lzw.h File Reference

The variable width LZW shared by the GIF and TIFF codecs. More...

#include <stddef.h>
#include <stdint.h>

Go to the source code of this file.

Classes
struct	TinyLzwTable
	The dictionary a stream builds as it is read. More...
struct	TinyLzwReader
	A code stream being read, in either bit order and framing. More...

Macros
#define	TINY_LZW_MAX_BITS   12u
#define	TINY_LZW_CODES   (1u << TINY_LZW_MAX_BITS)

Functions
void	tiny_lzw_init (TinyLzwReader *reader, const uint8_t *data, size_t size, size_t at, int chained, int msb)
	Points a reader at a stream.
int	tiny_lzw_expand (TinyLzwReader *reader, TinyLzwTable *table, uint32_t code_bits, int early, uint8_t *out, size_t capacity)
	Expands a stream into a byte plane.

Detailed Description

The variable width LZW shared by the GIF and TIFF codecs.

Author

Gregory Mitchell (me@gm.nosp@m.itch.nosp@m.215.x.nosp@m.yz)

Version

1.0.0

Date

2026-09-02

Copyright

Copyright (c) 2026

Macro Definition Documentation

TINY_LZW_CODES

#define TINY_LZW_CODES   (1u << TINY_LZW_MAX_BITS)

How many codes a dictionary can hold, which is all a twelve bit code names.

TINY_LZW_MAX_BITS

#define TINY_LZW_MAX_BITS   12u

Codes never exceed twelve bits in either format.

Function Documentation

tiny_lzw_expand()

int tiny_lzw_expand	(	TinyLzwReader *	reader,
		TinyLzwTable *	table,
		uint32_t	code_bits,
		int	early,
		uint8_t *	out,
		size_t	capacity )

Expands a stream into a byte plane.

Stops at the stream's end code, at the end of the buffer, or when the plane is full, whichever comes first. A stream that stops early leaves the rest of the plane as the caller filled it, which is what lets a truncated file decode the rows that did arrive.

Parameters

reader	The reader, positioned at the first code.
table	Scratch for the dictionary, which the caller owns.
code_bits	Root symbol width, so the first codes are one bit wider.
early	Non-zero to widen a code one entry early, which is TIFF's rule.
out	Destination plane.
capacity	How many bytes the plane holds.

Returns

int TINYIMG_OK, or TINYIMG_ERR_CORRUPT for a code the dictionary cannot explain.

tiny_lzw_init()

void tiny_lzw_init	(	TinyLzwReader *	reader,
		const uint8_t *	data,
		size_t	size,
		size_t	at,
		int	chained,
		int	msb )

Points a reader at a stream.

Parameters

reader	The reader.
data	The bytes.
size	Number of bytes.
at	Offset of the first code.
chained	Non-zero when the data is framed in sub-blocks.
msb	Non-zero to read most significant bit first.