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 * underlying 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