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