1 | /** |
2 | * \file lzma/vli.h |
3 | * \brief Variable-length integer handling |
4 | * |
5 | * In the .xz format, most integers are encoded in a variable-length |
6 | * representation, which is sometimes called little endian base-128 encoding. |
7 | * This saves space when smaller values are more likely than bigger values. |
8 | * |
9 | * The encoding scheme encodes seven bits to every byte, using minimum |
10 | * number of bytes required to represent the given value. Encodings that use |
11 | * non-minimum number of bytes are invalid, thus every integer has exactly |
12 | * one encoded representation. The maximum number of bits in a VLI is 63, |
13 | * thus the vli argument must be less than or equal to UINT64_MAX / 2. You |
14 | * should use LZMA_VLI_MAX for clarity. |
15 | */ |
16 | |
17 | /* |
18 | * Author: Lasse Collin |
19 | * |
20 | * This file has been put into the public domain. |
21 | * You can do whatever you want with this file. |
22 | * |
23 | * See ../lzma.h for information about liblzma as a whole. |
24 | */ |
25 | |
26 | #ifndef LZMA_H_INTERNAL |
27 | # error Never include this file directly. Use <lzma.h> instead. |
28 | #endif |
29 | |
30 | |
31 | /** |
32 | * \brief Maximum supported value of a variable-length integer |
33 | */ |
34 | #define LZMA_VLI_MAX (UINT64_MAX / 2) |
35 | |
36 | /** |
37 | * \brief VLI value to denote that the value is unknown |
38 | */ |
39 | #define LZMA_VLI_UNKNOWN UINT64_MAX |
40 | |
41 | /** |
42 | * \brief Maximum supported encoded length of variable length integers |
43 | */ |
44 | #define LZMA_VLI_BYTES_MAX 9 |
45 | |
46 | /** |
47 | * \brief VLI constant suffix |
48 | */ |
49 | #define LZMA_VLI_C(n) UINT64_C(n) |
50 | |
51 | |
52 | /** |
53 | * \brief Variable-length integer type |
54 | * |
55 | * Valid VLI values are in the range [0, LZMA_VLI_MAX]. Unknown value is |
56 | * indicated with LZMA_VLI_UNKNOWN, which is the maximum value of the |
57 | * underlaying integer type. |
58 | * |
59 | * lzma_vli will be uint64_t for the foreseeable future. If a bigger size |
60 | * is needed in the future, it is guaranteed that 2 * LZMA_VLI_MAX will |
61 | * not overflow lzma_vli. This simplifies integer overflow detection. |
62 | */ |
63 | typedef uint64_t lzma_vli; |
64 | |
65 | |
66 | /** |
67 | * \brief Validate a variable-length integer |
68 | * |
69 | * This is useful to test that application has given acceptable values |
70 | * for example in the uncompressed_size and compressed_size variables. |
71 | * |
72 | * \return True if the integer is representable as VLI or if it |
73 | * indicates unknown value. |
74 | */ |
75 | #define lzma_vli_is_valid(vli) \ |
76 | ((vli) <= LZMA_VLI_MAX || (vli) == LZMA_VLI_UNKNOWN) |
77 | |
78 | |
79 | /** |
80 | * \brief Encode a variable-length integer |
81 | * |
82 | * This function has two modes: single-call and multi-call. Single-call mode |
83 | * encodes the whole integer at once; it is an error if the output buffer is |
84 | * too small. Multi-call mode saves the position in *vli_pos, and thus it is |
85 | * possible to continue encoding if the buffer becomes full before the whole |
86 | * integer has been encoded. |
87 | * |
88 | * \param vli Integer to be encoded |
89 | * \param vli_pos How many VLI-encoded bytes have already been written |
90 | * out. When starting to encode a new integer in |
91 | * multi-call mode, *vli_pos must be set to zero. |
