%d,%d\n",
			   tgLeft, tgTop, tgWidth, tgHeight, cWidth, cHeight,
			   fg, bg);
		 
	/* read (and ignore) data sub-blocks */
	do {
	  j = 0;
	  sbsize = (*ptr++);
	  while (j<sbsize) {
	    ch = (*ptr++);  j++;
	    if (DEBUG) fprintf(stderr,"%c", ch);
	  }
	} while (sbsize);
	if (DEBUG) fprintf(stderr,"\n\n");
      }
	  
	  
      else if (fn == 0xF9) {  /* Graphic Control Extension */
	int j, sbsize;
		 
	if (DEBUG) fprintf(stderr,"Graphic Control extension\n\n");
		 
	/*	SetISTR(ISTR_WARNING, 
		"Graphic Control Extension in GIF file.  Ignored.");*/
		 
	/* read (and ignore) data sub-blocks */
	do {
	  j = 0; sbsize = (*ptr++);
	  while (j<sbsize) { ptr++;  j++; }
	} while (sbsize);
      }
      
	  
      else { /* unknown extension */
	int j, sbsize;
		 
	if (DEBUG) fprintf(stderr,"unknown GIF extension 0x%02x\n\n", fn);
		 
	/*	SetISTR(ISTR_WARNING, 
		"Unknown extension 0x%02x in GIF file.  Ignored.",fn);*/
		 
	/* read (and ignore) data sub-blocks */
	do {
	  j = 0; sbsize = (*ptr++);
	  while (j<sbsize) { ptr++;  j++; }
	} while (sbsize);
      }
    }
   
    else if (block == IMAGESEP) break;   /* read an image */

    else if (block == TRAILER) {
      return( GifError("no image data found in GIF file") );
    }
   
    else return (GifError("Unknown block type found in file."));
  }


  /* read in values from the image descriptor */
  ch = (*ptr++);
  /* LeftOfs = ch + 0x100 * (*ptr++);*/
  ch = (*ptr++);
  /* TopOfs = ch + 0x100 * (*ptr++); */
  ch = (*ptr++);
  ch = (*ptr++);
  ch = (*ptr++);
  Width = ch + 0x100 * (*ptr++);
  ch = (*ptr++);
  Height = ch + 0x100 * (*ptr++);

  Misc = (*ptr++);
  Interlace = ((Misc & INTERLACEMASK) ? TRUE : FALSE);

  if (Misc & 0x80) {
    for (i=0; i< 1 << ((Misc&7)+1); i++) {
      r[i] = (*ptr++);
      g[i] = (*ptr++);
      b[i] = (*ptr++);
    }
  }


  if (!HasColormap && !(Misc&0x80)) {
    /* no global or local colormap */
    /*    SetISTR(ISTR_WARNING,
	  "No colormap in this GIF file.  Assuming EGA colors.");*/
  }



  /* Start reading the raster data. First we get the intial code size
   * and compute decompressor constant values, based on this code size.
   */
  
  /*  SetISTR(ISTR_FORMAT, "GIF%s, %d bits per pixel, %sinterlaced.  (%d bytes)",
      (gif89) ? "89" : "87", BitsPerPixel, 
      Interlace ? "" : "non-", filesize);*/

  CodeSize = (*ptr++);

  ClearCode = (1 << CodeSize);
  EOFCode = ClearCode + 1;
  FreeCode = FirstFree = ClearCode + 2;

  /* The GIF spec has it that the code size is the code size used to
   * compute the above values is the code size given in the file, but the
   * code size used in compression/decompression is the code size given in
   * the file plus one. (thus the ++).
   */
  CodeSize++;
  InitCodeSize = CodeSize;
  MaxCode = (1 << CodeSize);
  ReadMask = MaxCode - 1;

  /* UNBLOCK:
   * Read the raster data.  Here we just transpose it from the GIF array
   * to the Raster array, turning it from a series of blocks into one long
   * data stream, which makes life much easier for ReadCode().
   */
  
  ptr1 = Raster;
  do {
    ch = ch1 = (*ptr++);
    while (ch--) { 
		*ptr1 = (*ptr++); 
		ptr1++; }
    if ((ptr - RawGIF) > filesize) {
      /*      SetISTR(ISTR_WARNING,
	      "This GIF file seems to be truncated.  Winging it.");*/
      break;
    }
  } while(ch1);
  ImageIO_free(RawGIF);  RawGIF = NULL;


  if (DEBUG) {
    fprintf(stderr,"xv: LoadGIF() - picture is %dx%d, %d bits, %sinterlaced\n",
	    Width, Height, BitsPerPixel, Interlace ? "" : "non-");
  }
  

  /* Allocate the 'pic' */
  maxpixels = Width*Height;
  im->xdim = Width;
  im->ydim = Height;
  im->zdim = 1;
  im->vdim = 3;
  im->wdim = 1;
  im->wordKind = WK_FIXED;
  im->sign = SGN_UNSIGNED;
  im->data = ImageIO_alloc(Width * Height * 3);
  org = buf = (unsigned char *) im->data;

  if (!org)
    return( GifError("not enough memory for image buffer") );


  /* Decompress the file, continuing until you see the GIF EOF code.
   * One obvious enhancement is to add checking for corrupt files here.
   */
  Code = ReadCode();
  while (Code != EOFCode) {
   /* Clear code sets everything back to its initial value, then reads the
     * immediately subsequent code as uncompressed data.
     */
   
	  if (Code == ClearCode) { 
      CodeSize = InitCodeSize;
      MaxCode = (1 << CodeSize);
      ReadMask = MaxCode - 1;
      FreeCode = FirstFree;
      Code = ReadCode();
      CurCode = OldCode = Code;
      FinChar = CurCode & BitMask;
      if (!Interlace) {
	*buf++ = r[FinChar];
	*buf++ = g[FinChar];
	*buf++ = b[FinChar];
      }
      else DoInterlace(FinChar);
      npixels++;
    }

    else {
      /* If not a clear code, must be data: save same as CurCode and InCode */
	   
