Compression API

CCSDS Section 5.3: Packet compression. More...

Data Structures
struct	ccsds124_compressor
	Compressor state structure. More...

Functions
int	ccsds124_compressor_init (ccsds124_compressor_t *comp, size_t F, const bitvector_t *initial_mask, uint8_t robustness, int pt_limit, int ft_limit, int rt_limit)
	Initialize compressor state.
void	ccsds124_compressor_reset (ccsds124_compressor_t *comp)
	Reset compressor to initial state.
int	ccsds124_compress_packet (ccsds124_compressor_t *comp, const bitvector_t *input, bitbuffer_t *output, const ccsds124_params_t *params)
	Compress a single input packet.
int	ccsds124_compress (ccsds124_compressor_t *comp, const uint8_t *input_data, size_t input_size, uint8_t *output_buffer, size_t output_buffer_size, size_t *output_size)
	Compress entire input data stream.
void	ccsds124_compute_robustness_window (bitvector_t *Xt, const ccsds124_compressor_t *comp, const bitvector_t *current_change)
	Compute robustness window Xₜ.
uint8_t	ccsds124_compute_effective_robustness (const ccsds124_compressor_t *comp, const bitvector_t *current_change)
	Compute effective robustness Vₜ.
int	ccsds124_has_positive_updates (const bitvector_t *Xt, const bitvector_t *mask)
	Check for positive mask updates (eₜ flag).
int	ccsds124_compute_ct_flag (const ccsds124_compressor_t *comp, uint8_t Vt, int current_new_mask_flag)
	Compute cₜ flag for multiple mask updates.

Detailed Description

CCSDS Section 5.3: Packet compression.

High-level compression interface for processing packets.

Function Documentation

ccsds124_compress()

int ccsds124_compress	(	ccsds124_compressor_t *	comp,
		const uint8_t *	input_data,
		size_t	input_size,
		uint8_t *	output_buffer,
		size_t	output_buffer_size,
		size_t *	output_size
	)

Compress entire input data stream.

High-level API that handles:

• Splitting input into F-bit packets
• Automatic ṗₜ/ḟₜ/ṙₜ parameter management
• CCSDS init phase (first Rₜ+1 packets)
• Output accumulation with byte padding

Parameters

[in,out]	comp	Compressor state (must be initialized)
[in]	input_data	Raw input byte array
[in]	input_size	Input size in bytes (multiple of F/8)
[out]	output_buffer	Output buffer (caller-allocated)
[in]	output_buffer_size	Size of output buffer
[out]	output_size	Actual bytes written

Returns

CCSDS124_OK on success, error code otherwise

Definition at line 518 of file compress.c.

References bitbuffer_init(), bitbuffer_to_bytes(), bitvector_from_bytes(), bitvector_init(), ccsds124_compress_packet(), ccsds124_compressor_reset(), CCSDS124_ERROR_INVALID_ARG, CCSDS124_ERROR_OVERFLOW, CCSDS124_MAX_OUTPUT_BYTES, CCSDS124_OK, ccsds124_compressor::F, ccsds124_compressor::ft_counter, ccsds124_compressor::ft_limit, ccsds124_params_t::min_robustness, ccsds124_params_t::new_mask_flag, ccsds124_compressor::pt_counter, ccsds124_compressor::pt_limit, ccsds124_compressor::robustness, ccsds124_compressor::rt_counter, ccsds124_compressor::rt_limit, ccsds124_params_t::send_mask_flag, and ccsds124_params_t::uncompressed_flag.

Referenced by do_compress().

ccsds124_compress_packet()

int ccsds124_compress_packet	(	ccsds124_compressor_t *	comp,
		const bitvector_t *	input,
		bitbuffer_t *	output,
		const ccsds124_params_t *	params
	)

Compress a single input packet.

Compresses one F-bit packet according to CCSDS 124.0-B-1 Section 5.3. Updates compressor state for next packet.

