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