#include <stdio.h>                
#include <stdlib.h>               
#include "gif.h"                  

int EndianOrder;
int i;


WORD 
GetWord (MemGif)
BYTE *MemGif;
{
	register WORD w;
	if (EndianOrder == 1) /* LittleEndian */
	{
		w  = (WORD) (*MemGif++ & 0xFF);
		w |= (WORD) ((*MemGif++ & 0xFF) << 0x08);
	}
	else
	{
		w = (WORD) (*MemGif++ & 0xFF);
		w = ((WORD) (*MemGif++ & 0xFF)) | (w << 0x08);
	}
	return w;
}

BYTE
GetByte (MemGif)
BYTE *MemGif;
{	
	return *MemGif;
}

/*
**  Read a GIF image BYTE Header.
**
**  This function reads the Header, Logical Screen Descriptor, and
**  Global Color Table (if any) from a GIF image file.  The information
**  is stored in a GIFHEAD structure.
**
**  Returns: -1 if a FILE stream error occured during the read,
**           otherwise 0 if no error occured.
*/
int
ReadGifHeader(GifHead, MemGif2)
GIFHEAD *GifHead;       /* Pointer to GIF header structure  */
BYTE    **MemGif2;       /* GIF image file input FILE stream */
{
    register WORD i;    /* Loop counter                                */
    WORD tableSize;     /* Number of entires in the Global Color Table */
	
	GifHead->TableSize = 0;
	for (i = 0 ; i < 6 ; i++) {
		GifHead->HeaderDump[i] = *(*MemGif2)++;
	}
	if (strncmp(GifHead->HeaderDump , "GIF" , 3)) {
		printf("The file does not appear to be a valid GIF file.\n");
		exit(-1);
	}
	
	for (i = 0 ; i < 7 ; i++) {
		GifHead->LSDDump[i] = *(*MemGif2)++;
	}

	GifHead->PackedField = GifHead->LSDDump[4];
	/* Check if a Global Color Table is present */
    if (GifHead->PackedField & 0x80)
    {
        /* Read number of color table entries */
        tableSize = (WORD) (1L << ((GifHead->PackedField & 0x07) + 1));
		GifHead->TableSize = tableSize;
        /* Read the Global Color Table */
		/* 
		** There are some changes made here apart from just
		** reading in the global color table as would
		** seem intuitively obvious.
		** The colors are stored in the bottom part of the 
		** palette as opposed to the top
		*/

        for (i = 0; i < tableSize; i++)
        {
            GifHead->HDFPalette[i][0] = *(*MemGif2)++;
            GifHead->HDFPalette[i][1] = *(*MemGif2)++;
            GifHead->HDFPalette[i][2] = *(*MemGif2)++;
        }
    }

    /* Check for a FILE stream error */
	/*
    if (ferror(FpGif))
        return(-1); 
	*/

    return(0);          /* No FILE stream error occured */
}


/*
**  Read a GIF Local Image Descriptor.
**
**  This function reads the Local Image Descriptor, and Local Color
**  Table (if any) from a GIF image file.  The information is stored
**  in a GIFIMAGEDESC structure.
**
**  Note that the ImageSeparator field value in the GIFIMAGEDESC
**  structure is assigned by the function calling ReadGifImageDesc().
**
**  Returns: -1 if a FILE stream error occured during the read,
**           otherwise 0 if no error occured.
*/
int
ReadGifImageDesc(GifImageDesc, MemGif2)
GIFIMAGEDESC *GifImageDesc; /* Pointer to GIF image descriptor structure  */
BYTE         **MemGif2;     /* GIF image file input FILE stream           */
{
    register WORD i;        /* Loop counter                               */
    WORD tableSize;         /* Number of entries in the Local Color Table */
	BYTE Interlace;         /* PackedField & 0x20 gives information on interlacing */
	BYTE *TempPtr;
	int	 ch , ch1;

	GifImageDesc->TableSize = 0;
	for (i = 0 ; i < 9 ; i++) {
		GifImageDesc->GIDDump[i] = *(*MemGif2)++;
	}
	
	/*
	** Get the relevant fields. I need ImageWidth and Height actively hence I have
	** taken information from those fields. I intend to keep the GifImageDesc data
	** structure as it is so that anyone needing the rest of the fields can do so 
	** quickly.
	*/

	if (EndianOrder == 1) /* LittleEndian */
	{
		GifImageDesc->ImageWidth  = (WORD) (GifImageDesc->GIDDump[4] & 0xFF);
		GifImageDesc->ImageWidth |= (WORD) ((GifImageDesc->GIDDump[5] & 0xFF) << 0x08);