Parameters

[in,out]	comp	Compressor state (updated in place)
[in]	input	Input packet Iₜ (must be length F)
[out]	output	Compressed output buffer
[in]	params	Compression parameters (NULL = use automatic)

Returns

CCSDS124_OK on success, error code otherwise

Definition at line 330 of file compress.c.

References bitbuffer_append_bit(), bitbuffer_append_bitvector(), bitbuffer_clear(), bitvector_copy(), bitvector_hamming_weight(), bitvector_left_shift(), bitvector_not(), bitvector_or(), bitvector_xor(), ccsds124_compressor::build, ccsds124_bit_extract(), ccsds124_bit_extract_forward(), ccsds124_compute_change(), ccsds124_compute_ct_flag(), ccsds124_compute_effective_robustness(), ccsds124_compute_robustness_window(), ccsds124_count_encode(), CCSDS124_ERROR_INVALID_ARG, ccsds124_has_positive_updates(), CCSDS124_MAX_HISTORY, CCSDS124_MAX_VT_HISTORY, CCSDS124_OK, ccsds124_rle_encode(), ccsds124_update_build(), ccsds124_update_mask(), ccsds124_compressor::change_history, ccsds124_compressor::F, ccsds124_compressor::flag_history_index, get_default_params(), ccsds124_compressor::history_index, bitvector::length, ccsds124_compressor::mask, ccsds124_params_t::new_mask_flag, ccsds124_compressor::new_mask_flag_history, ccsds124_compressor::prev_input, ccsds124_compressor::prev_mask, ccsds124_params_t::send_mask_flag, ccsds124_compressor::t, ccsds124_params_t::uncompressed_flag, ccsds124_compressor::work_change, ccsds124_compressor::work_diff, ccsds124_compressor::work_inverted, ccsds124_compressor::work_prev_build, ccsds124_compressor::work_shifted, and ccsds124_compressor::work_Xt.

Referenced by ccsds124_compress().

ccsds124_compressor_init()

int ccsds124_compressor_init	(	ccsds124_compressor_t *	comp,
		size_t	F,
		const bitvector_t *	initial_mask,
		uint8_t	robustness,
		int	pt_limit,
		int	ft_limit,
		int	rt_limit
	)

Initialize compressor state.

Sets up the compressor for a new compression session. Use pt_limit/ft_limit/rt_limit > 0 for automatic parameter management, or 0 to control parameters manually via ccsds124_params_t.

Parameters

[out]	comp	Compressor to initialize (caller-allocated)
[in]	F	Input vector length in bits
[in]	initial_mask	M₀ initial mask (NULL = all zeros)
[in]	robustness	Rₜ base robustness level (0-7)
[in]	pt_limit	New mask period (0 = manual control)
[in]	ft_limit	Send mask period (0 = manual control)
[in]	rt_limit	Uncompressed period (0 = manual control)

Returns

CCSDS124_OK on success, error code otherwise

Definition at line 36 of file compress.c.

References bitvector_copy(), bitvector_init(), bitvector_zero(), ccsds124_compressor::build, ccsds124_compressor_reset(), CCSDS124_ERROR_INVALID_ARG, CCSDS124_MAX_HISTORY, CCSDS124_MAX_PACKET_LENGTH, CCSDS124_MAX_ROBUSTNESS, CCSDS124_MAX_VT_HISTORY, CCSDS124_OK, ccsds124_compressor::change_history, ccsds124_compressor::F, ccsds124_compressor::flag_history_index, ccsds124_compressor::ft_limit, ccsds124_compressor::initial_mask, ccsds124_compressor::mask, ccsds124_compressor::new_mask_flag_history, ccsds124_compressor::prev_input, ccsds124_compressor::prev_mask, ccsds124_compressor::pt_limit, ccsds124_compressor::robustness, ccsds124_compressor::rt_limit, ccsds124_compressor::work_change, ccsds124_compressor::work_diff, ccsds124_compressor::work_inverted, ccsds124_compressor::work_prev_build, ccsds124_compressor::work_shifted, and ccsds124_compressor::work_Xt.

Referenced by do_compress().

ccsds124_compressor_reset()

void ccsds124_compressor_reset

(

ccsds124_compressor_t *

comp

)

Reset compressor to initial state.

