lib/inflate.bx

Read a DEFLATE stream, RFC 1951.

use "lib/inflate.bx";

What is in it

Name	Kind	What it answers
Inflater	class	at is the byte the next bits come from; bits/nbits hold what has been pulled off it and not yet consumed. A decode
inflate_bits	function	count bits, least significant first. A read past the end sets fault and answers 0 rather than trapping, because a tr
inflate_build	function	Build counts and symbols from a list of code lengths. Answers 0 for a complete code, a positive number for an incomp
inflate_decode	function	One symbol, most significant bit first. -1 on a code that is not in the tree.
inflate_tables	function	The same numbers lib/deflate.bx writes, read back. Duplicated rather than shared because the two modules are independe
inflate_codes	function	Decode literals and matches until the end-of-block symbol. A match may reach into bytes this call just wrote — a dis
inflate_fixed	function	—
inflate_dynamic	function	The one zlib actually writes. Three counts, then 19 code lengths in a permuted order, then the literal and distance
inflate_stored	function	BTYPE 00: the bit stream abandons its partial byte, then a length and its one’s complement.
inflate_into	function	A raw deflate stream starting at from. Answers how many bytes were written, or -1 for a stream this module refuses
zlib_into	function	A zlib stream — two header bytes and a trailing adler32 — which is what a PNG’s IDAT holds and what a ZIP entry does

Types

Inflater

class Inflater

at is the byte the next bits come from; bits/nbits hold what has been pulled off it and not yet consumed. A decoder is nothing but this plus two tables.

Source

Functions

inflate_bits

function inflate_bits(mutable state: Inflater, data: [Int], count: Int) -> Int

count bits, least significant first. A read past the end sets fault and answers 0 rather than trapping, because a truncated stream is a thing to report and not a thing to crash on: this module reads bytes somebody else wrote.

Source

inflate_build

function inflate_build(lengths: [Int], mutable counts: [Int], mutable symbols: [Int]) -> Int

Build counts and symbols from a list of code lengths. Answers 0 for a complete code, a positive number for an incomplete one, and -1 for over-subscribed — which is a malformed stream rather than a bug here, so it is a value and not a trap.

Source

inflate_decode

function inflate_decode(mutable state: Inflater, data: [Int], counts: [Int], symbols: [Int]) -> Int

One symbol, most significant bit first. -1 on a code that is not in the tree.

Source

inflate_tables

function inflate_tables(mutable length_base: [Int], mutable length_extra: [Int],

The same numbers lib/deflate.bx writes, read back. Duplicated rather than shared because the two modules are independent by design — and because a decoder importing the encoder to borrow a table would mean a program that only reads streams carries a compressor it never calls.

Source

inflate_codes

function inflate_codes(mutable state: Inflater, data: [Int], mutable out: [Int],

Decode literals and matches until the end-of-block symbol. A match may reach into bytes this call just wrote — a distance smaller than the length is legal and is how a run of one byte is encoded — so the copy is byte at a time from the growing output rather than a block move.

Source

inflate_fixed

function inflate_fixed(mutable state: Inflater, data: [Int], mutable out: [Int],

Source

inflate_dynamic

function inflate_dynamic(mutable state: Inflater, data: [Int], mutable out: [Int],

The one zlib actually writes. Three counts, then 19 code lengths in a permuted order, then the literal and distance lengths decoded with that tree — including three run-length symbols, one of which repeats the PREVIOUS length and therefore cannot be the first thing in the list.

Source

inflate_stored

function inflate_stored(mutable state: Inflater, data: [Int], mutable out: [Int]) -> Int

BTYPE 00: the bit stream abandons its partial byte, then a length and its one’s complement.

Source

inflate_into

function inflate_into(mutable out: [Int], data: [Int], from: Int) -> Int

A raw deflate stream starting at from. Answers how many bytes were written, or -1 for a stream this module refuses — truncated, over-subscribed, a distance past the start of the output, a reserved block type. A refusal is a value rather than a trap because these are somebody else’s bytes and a caller must be able to say “not this one” without dying.

Source

zlib_into

function zlib_into(mutable out: [Int], data: [Int]) -> Int

A zlib stream — two header bytes and a trailing adler32 — which is what a PNG’s IDAT holds and what a ZIP entry does NOT. The checksum is verified: a decoder that ignores it hands back bytes that failed their own check, which is the same defect as an oracle reading one copy of duplicated metadata.

Source