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 */ 40