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lzma
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vli.h
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/** * \file lzma/vli.h * \brief Variable-length integer handling * * In the .xz format, most integers are encoded in a variable-length * representation, which is sometimes called little endian base-128 encoding. * This saves space when smaller values are more likely than bigger values. * * The encoding scheme encodes seven bits to every byte, using minimum * number of bytes required to represent the given value. Encodings that use * non-minimum number of bytes are invalid, thus every integer has exactly * one encoded representation. The maximum number of bits in a VLI is 63, * thus the vli argument must be less than or equal to UINT64_MAX / 2. You * should use LZMA_VLI_MAX for clarity. */ /* * Author: Lasse Collin * * This file has been put into the public domain. * You can do whatever you want with this file. * * See ../lzma.h for information about liblzma as a whole. */ #ifndef LZMA_H_INTERNAL # error Never include this file directly. Use <lzma.h> instead. #endif /** * \brief Maximum supported value of a variable-length integer */ #define LZMA_VLI_MAX (UINT64_MAX / 2) /** * \brief VLI value to denote that the value is unknown */ #define LZMA_VLI_UNKNOWN UINT64_MAX /** * \brief Maximum supported encoded length of variable length integers */ #define LZMA_VLI_BYTES_MAX 9 /** * \brief VLI constant suffix */ #define LZMA_VLI_C(n) UINT64_C(n) /** * \brief Variable-length integer type * * Valid VLI values are in the range [0, LZMA_VLI_MAX]. Unknown value is * indicated with LZMA_VLI_UNKNOWN, which is the maximum value of the * underlaying integer type. * * lzma_vli will be uint64_t for the foreseeable future. If a bigger size * is needed in the future, it is guaranteed that 2 * LZMA_VLI_MAX will * not overflow lzma_vli. This simplifies integer overflow detection. */ typedef uint64_t lzma_vli; /** * \brief Validate a variable-length integer * * This is useful to test that application has given acceptable values * for example in the uncompressed_size and compressed_size variables. * * \return True if the integer is representable as VLI or if it * indicates unknown value. */ #define lzma_vli_is_valid(vli) \ ((vli) <= LZMA_VLI_MAX || (vli) == LZMA_VLI_UNKNOWN) /** * \brief Encode a variable-length integer * * This function has two modes: single-call and multi-call. Single-call mode * encodes the whole integer at once; it is an error if the output buffer is * too small. Multi-call mode saves the position in *vli_pos, and thus it is * possible to continue encoding if the buffer becomes full before the whole * integer has been encoded. * * \param vli Integer to be encoded * \param vli_pos How many VLI-encoded bytes have already been written * out. When starting to encode a new integer in * multi-call mode, *vli_pos must be set to zero. * To use single-call encoding, set vli_pos to NULL. * \param out Beginning of the output buffer * \param out_pos The next byte will be written to out[*out_pos]. * \param out_size Size of the out buffer; the first byte into * which no data is written to is out[out_size]. * * \return Slightly different return values are used in multi-call and * single-call modes. * * Single-call (vli_pos == NULL): * - LZMA_OK: Integer successfully encoded. * - LZMA_PROG_ERROR: Arguments are not sane. This can be due * to too little output space; single-call mode doesn't use * LZMA_BUF_ERROR, since the application should have checked * the encoded size with lzma_vli_size(). * * Multi-call (vli_pos != NULL): * - LZMA_OK: So far all OK, but the integer is not * completely written out yet. * - LZMA_STREAM_END: Integer successfully encoded. * - LZMA_BUF_ERROR: No output space was provided. * - LZMA_PROG_ERROR: Arguments are not sane. */ extern LZMA_API(lzma_ret) lzma_vli_encode(lzma_vli vli, size_t *vli_pos, uint8_t *out, size_t *out_pos, size_t out_size) lzma_nothrow; /** * \brief Decode a variable-length integer * * Like lzma_vli_encode(), this function has single-call and multi-call modes. * * \param vli Pointer to decoded integer. The decoder will * initialize it to zero when *vli_pos == 0, so * application isn't required to initialize *vli. * \param vli_pos How many bytes have already been decoded. When * starting to decode a new integer in multi-call * mode, *vli_pos must be initialized to zero. To * use single-call decoding, set vli_pos to NULL. * \param in Beginning of the input buffer * \param in_pos The next byte will be read from in[*in_pos]. * \param in_size Size of the input buffer; the first byte that * won't be read is in[in_size]. * * \return Slightly different return values are used in multi-call and * single-call modes. * * Single-call (vli_pos == NULL): * - LZMA_OK: Integer successfully decoded. * - LZMA_DATA_ERROR: Integer is corrupt. This includes hitting * the end of the input buffer before the whole integer was * decoded; providing no input at all will use LZMA_DATA_ERROR. * - LZMA_PROG_ERROR: Arguments are not sane. * * Multi-call (vli_pos != NULL): * - LZMA_OK: So far all OK, but the integer is not * completely decoded yet. * - LZMA_STREAM_END: Integer successfully decoded. * - LZMA_DATA_ERROR: Integer is corrupt. * - LZMA_BUF_ERROR: No input was provided. * - LZMA_PROG_ERROR: Arguments are not sane. */ extern LZMA_API(lzma_ret) lzma_vli_decode(lzma_vli *vli, size_t *vli_pos, const uint8_t *in, size_t *in_pos, size_t in_size) lzma_nothrow; /** * \brief Get the number of bytes required to encode a VLI * * \return Number of bytes on success (1-9). If vli isn't valid, * zero is returned. */ extern LZMA_API(uint32_t) lzma_vli_size(lzma_vli vli) lzma_nothrow lzma_attr_pure;
