1/* -*- mode: C; c-basic-offset: 4; indent-tabs-mode: nil -*- */
2// vim: expandtab:ts=8:sw=4:softtabstop=4:
3/**
4 * \file lzma/vli.h
5 * \brief Variable-length integer handling
6 *
7 * In the .xz format, most integers are encoded in a variable-length
8 * representation, which is sometimes called little endian base-128 encoding.
9 * This saves space when smaller values are more likely than bigger values.
10 *
11 * The encoding scheme encodes seven bits to every byte, using minimum
12 * number of bytes required to represent the given value. Encodings that use
13 * non-minimum number of bytes are invalid, thus every integer has exactly
14 * one encoded representation. The maximum number of bits in a VLI is 63,
15 * thus the vli argument must be at maximum of UINT64_MAX / 2. You should
16 * use LZMA_VLI_MAX for clarity.
17 */
18
19/*
20 * Author: Lasse Collin
21 *
22 * This file has been put into the public domain.
23 * You can do whatever you want with this file.
24 *
25 * See ../lzma.h for information about liblzma as a whole.
26 */
27
28#ifndef LZMA_H_INTERNAL
29# error Never include this file directly. Use <lzma.h> instead.
30#endif
31
32
33/**
34 * \brief Maximum supported value of variable-length integer
35 */
36#define LZMA_VLI_MAX (UINT64_MAX / 2)
37
38/**
39 * \brief VLI value to denote that the value is unknown
40 */
41#define LZMA_VLI_UNKNOWN UINT64_MAX
42
43/**
44 * \brief Maximum supported length of variable length integers
45 */
46#define LZMA_VLI_BYTES_MAX 9
47
48
49/**
50 * \brief VLI constant suffix
51 */
52#define LZMA_VLI_C(n) UINT64_C(n)
53
54
55/**
56 * \brief Variable-length integer type
57 *
58 * This will always be unsigned integer. Valid VLI values are in the range
59 * [0, LZMA_VLI_MAX]. Unknown value is indicated with LZMA_VLI_UNKNOWN,
60 * which is the maximum value of the underlaying integer type.
61 *
62 * In future, even if lzma_vli is typdefined to something else than uint64_t,
63 * it is guaranteed that 2 * LZMA_VLI_MAX will not overflow lzma_vli.
64 * This simplifies integer overflow detection.
65 */
66typedef uint64_t lzma_vli;
67
68
69/**
70 * \brief Simple macro to validate variable-length integer
71 *
72 * This is useful to test that application has given acceptable values
73 * for example in the uncompressed_size and compressed_size variables.
74 *
75 * \return True if the integer is representable as VLI or if it
76 * indicates unknown value.
77 */
78#define lzma_vli_is_valid(vli) \
79 ((vli) <= LZMA_VLI_MAX || (vli) == LZMA_VLI_UNKNOWN)
80
81
82/**
83 * \brief Encode a variable-length integer
84 *
85 * This function has two modes: single-call and multi-call. Single-call mode
86 * encodes the whole integer at once; it is an error if the output buffer is
87 * too small. Multi-call mode saves the position in *vli_pos, and thus it is
88 * possible to continue encoding if the buffer becomes full before the whole
89 * integer has been encoded.
90 *
91 * \param vli Integer to be encoded
92 * \param vli_pos How many VLI-encoded bytes have already been written
93 * out. When starting to encode a new integer, *vli_pos
94 * must be set to zero. To use single-call encoding,
95 * set vli_pos to NULL.
96 * \param out Beginning of the output buffer
97 * \param out_pos The next byte will be written to out[*out_pos].
98 * \param out_size Size of the out buffer; the first byte into
99 * which no data is written to is out[out_size].
100 *
101 * \return Slightly different return values are used in multi-call and
102 * single-call modes.
103 *
104 * Single-call (vli_pos == NULL):
105 * - LZMA_OK: Integer successfully encoded.
106 * - LZMA_PROG_ERROR: Arguments are not sane. This can be due
107 * to too little output space; single-call mode doesn't use
108 * LZMA_BUF_ERROR, since the application should have checked
109 * the encoded size with lzma_vli_size().
110 *
111 * Multi-call (vli_pos != NULL):
112 * - LZMA_OK: So far all OK, but the integer is not
113 * completely written out yet.
114 * - LZMA_STREAM_END: Integer successfully encoded.
115 * - LZMA_BUF_ERROR: No output space was provided.
116 * - LZMA_PROG_ERROR: Arguments are not sane.
117 */
118extern LZMA_API(lzma_ret) lzma_vli_encode(lzma_vli vli,
119 size_t *vli_pos, uint8_t *lzma_restrict out,
120 size_t *lzma_restrict out_pos, size_t out_size) lzma_nothrow;
121
122
123/**
124 * \brief Decode a variable-length integer
125 *
126 * Like lzma_vli_encode(), this function has single-call and multi-call modes.
127 *
128 * \param vli Pointer to decoded integer. The decoder will
129 * initialize it to zero when *vli_pos == 0, so
130 * application isn't required to initialize *vli.
131 * \param vli_pos How many bytes have already been decoded. When
132 * starting to decode a new integer, *vli_pos must
133 * be initialized to zero. To use single-call decoding,
134 * set this to NULL.
135 * \param in Beginning of the input buffer
136 * \param in_pos The next byte will be read from in[*in_pos].
137 * \param in_size Size of the input buffer; the first byte that
138 * won't be read is in[in_size].
139 *
140 * \return Slightly different return values are used in multi-call and
141 * single-call modes.
142 *
143 * Single-call (vli_pos == NULL):
144 * - LZMA_OK: Integer successfully decoded.
145 * - LZMA_DATA_ERROR: Integer is corrupt. This includes hitting
146 * the end of the input buffer before the whole integer was
147 * decoded; providing no input at all will use LZMA_DATA_ERROR.
148 * - LZMA_PROG_ERROR: Arguments are not sane.
149 *
150 * Multi-call (vli_pos != NULL):
151 * - LZMA_OK: So far all OK, but the integer is not
152 * completely decoded yet.
153 * - LZMA_STREAM_END: Integer successfully decoded.
154 * - LZMA_DATA_ERROR: Integer is corrupt.
155 * - LZMA_BUF_ERROR: No input was provided.
156 * - LZMA_PROG_ERROR: Arguments are not sane.
157 */
158extern LZMA_API(lzma_ret) lzma_vli_decode(lzma_vli *lzma_restrict vli,
159 size_t *vli_pos, const uint8_t *lzma_restrict in,
160 size_t *lzma_restrict in_pos, size_t in_size) lzma_nothrow;
161
162
163/**
164 * \brief Get the number of bytes required to encode a VLI
165 *
166 * \return Number of bytes on success (1-9). If vli isn't valid,
167 * zero is returned.
168 */
169extern LZMA_API(uint32_t) lzma_vli_size(lzma_vli vli)
170 lzma_nothrow lzma_attr_pure;
171