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/* SPDX-License-Identifier: 0BSD */
/**
* \file lzma/vli.h
* \brief Variable-length integer handling
* \note Never include this file directly. Use <lzma.h> instead.
*
* 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
*/
#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
* underlying 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 a VLI or if it
* indicates an unknown value. False otherwise.
*/
#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[out] 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] out Beginning of the output buffer
* \param[out] 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[out] 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[out] 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[out] 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
*
* \param vli Integer whose encoded size is to be determined
*
* \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;
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