Resets time index to 0 and clears all history while preserving configuration (F, robustness, limits).

Parameters

[out]

comp

Compressor to reset

Definition at line 107 of file compress.c.

References bitvector_copy(), bitvector_zero(), ccsds124_compressor::build, CCSDS124_MAX_HISTORY, ccsds124_compressor::change_history, ccsds124_compressor::ft_counter, ccsds124_compressor::ft_limit, ccsds124_compressor::history_index, ccsds124_compressor::initial_mask, ccsds124_compressor::mask, ccsds124_compressor::prev_input, ccsds124_compressor::prev_mask, ccsds124_compressor::pt_counter, ccsds124_compressor::pt_limit, ccsds124_compressor::rt_counter, ccsds124_compressor::rt_limit, and ccsds124_compressor::t.

Referenced by ccsds124_compress(), and ccsds124_compressor_init().

ccsds124_compute_ct_flag()

int ccsds124_compute_ct_flag	(	const ccsds124_compressor_t *	comp,
		uint8_t	Vt,
		int	current_new_mask_flag
	)

Compute cₜ flag for multiple mask updates.

Returns 1 if ṗₜ was set 2+ times in the last Vₜ iterations, indicating the kₜ component is needed in output.

Parameters

[in]	comp	Compressor with flag history
[in]	Vt	Effective robustness level
[in]	current_new_mask_flag	Current packet's ṗₜ value

Returns

1 if multiple updates, 0 otherwise

Definition at line 282 of file compress.c.

References CCSDS124_MAX_VT_HISTORY, ccsds124_compressor::flag_history_index, ccsds124_compressor::new_mask_flag_history, and ccsds124_compressor::t.

Referenced by ccsds124_compress_packet().

ccsds124_compute_effective_robustness()

uint8_t ccsds124_compute_effective_robustness	(	const ccsds124_compressor_t *	comp,
		const bitvector_t *	current_change
	)

Compute effective robustness Vₜ.

Calculates Vₜ = Rₜ + Cₜ where Cₜ counts consecutive iterations without mask changes.

Parameters

[in]	comp	Compressor with change history
[in]	current_change	Current change vector Dₜ

Returns

Effective robustness Vₜ (0-15)

Definition at line 210 of file compress.c.

References bitvector_hamming_weight(), CCSDS124_MAX_HISTORY, ccsds124_compressor::change_history, ccsds124_compressor::history_index, ccsds124_compressor::robustness, and ccsds124_compressor::t.

Referenced by ccsds124_compress_packet().

ccsds124_compute_robustness_window()

void ccsds124_compute_robustness_window	(	bitvector_t *	Xt,
		const ccsds124_compressor_t *	comp,
		const bitvector_t *	current_change
	)

Compute robustness window Xₜ.

Computes the OR of recent change vectors for robustness encoding: Xₜ = <(Dₜ₋ᴿₜ OR ... OR Dₜ)> where denotes bit reversal.

Parameters

[out]	Xt	Robustness window (reversed for RLE)
[in]	comp	Compressor with change history
[in]	current_change	Current change vector Dₜ

Definition at line 173 of file compress.c.

References bitvector_copy(), CCSDS124_MAX_HISTORY, ccsds124_compressor::change_history, bitvector::data, ccsds124_compressor::F, ccsds124_compressor::history_index, bitvector::length, bitvector::num_words, ccsds124_compressor::robustness, and ccsds124_compressor::t.

Referenced by ccsds124_compress_packet().

ccsds124_has_positive_updates()

int ccsds124_has_positive_updates	(	const bitvector_t *	Xt,
		const bitvector_t *	mask
	)

Check for positive mask updates (eₜ flag).

Determines if any changed bits in Xₜ are predictable (have mask bit = 0), indicating positive updates.

Parameters

[in]	Xt	Robustness window (reversed)
[in]	mask	Current mask Mₜ

Returns

1 if positive updates exist, 0 otherwise

Definition at line 254 of file compress.c.

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

Referenced by ccsds124_compress_packet().