xz-utils (5.4.5)
1 /**
2 * \file lzma/vli.h
3 * \brief Variable-length integer handling
4 * \note Never include this file directly. Use <lzma.h> instead.
5 *
6 * In the .xz format, most integers are encoded in a variable-length
7 * representation, which is sometimes called little endian base-128 encoding.
8 * This saves space when smaller values are more likely than bigger values.
9 *
10 * The encoding scheme encodes seven bits to every byte, using minimum
11 * number of bytes required to represent the given value. Encodings that use
12 * non-minimum number of bytes are invalid, thus every integer has exactly
13 * one encoded representation. The maximum number of bits in a VLI is 63,
14 * thus the vli argument must be less than or equal to UINT64_MAX / 2. You
15 * should use LZMA_VLI_MAX for clarity.
16 */
17
18 /*
19 * Author: Lasse Collin
20 *
21 * This file has been put into the public domain.
22 * You can do whatever you want with this file.
23 */
24
25 #ifndef LZMA_H_INTERNAL
26 # error Never include this file directly. Use <lzma.h> instead.
27 #endif
28
29
30 /**
31 * \brief Maximum supported value of a variable-length integer
32 */
33 #define LZMA_VLI_MAX (UINT64_MAX / 2)
34
35 /**
36 * \brief VLI value to denote that the value is unknown
37 */
38 #define LZMA_VLI_UNKNOWN UINT64_MAX
39
40 /**
41 * \brief Maximum supported encoded length of variable length integers
42 */
43 #define LZMA_VLI_BYTES_MAX 9
44
45 /**
46 * \brief VLI constant suffix
47 */
48 #define LZMA_VLI_C(n) UINT64_C(n)
49
50
51 /**
52 * \brief Variable-length integer type
53 *
54 * Valid VLI values are in the range [0, LZMA_VLI_MAX]. Unknown value is
55 * indicated with LZMA_VLI_UNKNOWN, which is the maximum value of the
56 * underlying integer type.
57 *
58 * lzma_vli will be uint64_t for the foreseeable future. If a bigger size
59 * is needed in the future, it is guaranteed that 2 * LZMA_VLI_MAX will
60 * not overflow lzma_vli. This simplifies integer overflow detection.
61 */
62 typedef uint64_t lzma_vli;
63
64
65 /**
66 * \brief Validate a variable-length integer
67 *
68 * This is useful to test that application has given acceptable values
69 * for example in the uncompressed_size and compressed_size variables.
70 *
71 * \return True if the integer is representable as VLI or if it
72 * indicates unknown value. False if the integer cannot be
73 * represented as VLI.
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[out] 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] out Beginning of the output buffer
94 * \param[out] 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[out] 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[out] 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[out] 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 * \param vli Integer whose encoded size is to be determined
163 *
164 * \return Number of bytes on success (1-9). If vli isn't valid,
165 * zero is returned.
166 */
167 extern LZMA_API(uint32_t) lzma_vli_size(lzma_vli vli)
168 lzma_nothrow lzma_attr_pure;
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