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