      /* if we're at maxcode and didn't get a clear, stop loading */
      if (FreeCode>=4096) { 
		  printf("freecode blew up\n"); 
	      break;
	  }
	   
      CurCode = InCode = Code;
	   
      /* If greater or equal to FreeCode, not in the hash table yet;
       * repeat the last character decoded
       */
	   
      if (CurCode >= FreeCode) {
	CurCode = OldCode;
	if (OutCount > 4096) {   
		printf("outcount1 blew up\n");  break; }
	OutCode[OutCount++] = FinChar;
      }
	   
      /* Unless this code is raw data, pursue the chain pointed to by CurCode
       * through the hash table to its end; each code in the chain puts its
       * associated output code on the output queue.
       */
	   
      while (CurCode > BitMask) {
		  if (OutCount > 4096) {
			  fprintf(stderr,"outcount2 blew up\n"); break;}   /* corrupt file */
	OutCode[OutCount++] = Suffix[CurCode];
	CurCode = Prefix[CurCode];
      }
	   
      if (OutCount > 4096) {  
		  printf("outcount blew up\n");  break; }
	   
      /* The last code in the chain is treated as raw data. */
	   
      FinChar = CurCode & BitMask;
      OutCode[OutCount++] = FinChar;
	   
      /* Now we put the data out to the Output routine.
       * It's been stacked LIFO, so deal with it that way...
       */

      /* safety thing:  prevent exceeding range of 'pic' */
      if (npixels + OutCount > maxpixels) OutCount = maxpixels-npixels;
	   
      npixels += OutCount;
      if (!Interlace) for (i=OutCount-1; i>=0; i--) {
	*buf++ = r[OutCode[i]];
	*buf++ = g[OutCode[i]];
	*buf++ = b[OutCode[i]];
      }
      else  for (i=OutCount-1; i>=0; i--) DoInterlace(OutCode[i]);
      OutCount = 0;
	   
      /* Build the hash table on-the-fly. No table is stored in the file. */
      
      Prefix[FreeCode] = OldCode;
      Suffix[FreeCode] = FinChar;
      OldCode = InCode;
	   
      /* Point to the next slot in the table.  If we exceed the current
       * MaxCode value, increment the code size unless it's already 12.  If it
       * is, do nothing: the next code decompressed better be CLEAR
       */
	   
      FreeCode++;
      if (FreeCode >= MaxCode) {
	if (CodeSize < 12) {
	  CodeSize++;
	  MaxCode *= 2;
	  ReadMask = (1 << CodeSize) - 1;
	}
      }
    }
    Code = ReadCode();
    if (npixels >= maxpixels) break;
  }
  ImageIO_free(Raster);  Raster = NULL;

  if (npixels != maxpixels) {
    /*    SetISTR(ISTR_WARNING,"This GIF file seems to be truncated.  Winging it.");*/
    if (!Interlace)
      memset(buf, 0, 3*(maxpixels-npixels)); /* clear to EOBuffer */
  }
  /*  SetDirRButt(F_FORMAT, F_GIF);
      SetDirRButt(F_COLORS, F_FULLCOLOR);*/
  return 1;
}


/* Fetch the next code from the raster data stream.  The codes can be
 * any length from 3 to 12 bits, packed into 8-bit bytes, so we have to
 * maintain our location in the Raster array as a BIT Offset.  We compute
 * the byte Offset into the raster array by dividing this by 8, pick up
 * three bytes, compute the bit Offset into our 24-bit chunk, shift to
 * bring the desired code to the bottom, then mask it off and return it. 
 */

static int ReadCode()
{
  int RawCode, ByteOffset;
  
  ByteOffset = BitOffset / 8;
  RawCode = Raster[ByteOffset] + (Raster[ByteOffset + 1] << 8);
  if (CodeSize >= 8)
    RawCode += ( ((int) Raster[ByteOffset + 2]) << 16);
  RawCode >>= (BitOffset % 8);
  BitOffset += CodeSize;

  return(RawCode & ReadMask);
}


/***************************/
static void DoInterlace(byte Index) {
  static byte *ptr = NULL;
  static int   oldYC = -1;
  
  if (oldYC != YC) {
    ptr = org + 3 * YC * Width;
    oldYC = YC;
  }
  
  if (YC < Height) {
    *ptr++ = r[Index];
    *ptr++ = g[Index];
    *ptr++ = b[Index];
  }
  
  /* Update the X-coordinate, and if it overflows, update the Y-coordinate */
  if (++XC == Width) {
    
    /* deal with the interlace as described in the GIF
     * spec.  Put the decoded scan line out to the screen if we haven't gone
     * past the bottom of it
     */
    
    XC = 0;
    
    switch (Pass) {
    case 0:
      YC += 8;
      if (YC >= Height) { Pass++; YC = 4; }
      break;
      
    case 1:
      YC += 8;
      if (YC >= Height) { Pass++; YC = 2; }
      break;
      
    case 2:
      YC += 4;
      if (YC >= Height) { Pass++; YC = 1; }
      break;
      
    case 3:
      YC += 2;  break;
      
    default:
      break;
    }
  }
}


      
/*****************************/
static int GifError(char *st) {
  fprintf(stderr,"readGifImage: error: %s\n",st);

  if (RawGIF != NULL) ImageIO_free(RawGIF);
  if (Raster != NULL) ImageIO_free(Raster);
  
  return -1;
}