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/*
//
// gif.c
//
// GIF (Graphic Interchange Format) support functions
//
// Copyright (c) 1995-96 Jim Nelson. Permission to distribute
// granted by the author. No warranties are made on the fitness of this
// source code.
//
*/
#include "htp.h"
BOOL GifFormatFound(FILE *file)
{
BYTE header[8];
/* move to BOF */
if(fseek(file, 0, SEEK_SET) != 0)
{
DEBUG_PRINT(("unable to seek to start of GIF file"));
return FALSE;
}
/* read first six bytes, looking for GIF header + version info */
if(fread(header, 1, 6, file) != 6)
{
DEBUG_PRINT(("could not read GIF image file header"));
return FALSE;
}
/* is this a GIF file? */
if((memcmp(header, "GIF87a", 6) == 0) || (memcmp(header, "GIF89a", 6) == 0))
{
return TRUE;
}
/* not a GIF file */
return FALSE;
}
BOOL GifReadDimensions(FILE *file, WORD *height, WORD *width)
{
BYTE hi;
BYTE lo;
/* move to the image size position in the file header */
if(fseek(file, 6, SEEK_SET) != 0)
{
DEBUG_PRINT(("unable to seek to start of GIF file"));
return FALSE;
}
/* read the width, byte by byte */
/* this gets around machine endian problems while retaining the */
/* fact that GIF uses little-endian notation */
if(fread(&lo, 1, 1, file) != 1)
{
return FALSE;
}
if(fread(&hi, 1, 1, file) != 1)
{
return FALSE;
}
*width = MAKE_WORD(hi, lo);
/* read the height, byte by byte */
if(fread(&lo, 1, 1, file) != 1)
{
return FALSE;
}
if(fread(&hi, 1, 1, file) != 1)
{
return FALSE;
}
*height = MAKE_WORD(hi, lo);
return TRUE;
}
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