		GifImageDesc->ImageHeight  = (WORD) (GifImageDesc->GIDDump[6] & 0xFF);
		GifImageDesc->ImageHeight |= (WORD) ((GifImageDesc->GIDDump[7] & 0xFF) << 0x08);

	}
	else
	{
		GifImageDesc->ImageWidth = (WORD) (GifImageDesc->GIDDump[4] & 0xFF);
		GifImageDesc->ImageWidth = ((WORD) (GifImageDesc->GIDDump[5] & 0xFF)) | (GifImageDesc->ImageWidth << 0x08);

		GifImageDesc->ImageHeight = (WORD) (GifImageDesc->GIDDump[6] & 0xFF);
		GifImageDesc->ImageHeight = ((WORD) (GifImageDesc->GIDDump[7] & 0xFF)) | (GifImageDesc->ImageWidth << 0x08);
		

	}
	
	GifImageDesc->PackedField = GifImageDesc->GIDDump[8];

	/* Interlace = GifImageDesc->PackedField & 0x20; */

    /* Check if a Local Color Table is present */
    if (GifImageDesc->PackedField & 0x80)
    {
        /* Read number of color table entries */
        tableSize = (WORD) (1L << ((GifImageDesc->PackedField & 0x07) + 1));
		GifImageDesc->TableSize = tableSize;
        /* Read the Local Color Table */
        for (i = 0; i < tableSize; i++)
        {
            GifImageDesc->HDFPalette[i][0] = *(*MemGif2)++;
            GifImageDesc->HDFPalette[i][1] = *(*MemGif2)++;
            GifImageDesc->HDFPalette[i][2] = *(*MemGif2)++;
        }
    }

	/*
	** Get LZW minimum Code Size
	*/
	GifImageDesc->CodeSize = (WORD)*(*MemGif2)++;

	/*GifImageDesc->GIFImage = ReadDataSubBlocks(FpGif);*/
	if (!(GifImageDesc->GIFImage = (BYTE *)malloc((GifImageDesc->ImageWidth) * (GifImageDesc->ImageHeight)))) {
		printf("Out of memory");
		exit(-1);
	}
	

	TempPtr = GifImageDesc->GIFImage;
	do
	{
		ch = ch1 = (int)*(*MemGif2)++;
		while (ch--) *TempPtr++ = *(*MemGif2)++;
	}
	while (ch1);


    return(0);          /* No FILE stream error occured */
}


/*
**  Read a GIF Graphic Control Extension block.
**
**  Note that the Introducer and Label field values in the GIFGRAPHICCONTROL
**  structure are assigned by the function calling ReadGifGraphicControl().
**
**  Returns: -1 if a FILE stream error occured during the read,
**           otherwise 0 if no error occured.
*/
int
ReadGifGraphicControl(GifGraphicControl, MemGif2)
GIFGRAPHICCONTROL *GifGraphicControl; /* Pointer to GC Extension structure */
BYTE              **MemGif2;          /* GIF image file input FILE stream  */
{

    
	for (i = 0 ; i < 5 ; i++) {
		GifGraphicControl->GCEDump[i] = *(*MemGif2)++;
	}

    return(0);          /* No FILE stream error occured */
}


/*
**  Read a GIF Plain Text Extension block.
**
**  Note that the Introducer and Label field values in the GIFLPLAINTEXT
**  structure are assigned by the function calling ReadGifPlainText().
**
**  Returns: -1 if a FILE stream error occured during the read,
**           otherwise 0 if no error occured.
*/
int
ReadGifPlainText(GifPlainText, MemGif2)
GIFPLAINTEXT *GifPlainText; /* Pointer to Plain Text Extension structure */
BYTE         **MemGif2;       /* GIF image file input FILE stream          */
{
	for (i = 0 ; i < 13 ; i++) {
		GifPlainText->PTEDump[i] = *(*MemGif2)++;
	}

    /* Read in the Plain Text data sub-blocks */
    if (!(GifPlainText->PlainTextData = ReadDataSubBlocks(MemGif2 , &(GifPlainText->DataSize))))
        return(1);

