rpnx::compression::lz4_codec Namespace Reference

Internal implementation of LZ4 frame compression and decompression. More...

Classes
class	xxhash32_accumulator
	Incremental XXH32 accumulator for streamed LZ4 content checksums. More...

Functions
std::uint32_t	rotate_left (std::uint32_t value, std::uint8_t count) noexcept
	Rotates a 32-bit value left without compiler-specific intrinsics.
std::uint32_t	read_word (std::span< std::byte const > input, std::size_t offset) noexcept
	Reads an unchecked little-endian word from a known-valid range.
std::uint32_t	xxhash32 (std::span< std::byte const > input, std::uint32_t seed=0U) noexcept
	Computes XXH32 as required by the LZ4 frame format.
void	append_extended_length (std::vector< std::byte > &output, std::size_t length)
	Encodes an extended LZ4 literal or match length.
std::vector< std::byte >	compress_block (std::span< std::byte const > input, std::int32_t level)
	Compresses one independent LZ4 block.
std::size_t	read_extended_length (std::span< std::byte const > input, std::size_t &position, std::size_t initial)
	Reads an LZ4 extended length while checking block bounds.
template<std::input_iterator input_iterator, std::sentinel_for< input_iterator > sentinel, typename output_iterator>
output_iterator	compress (input_iterator first, sentinel last, output_iterator output, compression_options const &options)
	Compresses an iterator range as an LZ4 frame.
template<std::input_iterator input_iterator, std::sentinel_for< input_iterator > sentinel, typename output_iterator>
output_iterator	decompress (input_iterator first, sentinel last, output_iterator output, decompression_options const &options)
	Decompresses one or more LZ4 frames.

Detailed Description

Internal implementation of LZ4 frame compression and decompression.

Function Documentation

append_extended_length()

void rpnx::compression::lz4_codec::append_extended_length ( std::vector< std::byte > & output, std::size_t length )

inline

Encodes an extended LZ4 literal or match length.

Parameters

output	Block buffer receiving extension bytes.
length	Amount beyond the token's base length.

Definition at line 185 of file lz4.hpp.

Referenced by compress_block().

compress()

template<std::input_iterator input_iterator, std::sentinel_for< input_iterator > sentinel, typename output_iterator>

output_iterator rpnx::compression::lz4_codec::compress	(	input_iterator	first,
		sentinel	last,
		output_iterator	output,
		compression_options const &	options )

Compresses an iterator range as an LZ4 frame.

Template Parameters

input_iterator	Single-pass byte iterator.
sentinel	Sentinel for first.
output_iterator	Destination byte iterator.

Parameters

first	First source byte.
last	Sentinel past the source.
output	Destination iterator.
options	Compression level from 0 through 12.

Returns

Destination advanced past the frame end mark.

Definition at line 336 of file lz4.hpp.

References compress_block(), rpnx::compression::invalid_option, rpnx::compression::compression_options::level, rpnx::compression::lz4_frame, rpnx::compression::implementation::to_byte(), rpnx::compression::implementation::write_byte(), and xxhash32().

compress_block()

std::vector< std::byte > rpnx::compression::lz4_codec::compress_block ( std::span< std::byte const > input, std::int32_t level )

inlinenodiscard

Compresses one independent LZ4 block.

Parameters

input	Uncompressed block containing at most 64 KiB.
level	Search level from 0 through 12.

Returns

Encoded block without an LZ4 frame header.

Definition at line 201 of file lz4.hpp.

References append_extended_length(), and read_word().

Referenced by compress().

decompress()

template<std::input_iterator input_iterator, std::sentinel_for< input_iterator > sentinel, typename output_iterator>

output_iterator rpnx::compression::lz4_codec::decompress	(	input_iterator	first,
		sentinel	last,
		output_iterator	output,
		decompression_options const &	options )

Decompresses one or more LZ4 frames.

Template Parameters

input_iterator	Single-pass byte iterator.
sentinel	Sentinel for first.
output_iterator	Destination byte iterator.

Parameters

first	First compressed byte.
last	Sentinel past the compressed input.
output	Destination iterator.
options	Output limit and concatenated-frame policy.

Returns

Destination advanced past the uncompressed data.

Definition at line 401 of file lz4.hpp.

References rpnx::compression::decompression_options::allow_concatenated_streams, rpnx::compression::implementation::byte_reader< input_iterator, sentinel >::empty(), rpnx::compression::invalid_data, rpnx::compression::lz4_frame, rpnx::compression::decompression_options::maximum_output_size, rpnx::compression::output_limit_exceeded, rpnx::compression::implementation::byte_reader< input_iterator, sentinel >::read(), read_extended_length(), rpnx::compression::trailing_data, rpnx::compression::unsupported_feature, rpnx::compression::lz4_codec::xxhash32_accumulator::update(), rpnx::compression::lz4_codec::xxhash32_accumulator::value(), rpnx::compression::implementation::write_byte(), and xxhash32().

read_extended_length()

std::size_t rpnx::compression::lz4_codec::read_extended_length ( std::span< std::byte const > input, std::size_t & position, std::size_t initial )

inlinenodiscard

Reads an LZ4 extended length while checking block bounds.

Parameters

input	Encoded block.
position	Current byte position, advanced past extension bytes.
initial	Length nibble from the token.

Returns

Complete literal or match length.

Exceptions

compression_error

If the extension is truncated or overflows size_t.

Definition at line 298 of file lz4.hpp.

References rpnx::compression::invalid_data, and rpnx::compression::lz4_frame.

Referenced by decompress().

read_word()

std::uint32_t rpnx::compression::lz4_codec::read_word ( std::span< std::byte const > input, std::size_t offset )

inlinenodiscardnoexcept

Reads an unchecked little-endian word from a known-valid range.

Parameters

input	Byte range containing at least four bytes at offset.
offset	Position of the first byte.

Returns

Decoded 32-bit word.

Definition at line 43 of file lz4.hpp.

Referenced by compress_block(), rpnx::compression::lz4_codec::xxhash32_accumulator::update(), rpnx::compression::lz4_codec::xxhash32_accumulator::value(), and xxhash32().

rotate_left()

std::uint32_t rpnx::compression::lz4_codec::rotate_left ( std::uint32_t value, std::uint8_t count )

inlinenodiscardnoexcept

Rotates a 32-bit value left without compiler-specific intrinsics.

Parameters

value	Value to rotate.
count	Rotation distance in the range 1–31.

Returns

Rotated value.

Definition at line 32 of file lz4.hpp.

Referenced by rpnx::compression::lz4_codec::xxhash32_accumulator::value(), and xxhash32().

xxhash32()

std::uint32_t rpnx::compression::lz4_codec::xxhash32 ( std::span< std::byte const > input, std::uint32_t seed = 0U )

inlinenodiscardnoexcept

Computes XXH32 as required by the LZ4 frame format.

Parameters

input	Bytes to hash.
seed	XXH32 seed.

Returns

Finalized 32-bit hash.

Definition at line 54 of file lz4.hpp.

References read_word(), and rotate_left().

Referenced by compress(), and decompress().