TinyBitReader Struct Reference

Reads a bitstream out of a byte buffer. More...

#include <util.h>

Public Attributes
const uint8_t *	data
size_t	size
size_t	pos
uint32_t	accumulator
uint32_t	count
uint32_t	phantom
	How many of those bits came from past the end of the buffer.
int	overrun

Detailed Description

Reads a bitstream out of a byte buffer.

A stream is either most significant bit first (JPEG) or least significant bit first (DEFLATE, LZW, VP8L). One reader serves both, but a single stream must be read with one family of calls throughout; mixing them mid stream reads the accumulator in the wrong order.

Reading past the end yields zero bits and latches overrun, so a truncated file is detected once at the end of a scan rather than checked per symbol.

overrun means a read consumed bits that are not in the buffer, not merely that the accumulator refilled past the end. The two are different: the accumulator pulls whole bytes ahead of need, so decoding the last symbol of a stream that ends on a byte boundary refills past the end while every bit it uses is real. Latching on the refill instead reports a valid stream as truncated, which is what a bare DEFLATE stream with no trailer after it does.

Member Data Documentation

accumulator

uint32_t TinyBitReader::accumulator

Bits pulled but not yet consumed, an implementation detail.

count

uint32_t TinyBitReader::count

How many bits the accumulator holds, an implementation detail.

data

const uint8_t* TinyBitReader::data

The bytes being read.

overrun

int TinyBitReader::overrun

Set once a read has consumed bits that are not in the buffer.

phantom

uint32_t TinyBitReader::phantom

How many of those bits came from past the end of the buffer.

Always the newest bits, which both orders keep at the end reads reach last, so one comparison serves both. An implementation detail.

pos

size_t TinyBitReader::pos

Next byte to pull into the accumulator.

size

size_t TinyBitReader::size

How many bytes there are.

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The documentation for this struct was generated from the following file:

• /home/runner/work/tinyimg/tinyimg/include/tinyimg/util.h