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gif_hash.h

/******************************************************************************
* Declarations, global to other of the GIF-HASH.C module.               *
*                                                           *
*                             Written by Gershon Elber,  Jun 1989   *
*******************************************************************************
* History:                                                  *
* 14 Jun 89 - Version 1.0 by Gershon Elber.                             *
******************************************************************************/

#define HT_SIZE               8192     /* 12bits = 4096 or twice as big! */
#define HT_KEY_MASK           0x1FFF                        /* 13bits keys */
#define HT_KEY_NUM_BITS       13                      /* 13bits keys */
#define HT_MAX_KEY            8191  /* 13bits - 1, maximal code possible */
#define HT_MAX_CODE           4095  /* Biggest code possible in 12 bits. */

/* The 32 bits of the long are divided into two parts for the key & code:   */
/* 1. The code is 12 bits as our compression algorithm is limited to 12bits */
/* 2. The key is 12 bits Prefix code + 8 bit new char or 20 bits.     */
#define HT_GET_KEY(l)   (l >> 12)
#define HT_GET_CODE(l)  (l & 0x0FFF)
#define HT_PUT_KEY(l)   (l << 12)
#define HT_PUT_CODE(l)  (l & 0x0FFF)

typedef struct GifHashTableType {
    unsigned long HTable[HT_SIZE];
} GifHashTableType;

GifHashTableType *_InitHashTable(void);
void _ClearHashTable(GifHashTableType *HashTable);
void _InsertHashTable(GifHashTableType *HashTable, unsigned long Key, int Code);
int _ExistsHashTable(GifHashTableType *HashTable, unsigned long Key);

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