92 | * To use single-call encoding, set vli_pos to NULL. |
93 | * \param out Beginning of the output buffer |
94 | * \param out_pos The next byte will be written to out[*out_pos]. |
95 | * \param out_size Size of the out buffer; the first byte into |
96 | * which no data is written to is out[out_size]. |
97 | * |
98 | * \return Slightly different return values are used in multi-call and |
99 | * single-call modes. |
100 | * |
101 | * Single-call (vli_pos == NULL): |
102 | * - LZMA_OK: Integer successfully encoded. |
103 | * - LZMA_PROG_ERROR: Arguments are not sane. This can be due |
104 | * to too little output space; single-call mode doesn't use |
105 | * LZMA_BUF_ERROR, since the application should have checked |
106 | * the encoded size with lzma_vli_size(). |
107 | * |
108 | * Multi-call (vli_pos != NULL): |
109 | * - LZMA_OK: So far all OK, but the integer is not |
110 | * completely written out yet. |
111 | * - LZMA_STREAM_END: Integer successfully encoded. |
112 | * - LZMA_BUF_ERROR: No output space was provided. |
113 | * - LZMA_PROG_ERROR: Arguments are not sane. |
114 | */ |
115 | extern LZMA_API(lzma_ret) lzma_vli_encode(lzma_vli vli, size_t *vli_pos, |
116 | uint8_t *out, size_t *out_pos, size_t out_size) lzma_nothrow; |
117 | |
118 | |
119 | /** |
120 | * \brief Decode a variable-length integer |
121 | * |
122 | * Like lzma_vli_encode(), this function has single-call and multi-call modes. |
123 | * |
124 | * \param vli Pointer to decoded integer. The decoder will |
125 | * initialize it to zero when *vli_pos == 0, so |
126 | * application isn't required to initialize *vli. |
127 | * \param vli_pos How many bytes have already been decoded. When |
128 | * starting to decode a new integer in multi-call |
129 | * mode, *vli_pos must be initialized to zero. To |
130 | * use single-call decoding, set vli_pos to NULL. |
131 | * \param in Beginning of the input buffer |
132 | * \param in_pos The next byte will be read from in[*in_pos]. |
133 | * \param in_size Size of the input buffer; the first byte that |
134 | * won't be read is in[in_size]. |
135 | * |
136 | * \return Slightly different return values are used in multi-call and |
137 | * single-call modes. |
138 | * |
139 | * Single-call (vli_pos == NULL): |
140 | * - LZMA_OK: Integer successfully decoded. |
141 | * - LZMA_DATA_ERROR: Integer is corrupt. This includes hitting |
142 | * the end of the input buffer before the whole integer was |
143 | * decoded; providing no input at all will use LZMA_DATA_ERROR. |
144 | * - LZMA_PROG_ERROR: Arguments are not sane. |
145 | * |
146 | * Multi-call (vli_pos != NULL): |
147 | * - LZMA_OK: So far all OK, but the integer is not |
148 | * completely decoded yet. |
149 | * - LZMA_STREAM_END: Integer successfully decoded. |
150 | * - LZMA_DATA_ERROR: Integer is corrupt. |
151 | * - LZMA_BUF_ERROR: No input was provided. |
152 | * - LZMA_PROG_ERROR: Arguments are not sane. |
153 | */ |
154 | extern LZMA_API(lzma_ret) lzma_vli_decode(lzma_vli *vli, size_t *vli_pos, |
155 | const uint8_t *in, size_t *in_pos, size_t in_size) |
156 | lzma_nothrow; |
157 | |
158 | |
159 | /** |
160 | * \brief Get the number of bytes required to encode a VLI |
161 | * |
162 | * \return Number of bytes on success (1-9). If vli isn't valid, |
163 | * zero is returned. |
164 | */ |
165 | extern LZMA_API(uint32_t) lzma_vli_size(lzma_vli vli) |
166 | lzma_nothrow lzma_attr_pure; |
167 | |