    /* 
	GifPlainText->Terminator       = 0;
	*/

    /* Check for a FILE stream error */
	/*
    if (ferror(FpGif))
        return(-1);
	*/

    return(0);          /* No FILE stream error occured */
}


/*
**  Read a GIF Application Extension block.
**
**  Note that the Introducer and Label field values in the GIFAPPLICATION
**  structure are assigned by the function calling ReadGifApplication().
**
**  Returns: -1 if a FILE stream error occured during the read,
**           otherwise 0 if no error occured.
*/
int
ReadGifApplication(GifApplication, MemGif2)
GIFAPPLICATION *GifApplication; /* Pointer to Application Extension structure */
BYTE           **MemGif2;          /* GIF image file input FILE stream           */
{
	for (i = 0 ; i < 12 ; i++) {
		GifApplication->AEDump[i] = *(*MemGif2)++;
	}

    /* Read in the Plain Text data sub-blocks */
    if (!(GifApplication->ApplicationData = ReadDataSubBlocks(MemGif2 , &(GifApplication->DataSize))))
        return(1);
	/*
    GifApplication->Terminator     = 0;
	*/
    
	/* Check for a FILE stream error */
	/*
    if (ferror(FpGif))
        return(-1);
	*/

    return(0);          /* No FILE stream error occured */
}


/*
**  Read a GIF Comment Extension block.
**
**  Note that the Introducer and Label field values in the GIFCOMMENT
**  structure are assigned by the function calling ReadGifComment().
**
**  Returns: -1 if a FILE stream error occured during the read,
**           otherwise 0 if no error occured.
*/
int
ReadGifComment(GifComment, MemGif2)
GIFCOMMENT *GifComment; /* Pointer to GIF Comment Extension structure */
BYTE       **MemGif2;      /* GIF image file input FILE stream           */
{
	
    /* Read in the Plain Text data sub-blocks */
    if (!(GifComment->CommentData = ReadDataSubBlocks(MemGif2 , &(GifComment->DataSize))))
        return(1);

    GifComment->Terminator = 0;
    
    return(0);          /* No FILE stream error occured */
}


/*
**  Read one or more GIF data sub-blocks and write the information
**  to a buffer.
**
**  A GIF "sub-block" is a single count byte followed by 1 to 255
**  additional data bytes.
**
**  Returns: A NULL pointer if a memory allocation error occured,
**           otherwise a valid pointer if no error occured.
*/
static BYTE *
ReadDataSubBlocks(MemGif2 , DSize)
BYTE **MemGif2;        /* GIF image file input FILE stream              */
WORD *DSize;
{
    BYTE *ptr1;     /* Pointer used to "walk the heap"               */
    BYTE *ptr2;     /* Pointer used to mark the top of the heap      */
    BYTE dataSize;  /* Size of the current data sub-block being read */
    WORD bufSize;   /* Total size of the Plain Text data buffer      */
	int tempcount = 0;

	bufSize = 0;				/* The output buffer is empty          */
	
    dataSize = *(*MemGif2)++;		/* Get the size of the first sub-block */
	
    /* Allocate initial data buffer */
    if (!(ptr1 = ptr2 = (BYTE *) malloc(dataSize + 1))) {
		printf("Out of memory. Allocation of memory for data sub-blocks for\neither Comment, Plain Text or Application Extensions failed");
        return((BYTE *) NULL);
	}
    for (;;)
    {
		tempcount++;
        bufSize += (dataSize);  /* Running total of the buffer size */
		*DSize = bufSize;

        /* *ptr1++ = dataSize;			/* Write the data count */
        while (dataSize--)			/* Read/write the Plain Text data */
             *ptr1++ = *(*MemGif2)++;
        
        /* Check if there is another data sub-block */
        if ((dataSize = *(*MemGif2)++) == 0)
            break;  /* Block Terminator encountered */
		
        /* Increase the buffer size to accomodate the next sub-block */
        if (!(ptr1 = ptr2 = (BYTE *) realloc(ptr2, bufSize + dataSize + 1)))
            return((BYTE *) NULL);
		

		ptr1 += bufSize;			/* Move pointer to the end of the data */
		
	
    }

    /**ptr1++ = (BYTE) NULL;			/* Add NULL to simulate Terminator value */
   	*ptr1++ = '\0';
	
    return(ptr2);					/* Return a pointer to the sub-block data */
}