decompress.c File Reference

CCSDS 124.0-B-1 decompression algorithm implementation. More...

#include "ccsds124.h"
#include <string.h>

Go to the source code of this file.

Data Structures
struct	ccsds124_decompress_flags_t
	Internal flags extracted during decompression. More...

Functions
Internal Helper Functions
Implements CCSDS 124.0-B-1 decompression (inverse of Section 5.3): Bit reader for parsing compressed packets COUNT and RLE decoding Packet decompression and mask reconstruction Code follows MISRA C:2012 guidelines. Authors Georges Labrèche georg.nosp@m.es@t.nosp@m.anagr.nosp@m.aspa.nosp@m.ce.co.nosp@m.m — https://georges.fyi Claude Code (Anthropic) norep.nosp@m.ly@a.nosp@m.nthro.nosp@m.pic..nosp@m.com See also https://ccsds.org/Pubs/124x0b1.pdf CCSDS 124.0-B-1 Standard
static size_t	bitvector_get_set_positions (const bitvector_t *bv, size_t *positions, size_t max_pos)
	Extract positions of all set bits in a bitvector using word-level processing.
Bit Reader Functions
void	bitreader_init (bitreader_t *reader, const uint8_t *data, size_t num_bits)
	Initialize bit reader.
int	bitreader_read_bit (bitreader_t *reader)
	Read a single bit.
uint32_t	bitreader_read_bits (bitreader_t *reader, size_t num_bits)
	Read multiple bits as unsigned value.
size_t	bitreader_position (const bitreader_t *reader)
	Get current bit position.
size_t	bitreader_remaining (const bitreader_t *reader)
	Get remaining bits.
void	bitreader_align_byte (bitreader_t *reader)
	Skip to next byte boundary.
Decoding Functions
int	ccsds124_count_decode (bitreader_t *reader, uint32_t *value)
	Counter decoding (inverse of ccsds124_count_encode).
int	ccsds124_rle_decode (bitreader_t *reader, bitvector_t *result, size_t length)
	Run-length decoding (inverse of ccsds124_rle_encode).
int	ccsds124_bit_insert (bitreader_t *reader, bitvector_t *data, const bitvector_t *mask)
	Bit insertion (inverse of ccsds124_bit_extract).
Decompressor Initialization
int	ccsds124_decompressor_init (ccsds124_decompressor_t *decomp, size_t F, const bitvector_t *initial_mask, uint8_t robustness)
	Initialize decompressor state.
void	ccsds124_decompressor_reset (ccsds124_decompressor_t *decomp)
	Reset decompressor to initial state.
int	ccsds124_decompressor_notify_packet_loss (ccsds124_decompressor_t *decomp, uint32_t lost_count)
	Notify decompressor of packet loss.
Packet Decompression
static int	ccsds124_decompress_packet_internal (ccsds124_decompressor_t *decomp, bitreader_t *reader, bitvector_t *output, ccsds124_decompress_flags_t *flags)
	Internal decompression with optional flag extraction.
int	ccsds124_decompress_packet (ccsds124_decompressor_t *decomp, bitreader_t *reader, bitvector_t *output)
	Decompress a single compressed packet.
int	ccsds124_decompress_packet_checked (ccsds124_decompressor_t *decomp, const uint8_t *data, size_t num_bits, bitvector_t *output, ccsds124_decompress_result_t *result)
	Decompress a single packet with accuracy guarantee checking.
static int	skip_rle_sequence_span (bitreader_t *reader, uint32_t *hamming_weight, uint64_t *span)
	Skip COUNT values in an RLE sequence until the terminator.
int	ccsds124_discover_packet_length (const uint8_t *data, size_t num_bits, uint32_t *packet_length)
	Discover packet length (F) from a compressed packet.
int	ccsds124_decompress (ccsds124_decompressor_t *decomp, const uint8_t *input_data, size_t input_size, uint8_t *output_buffer, size_t output_buffer_size, size_t *output_size)
	Decompress entire compressed data stream.

