www.pudn.com > Cimage.zip > GIFDECOD.H

/* DECODE.C - An LZW decoder for GIF 
 * Copyright (C) 1987, by Steven A. Bennett 
 * Copyright (C) 1994, C++ version by Alejandro Aguilar Sierra 
* 
 * Permission is given by the author to freely redistribute and include 
 * this code in any program as long as this credit is given where due. 
 * 
 * In accordance with the above, I want to credit Steve Wilhite who wrote 
 * the code which this is heavily inspired by... 
 * 
 * GIF and 'Graphics Interchange Format' are trademarks (tm) of 
 * Compuserve, Incorporated, an H&R Block Company. 
 * 
 * Release Notes: This file contains a decoder routine for GIF images 
 * which is similar, structurally, to the original routine by Steve Wilhite. 
 * It is, however, somewhat noticably faster in most cases. 
 * 
 */ 
 
#define LOCAL static 
#define FAST register 
 
typedef short SHORT;      				// 16 bits integer 
typedef unsigned short USHORT;		// 16 bits unsigned integer 
typedef unsigned char byte;             // 8 bits unsigned integer 
typedef unsigned long ULONG;            // 32 bits unsigned integer 
typedef int INT;                        // 16 bits integer 
 
#ifndef LONG 
typedef long LONG;                      // 32 bits integer 
#endif 
 
/* Various error codes used by decoder 
 */ 
#define OUT_OF_MEMORY -10 
#define BAD_CODE_SIZE -20 
#define READ_ERROR -1 
#define WRITE_ERROR -2 
#define OPEN_ERROR -3 
#define CREATE_ERROR -4 
#define NULL   0L 
#define MAX_CODES   4095 
 
class GIFDecoder 
{ 
protected: 
  SHORT init_exp(SHORT size); 
  SHORT get_next_code(); 
public: 
  SHORT decoder(SHORT linewidth, INT&  bad_code_count); 
/* bad_code_count is incremented each time an out of range code is read. 
 * When this value is non-zero after a decode, your GIF file is probably 
 * corrupt in some way... 
 */ 
 
  friend int get_byte(void); 
//   - This external (machine specific) function is expected to return 
// either the next byte from the GIF file, or a negative error number. 
 
 
friend int out_line(unsigned char *pixels, int linelen); 
/*   - This function takes a full line of pixels (one byte per pixel) and 
 * displays them (or does whatever your program wants with them...).  It 
 * should return zero, or negative if an error or some other event occurs 
 * which would require aborting the decode process...  Note that the length 
 * passed will almost always be equal to the line length passed to the 
 * decoder function, with the sole exception occurring when an ending code 
 * occurs in an odd place in the GIF file...  In any case, linelen will be 
 * equal to the number of pixels passed... 
*/ 
 
protected: 
/* Static variables */ 
SHORT curr_size;                     /* The current code size */ 
SHORT clear;                         /* Value for a clear code */ 
SHORT ending;                        /* Value for a ending code */ 
SHORT newcodes;                      /* First available code */ 
SHORT top_slot;                      /* Highest code for current size */ 
SHORT slot;                          /* Last read code */ 
 
/* The following static variables are used 
 * for seperating out codes 
 */ 
SHORT navail_bytes;              /* # bytes left in block */ 
SHORT nbits_left;                /* # bits left in current byte */ 
byte b1;                           /* Current byte */ 
byte byte_buff[257];               /* Current block */ 
byte *pbytes;                      /* Pointer to next byte in block */ 
};