1 /******************************************************************************
   2 
   3 gif_hash.h - magfic constants and declarations for GIF LZW
   4 
   5 ******************************************************************************/
   6 
   7 #ifndef _GIF_HASH_H_
   8 #define _GIF_HASH_H_
   9 
  10 #include <unistd.h>
  11 #include <stdint.h>
  12 
  13 #define HT_SIZE                 8192       /* 12bits = 4096 or twice as big! */
  14 #define HT_KEY_MASK             0x1FFF                        /* 13bits keys */
  15 #define HT_KEY_NUM_BITS         13                            /* 13bits keys */
  16 #define HT_MAX_KEY              8191    /* 13bits - 1, maximal code possible */
  17 #define HT_MAX_CODE             4095    /* Biggest code possible in 12 bits. */
  18 
  19 /* The 32 bits of the long are divided into two parts for the key & code:   */
  20 /* 1. The code is 12 bits as our compression algorithm is limited to 12bits */
  21 /* 2. The key is 12 bits Prefix code + 8 bit new char or 20 bits.           */
  22 /* The key is the upper 20 bits.  The code is the lower 12. */
  23 #define HT_GET_KEY(l)   (l >> 12)
  24 #define HT_GET_CODE(l)  (l & 0x0FFF)
  25 #define HT_PUT_KEY(l)   (l << 12)
  26 #define HT_PUT_CODE(l)  (l & 0x0FFF)
  27 
  28 typedef struct GifHashTableType {
  29     uint32_t HTable[HT_SIZE];
  30 } GifHashTableType;
  31 
  32 GifHashTableType *_InitHashTable(void);
  33 void _ClearHashTable(GifHashTableType *HashTable);
  34 void _InsertHashTable(GifHashTableType *HashTable, uint32_t Key, int Code);
  35 int _ExistsHashTable(GifHashTableType *HashTable, uint32_t Key);
  36 
  37 #endif /* _GIF_HASH_H_ */
  38 
  39 /* end */
--- EOF ---