Detailed Description

CCSDS 124.0-B-1 decompression algorithm implementation.

Definition in file decompress.c.

Function Documentation

bitvector_get_set_positions()

static size_t bitvector_get_set_positions ( const bitvector_t *  bv, size_t *  positions, size_t  max_pos  )

static

Extract positions of all set bits in a bitvector using word-level processing.

Much faster than iterating bit-by-bit when the bitvector is sparse. Uses __builtin_clz for O(1) MSB position finding.

Parameters

[in]	bv	Bitvector to scan
[out]	positions	Array to store positions (must be at least hamming_weight elements)
[in]	max_pos	Maximum positions to extract

Returns

Number of positions extracted

Definition at line 48 of file decompress.c.

References bitvector::data, and bitvector::num_words.

Referenced by ccsds124_bit_insert(), and ccsds124_decompress_packet_internal().

ccsds124_decompress_packet_internal()

static int ccsds124_decompress_packet_internal ( ccsds124_decompressor_t *  decomp, bitreader_t *  reader, bitvector_t *  output, ccsds124_decompress_flags_t *  flags  )

static

Internal decompression with optional flag extraction.

Core decompression logic shared by both ccsds124_decompress_packet() and ccsds124_decompress_packet_checked().

Parameters

[in,out]	decomp	Decompressor state
[in,out]	reader	Bit reader
[out]	output	Decompressed output
[out]	flags	Optional extracted flags (NULL to skip)

Returns

CCSDS124_OK or negative error code

Definition at line 491 of file decompress.c.

References bitreader_read_bit(), bitreader_read_bits(), bitreader_remaining(), bitvector_copy(), bitvector_equals(), bitvector_get_bit(), bitvector_get_set_positions(), bitvector_hamming_weight(), bitvector_init(), bitvector_or(), bitvector_set_bit(), bitvector_zero(), ccsds124_bit_insert(), ccsds124_count_decode(), CCSDS124_ERROR_INVALID_ARG, CCSDS124_ERROR_UNDERFLOW, CCSDS124_MAX_PACKET_LENGTH, CCSDS124_OK, ccsds124_rle_decode(), ccsds124_decompressor::count_f_mismatch, ccsds124_decompressor::F, ccsds124_decompress_flags_t::ft, ccsds124_decompressor::mask, ccsds124_decompressor::mask_inconsistent, ccsds124_decompressor::prev_output, ccsds124_decompress_flags_t::rt, ccsds124_decompressor::t, ccsds124_decompress_flags_t::Vt, and ccsds124_decompressor::Xt.

Referenced by ccsds124_decompress_packet(), and ccsds124_decompress_packet_checked().

skip_rle_sequence_span()

static int skip_rle_sequence_span ( bitreader_t *  reader, uint32_t *  hamming_weight, uint64_t *  span  )

static

Skip COUNT values in an RLE sequence until the terminator.

Reads and discards COUNT values from the reader until a terminator (COUNT value 0) is found. Returns the hamming weight (number of non-terminator values decoded) via output parameter.

Parameters

[in,out]	reader	Bit reader
[out]	hamming_weight	Number of non-terminator COUNTs decoded

Returns

CCSDS124_OK on success, error code on decode failure

Skip an RLE-encoded sequence, tracking hamming weight and span.

The span is the sum of all RLE deltas, which equals one plus the highest '1' position encoded. An RLE sequence for a vector of length F must have span <= F — a larger span means the h or q vector is inconsistent with F (cross-validation rule v1.6).

Parameters

[in,out]	reader	Bit reader
[out]	hamming_weight	Number of non-terminator COUNTs decoded
[out]	span	Sum of decoded deltas (1 + highest position)

Returns

CCSDS124_OK on success, error code on decode failure

Definition at line 932 of file decompress.c.

References ccsds124_count_decode(), and CCSDS124_OK.

Referenced by ccsds124_discover_packet_length().