3 * \brief Variable-length integer handling
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.
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.
18 * Author: Lasse Collin
20 * This file has been put into the public domain.
21 * You can do whatever you want with this file.
23 * See ../lzma.h for information about liblzma as a whole.
26 #ifndef LZMA_H_INTERNAL
27 # error Never include this file directly. Use <lzma.h> instead.
32 * \brief Maximum supported value of variable-length integer
34 #define LZMA_VLI_MAX (UINT64_MAX / 2)
37 * \brief VLI value to denote that the value is unknown
39 #define LZMA_VLI_UNKNOWN UINT64_MAX
42 * \brief Maximum supported length of variable length integers
44 #define LZMA_VLI_BYTES_MAX 9
48 * \brief VLI constant suffix
50 #define LZMA_VLI_C(n) UINT64_C(n)
54 * \brief Variable-length integer type
56 * This will always be unsigned integer. Valid VLI values are in the range
57 * [0, LZMA_VLI_MAX]. Unknown value is indicated with LZMA_VLI_UNKNOWN,
58 * which is the maximum value of the underlaying integer type.
60 * In future, even if lzma_vli is defined to be something other than uint64_t,
61 * it is guaranteed that 2 * LZMA_VLI_MAX will not overflow lzma_vli.
62 * This simplifies integer overflow detection.
64 typedef uint64_t lzma_vli;
68 * \brief Simple macro to validate variable-length integer
70 * This is useful to test that application has given acceptable values
71 * for example in the uncompressed_size and compressed_size variables.
73 * \return True if the integer is representable as VLI or if it
74 * indicates unknown value.
76 #define lzma_vli_is_valid(vli) \
77 ((vli) <= LZMA_VLI_MAX || (vli) == LZMA_VLI_UNKNOWN)
81 * \brief Encode a variable-length integer
83 * This function has two modes: single-call and multi-call. Single-call mode
84 * encodes the whole integer at once; it is an error if the output buffer is
85 * too small. Multi-call mode saves the position in *vli_pos, and thus it is
86 * possible to continue encoding if the buffer becomes full before the whole
87 * integer has been encoded.
89 * \param vli Integer to be encoded
90 * \param vli_pos How many VLI-encoded bytes have already been written
91 * out. When starting to encode a new integer, *vli_pos
92 * must be set to zero. To use single-call encoding,
93 * set vli_pos to NULL.
94 * \param out Beginning of the output buffer
95 * \param out_pos The next byte will be written to out[*out_pos].
96 * \param out_size Size of the out buffer; the first byte into
97 * which no data is written to is out[out_size].
99 * \return Slightly different return values are used in multi-call and
102 * Single-call (vli_pos == NULL):
103 * - LZMA_OK: Integer successfully encoded.
104 * - LZMA_PROG_ERROR: Arguments are not sane. This can be due
105 * to too little output space; single-call mode doesn't use
106 * LZMA_BUF_ERROR, since the application should have checked
107 * the encoded size with lzma_vli_size().
109 * Multi-call (vli_pos != NULL):
110 * - LZMA_OK: So far all OK, but the integer is not
111 * completely written out yet.
112 * - LZMA_STREAM_END: Integer successfully encoded.
113 * - LZMA_BUF_ERROR: No output space was provided.
114 * - LZMA_PROG_ERROR: Arguments are not sane.
116 extern LZMA_API(lzma_ret) lzma_vli_encode(lzma_vli vli,
117 size_t *vli_pos, uint8_t *lzma_restrict out,
118 size_t *lzma_restrict out_pos, size_t out_size) lzma_nothrow;
122 * \brief Decode a variable-length integer
124 * Like lzma_vli_encode(), this function has single-call and multi-call modes.
126 * \param vli Pointer to decoded integer. The decoder will
127 * initialize it to zero when *vli_pos == 0, so
128 * application isn't required to initialize *vli.
129 * \param vli_pos How many bytes have already been decoded. When
130 * starting to decode a new integer, *vli_pos must
131 * be initialized to zero. To use single-call decoding,
133 * \param in Beginning of the input buffer
134 * \param in_pos The next byte will be read from in[*in_pos].
135 * \param in_size Size of the input buffer; the first byte that
136 * won't be read is in[in_size].
138 * \return Slightly different return values are used in multi-call and
141 * Single-call (vli_pos == NULL):
142 * - LZMA_OK: Integer successfully decoded.
143 * - LZMA_DATA_ERROR: Integer is corrupt. This includes hitting
144 * the end of the input buffer before the whole integer was
145 * decoded; providing no input at all will use LZMA_DATA_ERROR.
146 * - LZMA_PROG_ERROR: Arguments are not sane.
148 * Multi-call (vli_pos != NULL):
149 * - LZMA_OK: So far all OK, but the integer is not
150 * completely decoded yet.
151 * - LZMA_STREAM_END: Integer successfully decoded.
152 * - LZMA_DATA_ERROR: Integer is corrupt.
153 * - LZMA_BUF_ERROR: No input was provided.
154 * - LZMA_PROG_ERROR: Arguments are not sane.
156 extern LZMA_API(lzma_ret) lzma_vli_decode(lzma_vli *lzma_restrict vli,
157 size_t *vli_pos, const uint8_t *lzma_restrict in,
158 size_t *lzma_restrict in_pos, size_t in_size) lzma_nothrow;
162 * \brief Get the number of bytes required to encode a VLI
164 * \return Number of bytes on success (1-9). If vli isn't valid,
167 extern LZMA_API(uint32_t) lzma_vli_size(lzma_vli vli)
168 lzma_nothrow lzma_attr_pure;