1 /****************************************************************************** 2 3 gif_hash.h - magfic constants and declarations for GIF LZW 4 5 SPDX-License-Identifier: MIT 6 7 ******************************************************************************/ 8 9 #ifndef _GIF_HASH_H_ 10 #define _GIF_HASH_H_ 11 12 #ifndef _WIN32 13 #include <unistd.h> 14 #endif /* _WIN32 */ 15 #include <stdint.h> 16 17 #define HT_SIZE 8192 /* 12bits = 4096 or twice as big! */ 18 #define HT_KEY_MASK 0x1FFF /* 13bits keys */ 19 #define HT_KEY_NUM_BITS 13 /* 13bits keys */ 20 #define HT_MAX_KEY 8191 /* 13bits - 1, maximal code possible */ 21 #define HT_MAX_CODE 4095 /* Biggest code possible in 12 bits. */ 22 23 /* The 32 bits of the long are divided into two parts for the key & code: */ 24 /* 1. The code is 12 bits as our compression algorithm is limited to 12bits */ 25 /* 2. The key is 12 bits Prefix code + 8 bit new char or 20 bits. */ 26 /* The key is the upper 20 bits. The code is the lower 12. */ 27 #define HT_GET_KEY(l) (l >> 12) 28 #define HT_GET_CODE(l) (l & 0x0FFF) 29 #define HT_PUT_KEY(l) (l << 12) 30 #define HT_PUT_CODE(l) (l & 0x0FFF) 31 32 typedef struct GifHashTableType { 33 uint32_t HTable[HT_SIZE]; 34 } GifHashTableType; 35 36 GifHashTableType *_InitHashTable(void); 37 void _ClearHashTable(GifHashTableType *HashTable); 38 void _InsertHashTable(GifHashTableType *HashTable, uint32_t Key, int Code); 39 int _ExistsHashTable(GifHashTableType *HashTable, uint32_t Key); 40 41 #endif /* _GIF_HASH_H_ */ 42 43 /* end */ 44