Compressed resource data in 'dcmp' (1) format,
as stored in compressed resources with header type 8 and decompressor ID 1.
The 'dcmp' (1) decompressor resource is included in the System file of System 7.0 and later.
This compression format is used for a few compressed resources in System 7.0's files
(such as the Finder Help file).
This decompressor is also included with and used by some other Apple applications,
such as ResEdit.
(Note: ResEdit includes the 'dcmp' (1) resource,
but none of its resources actually use this decompressor.)
This compression format supports some basic general-purpose compression schemes, including backreferences to previous data and run-length encoding. It also includes some types of compression tailored specifically to Mac OS resources, including a set of single-byte codes that correspond to entries in a hard-coded lookup table.
The 'dcmp' (0) compression format (see dcmp_0.ksy) is very similar to this format,
with the main difference that it operates mostly on units of 2 or 4 bytes.
This makes the ``dcmp' (0)format more suitable for word-aligned data, such as executable code, bitmaps, sounds, etc. The'dcmp' (0)` format also appears to be generally preferred over `'dcmp' (1)`,
with the latter only being used in resource files that contain mostly unaligned data,
such as text.
This page hosts a formal specification of Compressed Macintosh resource data, Apple `'dcmp' (1)` format using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
<?php
// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
/**
* Compressed resource data in `'dcmp' (1)` format,
* as stored in compressed resources with header type `8` and decompressor ID `1`.
*
* The `'dcmp' (1)` decompressor resource is included in the System file of System 7.0 and later.
* This compression format is used for a few compressed resources in System 7.0's files
* (such as the Finder Help file).
* This decompressor is also included with and used by some other Apple applications,
* such as ResEdit.
* (Note: ResEdit includes the `'dcmp' (1)` resource,
* but none of its resources actually use this decompressor.)
*
* This compression format supports some basic general-purpose compression schemes,
* including backreferences to previous data and run-length encoding.
* It also includes some types of compression tailored specifically to Mac OS resources,
* including a set of single-byte codes that correspond to entries in a hard-coded lookup table.
*
* The `'dcmp' (0)` compression format (see dcmp_0.ksy) is very similar to this format,
* with the main difference that it operates mostly on units of 2 or 4 bytes.
* This makes the ``dcmp' (0)` format more suitable for word-aligned data,
* such as executable code, bitmaps, sounds, etc.
* The `'dcmp' (0)` format also appears to be generally preferred over `'dcmp' (1)`,
* with the latter only being used in resource files that contain mostly unaligned data,
* such as text.
*/
namespace {
class Dcmp1 extends \Kaitai\Struct\Struct {
public function __construct(\Kaitai\Struct\Stream $_io, \Kaitai\Struct\Struct $_parent = null, \Dcmp1 $_root = null) {
parent::__construct($_io, $_parent, $_root);
$this->_read();
}
private function _read() {
$this->_m_chunks = [];
$i = 0;
do {
$_ = new \Dcmp1\Chunk($this->_io, $this, $this->_root);
$this->_m_chunks[] = $_;
$i++;
} while (!($_->tag() == 255));
}
protected $_m_chunks;
/**
* The sequence of chunks that make up the compressed data.
*/
public function chunks() { return $this->_m_chunks; }
}
}
/**
* A single chunk of compressed data.
* Each chunk in the compressed data expands to a sequence of bytes in the uncompressed data,
* except when `tag == 0xff`,
* which marks the end of the data and does not correspond to any bytes in the uncompressed data.
*
* Most chunks are stateless and always expand to the same data,
* regardless of where the chunk appears in the sequence.
* However,
* some chunks affect the behavior of future chunks,
* or expand to different data depending on which chunks came before them.
*/
namespace Dcmp1 {
class Chunk extends \Kaitai\Struct\Struct {
public function __construct(\Kaitai\Struct\Stream $_io, \Dcmp1 $_parent = null, \Dcmp1 $_root = null) {
parent::__construct($_io, $_parent, $_root);
$this->_read();
}
private function _read() {
$this->_m_tag = $this->_io->readU1();
switch (( (($this->tag() >= 0) && ($this->tag() <= 31)) ? \Dcmp1\Chunk\TagKind::LITERAL : ( (($this->tag() >= 32) && ($this->tag() <= 207)) ? \Dcmp1\Chunk\TagKind::BACKREFERENCE : ( (($this->tag() >= 208) && ($this->tag() <= 209)) ? \Dcmp1\Chunk\TagKind::LITERAL : ($this->tag() == 210 ? \Dcmp1\Chunk\TagKind::BACKREFERENCE : ( (($this->tag() >= 213) && ($this->tag() <= 253)) ? \Dcmp1\Chunk\TagKind::TABLE_LOOKUP : ($this->tag() == 254 ? \Dcmp1\Chunk\TagKind::EXTENDED : ($this->tag() == 255 ? \Dcmp1\Chunk\TagKind::END : \Dcmp1\Chunk\TagKind::INVALID)))))))) {
case \Dcmp1\Chunk\TagKind::EXTENDED:
$this->_m_body = new \Dcmp1\Chunk\ExtendedBody($this->_io, $this, $this->_root);
break;
case \Dcmp1\Chunk\TagKind::LITERAL:
$this->_m_body = new \Dcmp1\Chunk\LiteralBody($this->tag(), $this->_io, $this, $this->_root);
break;
case \Dcmp1\Chunk\TagKind::END:
$this->_m_body = new \Dcmp1\Chunk\EndBody($this->_io, $this, $this->_root);
break;
case \Dcmp1\Chunk\TagKind::TABLE_LOOKUP:
$this->_m_body = new \Dcmp1\Chunk\TableLookupBody($this->tag(), $this->_io, $this, $this->_root);
break;
case \Dcmp1\Chunk\TagKind::BACKREFERENCE:
$this->_m_body = new \Dcmp1\Chunk\BackreferenceBody($this->tag(), $this->_io, $this, $this->_root);
break;
}
}
protected $_m_tag;
protected $_m_body;
/**
* The chunk's tag byte.
