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40 lines
1.4 KiB
C
40 lines
1.4 KiB
C
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/******************************************************************************
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gif_hash.h - magfic constants and declarations for GIF LZW
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******************************************************************************/
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#ifndef _GIF_HASH_H_
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#define _GIF_HASH_H_
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#include <unistd.h>
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#include <stdint.h>
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#define HT_SIZE 8192 /* 12bits = 4096 or twice as big! */
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#define HT_KEY_MASK 0x1FFF /* 13bits keys */
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#define HT_KEY_NUM_BITS 13 /* 13bits keys */
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#define HT_MAX_KEY 8191 /* 13bits - 1, maximal code possible */
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#define HT_MAX_CODE 4095 /* Biggest code possible in 12 bits. */
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/* The 32 bits of the long are divided into two parts for the key & code: */
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/* 1. The code is 12 bits as our compression algorithm is limited to 12bits */
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/* 2. The key is 12 bits Prefix code + 8 bit new char or 20 bits. */
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/* The key is the upper 20 bits. The code is the lower 12. */
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#define HT_GET_KEY(l) (l >> 12)
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#define HT_GET_CODE(l) (l & 0x0FFF)
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#define HT_PUT_KEY(l) (l << 12)
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#define HT_PUT_CODE(l) (l & 0x0FFF)
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typedef struct GifHashTableType {
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uint32_t HTable[HT_SIZE];
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} GifHashTableType;
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GifHashTableType *_InitHashTable(void);
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void _ClearHashTable(GifHashTableType *HashTable);
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void _InsertHashTable(GifHashTableType *HashTable, uint32_t Key, int Code);
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int _ExistsHashTable(GifHashTableType *HashTable, uint32_t Key);
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#endif /* _GIF_HASH_H_ */
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/* end */
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