lzw.c File Reference

LZW decompression (implementation) More...

#include <assert.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdbool.h>
#include "lzw.h"

Include dependency graph for lzw.c:

Classes
struct	lzw_read_ctx
struct	lzw_table_entry
struct	lzw_ctx

Macros
#define	LZW_TABLE_ENTRY_MAX   (1u << LZW_CODE_MAX)

Typedefs
typedef uint32_t(*	lzw_writer_fn) (struct lzw_ctx *ctx, void *restrict output_data, uint32_t output_length, uint32_t output_pos, uint16_t code, uint16_t left)

Functions
lzw_result	lzw_context_create (struct lzw_ctx **ctx)
void	lzw_context_destroy (struct lzw_ctx *ctx)
lzw_result	lzw_decode_init (struct lzw_ctx *ctx, uint8_t minimum_code_size, const uint8_t *input_data, size_t input_length, size_t input_pos)
lzw_result	lzw_decode_init_map (struct lzw_ctx *ctx, uint8_t minimum_code_size, uint32_t transparency_idx, const uint32_t *colour_table, const uint8_t *input_data, size_t input_length, size_t input_pos)
lzw_result	lzw_decode (struct lzw_ctx *ctx, const uint8_t *restrict *const restrict output_data, uint32_t *restrict output_written)
lzw_result	lzw_decode_map (struct lzw_ctx *ctx, uint32_t *restrict output_data, uint32_t output_length, uint32_t *restrict output_written)

Detailed Description

LZW decompression (implementation)

Decoder for GIF LZW data.

Macro Definition Documentation

LZW_TABLE_ENTRY_MAX

#define LZW_TABLE_ENTRY_MAX   (1u << LZW_CODE_MAX)

Maximum number of lzw table entries.

Typedef Documentation

lzw_writer_fn

typedef uint32_t(* lzw_writer_fn) (struct lzw_ctx *ctx, void *restrict output_data, uint32_t output_length, uint32_t output_pos, uint16_t code, uint16_t left)

Function Documentation

lzw_context_create()

lzw_result lzw_context_create

(

struct lzw_ctx **

ctx

)

Create an LZW decompression context.

Parameters

[out]

ctx

Returns an LZW decompression context. Caller owned, free with lzw_context_destroy().

Returns

LZW_OK on success, or appropriate error code otherwise.

lzw_context_destroy()

void lzw_context_destroy

(

struct lzw_ctx *

ctx

)

Destroy an LZW decompression context.

Parameters

[in]

ctx

The LZW decompression context to destroy.

lzw_decode()

lzw_result lzw_decode	(	struct lzw_ctx *	ctx,
		const uint8_t *restrict *const restrict	output_data,
		uint32_t *restrict	output_written
	)

Read input codes until end of LZW context owned output buffer.

Ensure anything in output is used before calling this, as anything there before this call will be trampled.

Parameters

[in]	ctx	LZW reading context, updated.
[out]	output_data	Returns pointer to array of output values.
[out]	output_written	Returns the number of values written to data.

Returns

LZW_OK on success, or appropriate error code otherwise.

lzw_decode_init()

lzw_result lzw_decode_init	(	struct lzw_ctx *	ctx,
		uint8_t	minimum_code_size,
		const uint8_t *	input_data,
		size_t	input_length,
		size_t	input_pos
	)

Initialise an LZW decompression context for decoding.

Parameters

[in]	ctx	The LZW decompression context to initialise.
[in]	minimum_code_size	The LZW Minimum Code Size.
[in]	input_data	The compressed data.
[in]	input_length	Byte length of compressed data.
[in]	input_pos	Start position in data. Must be position of a size byte at sub-block start.

Returns

LZW_OK on success, or appropriate error code otherwise.

lzw_decode_init_map()

lzw_result lzw_decode_init_map	(	struct lzw_ctx *	ctx,
		uint8_t	minimum_code_size,
		uint32_t	transparency_idx,
		const uint32_t *	colour_table,
		const uint8_t *	input_data,
		size_t	input_length,
		size_t	input_pos
	)

Initialise an LZW decompression context for decoding to colour map values.

For transparency to work correctly, the given client buffer must have the values from the previous frame. The transparency_idx should be a value of 256 or above, if the frame does not have transparency.

Parameters

[in]	ctx	The LZW decompression context to initialise.
[in]	minimum_code_size	The LZW Minimum Code Size.
[in]	transparency_idx	Index representing transparency.
[in]	colour_table	Index to pixel colour mapping.
[in]	input_data	The compressed data.
[in]	input_length	Byte length of compressed data.
[in]	input_pos	Start position in data. Must be position of a size byte at sub-block start.

Returns

LZW_OK on success, or appropriate error code otherwise.

lzw_decode_map()

lzw_result lzw_decode_map	(	struct lzw_ctx *	ctx,
		uint32_t *restrict	output_data,
		uint32_t	output_length,
		uint32_t *restrict	output_written
	)

Read LZW codes into client buffer, mapping output to colours.

The context must have been initialised using lzw_decode_init_map before calling this function, in order to provide the colour mapping table and any transparency index.

Ensure anything in output is used before calling this, as anything there before this call will be trampled.

Parameters

[in]	ctx	LZW reading context, updated.
[in]	output_data	Client buffer to fill with colour mapped values.
[in]	output_length	Size of output array.
[out]	output_written	Returns the number of values written to data.

Returns

LZW_OK on success, or appropriate error code otherwise.