4 * Constants for the LZX compression format.
7 #ifndef _LZX_CONSTANTS_H
8 #define _LZX_CONSTANTS_H
10 /* Number of literal byte values. */
11 #define LZX_NUM_CHARS 256
13 /* The smallest and largest allowed match lengths. */
14 #define LZX_MIN_MATCH_LEN 2
15 #define LZX_MAX_MATCH_LEN 257
17 /* Number of distinct match lengths that can be represented. */
18 #define LZX_NUM_LENS (LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1)
20 /* Number of match lengths for which no length symbol is required. */
21 #define LZX_NUM_PRIMARY_LENS 7
22 #define LZX_NUM_LEN_HEADERS (LZX_NUM_PRIMARY_LENS + 1)
24 /* The first length which requires a length symbol. */
25 #define LZX_MIN_SECONDARY_LEN (LZX_MIN_MATCH_LEN + LZX_NUM_PRIMARY_LENS)
27 /* Valid values of the 3-bit block type field. */
28 #define LZX_BLOCKTYPE_VERBATIM 1
29 #define LZX_BLOCKTYPE_ALIGNED 2
30 #define LZX_BLOCKTYPE_UNCOMPRESSED 3
32 /* 'LZX_MIN_WINDOW_SIZE' and 'LZX_MAX_WINDOW_SIZE' are the minimum and maximum
33 * sizes of the sliding window. */
34 #define LZX_MIN_WINDOW_ORDER 15
35 #define LZX_MAX_WINDOW_ORDER 21
36 #define LZX_MIN_WINDOW_SIZE (1UL << LZX_MIN_WINDOW_ORDER) /* 32768 */
37 #define LZX_MAX_WINDOW_SIZE (1UL << LZX_MAX_WINDOW_ORDER) /* 2097152 */
39 /* Maximum number of offset slots. (The actual number of offset slots depends
40 * on the window size.) */
41 #define LZX_MAX_OFFSET_SLOTS 50
43 /* Maximum number of symbols in the main code. (The actual number of symbols in
44 * the main code depends on the window size.) */
45 #define LZX_MAINCODE_MAX_NUM_SYMBOLS \
46 (LZX_NUM_CHARS + (LZX_MAX_OFFSET_SLOTS * LZX_NUM_LEN_HEADERS))
48 /* Number of symbols in the length code. */
49 #define LZX_LENCODE_NUM_SYMBOLS (LZX_NUM_LENS - LZX_NUM_PRIMARY_LENS)
51 /* Number of symbols in the pre-code. */
52 #define LZX_PRECODE_NUM_SYMBOLS 20
54 /* Number of bits in which each pre-code codeword length is represented. */
55 #define LZX_PRECODE_ELEMENT_SIZE 4
57 /* Number of low-order bits of each match offset that are entropy-encoded in
58 * aligned offset blocks. */
59 #define LZX_NUM_ALIGNED_OFFSET_BITS 3
61 /* Number of symbols in the aligned offset code. */
62 #define LZX_ALIGNEDCODE_NUM_SYMBOLS (1 << LZX_NUM_ALIGNED_OFFSET_BITS)
64 /* Mask for the match offset bits that are entropy-encoded in aligned offset
66 #define LZX_ALIGNED_OFFSET_BITMASK ((1 << LZX_NUM_ALIGNED_OFFSET_BITS) - 1)
68 /* Number of bits in which each aligned offset codeword length is represented. */
69 #define LZX_ALIGNEDCODE_ELEMENT_SIZE 3
71 /* The first offset slot which requires an aligned offset symbol in aligned
73 #define LZX_MIN_ALIGNED_OFFSET_SLOT 8
75 /* The offset slot base for LZX_MIN_ALIGNED_OFFSET_SLOT. */
76 #define LZX_MIN_ALIGNED_OFFSET 14
78 /* The maximum number of extra offset bits in verbatim blocks. (One would need
79 * to subtract LZX_NUM_ALIGNED_OFFSET_BITS to get the number of extra offset
80 * bits in *aligned* blocks.) */
81 #define LZX_MAX_NUM_EXTRA_BITS 17
83 /* Maximum lengths (in bits) for length-limited Huffman code construction. */
84 #define LZX_MAX_MAIN_CODEWORD_LEN 16
85 #define LZX_MAX_LEN_CODEWORD_LEN 16
86 #define LZX_MAX_PRE_CODEWORD_LEN ((1 << LZX_PRECODE_ELEMENT_SIZE) - 1)
87 #define LZX_MAX_ALIGNED_CODEWORD_LEN ((1 << LZX_ALIGNEDCODE_ELEMENT_SIZE) - 1)
89 /* For LZX-compressed blocks in WIM resources, this value is always used as the
90 * filesize parameter for the call instruction (0xe8 byte) preprocessing, even
91 * though the blocks themselves are not this size, and the size of the actual
92 * file resource in the WIM file is very likely to be something entirely
93 * different as well. */
94 #define LZX_WIM_MAGIC_FILESIZE 12000000
96 /* Assumed LZX block size when the encoded block size begins with a 0 bit.
97 * This is probably WIM-specific. */
98 #define LZX_DEFAULT_BLOCK_SIZE 32768
100 /* Number of offsets in the recent (or "repeat") offsets queue. */
101 #define LZX_NUM_RECENT_OFFSETS 3
103 /* An offset of n bytes is actually encoded as (n + LZX_OFFSET_ADJUSTMENT). */
104 #define LZX_OFFSET_ADJUSTMENT (LZX_NUM_RECENT_OFFSETS - 1)
106 #endif /* _LZX_CONSTANTS_H */