* This controls the structure of the body and the meaning of the chunk.
*/
public function tag() { return $this->_m_tag; }
/**
* The chunk's body.
*
* Certain chunks do not have any data following the tag byte.
* In this case,
* the body is a zero-length structure.
*/
public function body() { return $this->_m_body; }
}
}
/**
* The body of a literal data chunk.
*
* The data that this chunk expands to is stored literally in the body (`literal`).
* Optionally,
* the literal data may also be stored for use by future backreference chunks (`do_store`).
*/
namespace Dcmp1\Chunk {
class LiteralBody extends \Kaitai\Struct\Struct {
public function __construct(int $tag, \Kaitai\Struct\Stream $_io, \Dcmp1\Chunk $_parent = null, \Dcmp1 $_root = null) {
parent::__construct($_io, $_parent, $_root);
$this->_m_tag = $tag;
$this->_read();
}
private function _read() {
if ($this->isLenLiteralSeparate()) {
$this->_m_lenLiteralSeparate = $this->_io->readU1();
}
$this->_m_literal = $this->_io->readBytes($this->lenLiteral());
}
protected $_m_doStore;
/**
* Whether this literal should be stored for use by future backreference chunks.
*
* See the documentation of the `backreference_body` type for details about backreference chunks.
*/
public function doStore() {
if ($this->_m_doStore !== null)
return $this->_m_doStore;
$this->_m_doStore = ($this->isLenLiteralSeparate() ? $this->tag() == 209 : ($this->tag() & 16) != 0);
return $this->_m_doStore;
}
protected $_m_lenLiteralM1InTag;
/**
* The part of the tag byte that indicates the length of the literal data,
* in bytes,
* minus one.
*
* If the tag byte is 0xd0 or 0xd1,
* the length is stored in a separate byte after the tag byte and before the literal data.
*/
public function lenLiteralM1InTag() {
if ($this->_m_lenLiteralM1InTag !== null)
return $this->_m_lenLiteralM1InTag;
if (!($this->isLenLiteralSeparate())) {
$this->_m_lenLiteralM1InTag = ($this->tag() & 15);
}
return $this->_m_lenLiteralM1InTag;
}
protected $_m_isLenLiteralSeparate;
/**
* Whether the length of the literal is stored separately from the tag.
*/
public function isLenLiteralSeparate() {
if ($this->_m_isLenLiteralSeparate !== null)
return $this->_m_isLenLiteralSeparate;
$this->_m_isLenLiteralSeparate = $this->tag() >= 208;
return $this->_m_isLenLiteralSeparate;
}
protected $_m_lenLiteral;
/**
* The length of the literal data,
* in bytes.
*
* In practice,
* this value is always greater than zero,
* as there is no use in storing a zero-length literal.
*/
public function lenLiteral() {
if ($this->_m_lenLiteral !== null)
return $this->_m_lenLiteral;
$this->_m_lenLiteral = ($this->isLenLiteralSeparate() ? $this->lenLiteralSeparate() : ($this->lenLiteralM1InTag() + 1));
return $this->_m_lenLiteral;
}
protected $_m_lenLiteralSeparate;
protected $_m_literal;
protected $_m_tag;
/**
* The length of the literal data,
* in bytes.
*
* This field is only present if the tag byte is 0xd0 or 0xd1.
* In practice,
* this only happens if the length is 0x11 or greater,
* because smaller lengths can be encoded into the tag byte.
*/
public function lenLiteralSeparate() { return $this->_m_lenLiteralSeparate; }
/**
* The literal data.
*/
public function literal() { return $this->_m_literal; }
/**
* The tag byte preceding this chunk body.
*/
public function tag() { return $this->_m_tag; }
}
}
/**
* The body of a backreference chunk.
*
* This chunk expands to the data stored in a preceding literal chunk,
* indicated by an index number (`index`).
*/
namespace Dcmp1\Chunk {
class BackreferenceBody extends \Kaitai\Struct\Struct {
public function __construct(int $tag, \Kaitai\Struct\Stream $_io, \Dcmp1\Chunk $_parent = null, \Dcmp1 $_root = null) {
parent::__construct($_io, $_parent, $_root);
$this->_m_tag = $tag;
$this->_read();
}
private function _read() {
if ($this->isIndexSeparate()) {
$this->_m_indexSeparateMinus = $this->_io->readU1();
}
}
protected $_m_isIndexSeparate;
/**
* Whether the index is stored separately from the tag.
*/
public function isIndexSeparate() {
if ($this->_m_isIndexSeparate !== null)
return $this->_m_isIndexSeparate;
$this->_m_isIndexSeparate = $this->tag() == 210;
return $this->_m_isIndexSeparate;
}
protected $_m_indexInTag;
/**
* The index of the referenced literal chunk,
* as stored in the tag byte.
*/
public function indexInTag() {
if ($this->_m_indexInTag !== null)
return $this->_m_indexInTag;
$this->_m_indexInTag = ($this->tag() - 32);
return $this->_m_indexInTag;
}
protected $_m_indexSeparate;
/**
* The index of the referenced literal chunk,
* as stored separately from the tag byte,
* with the implicit offset corrected for.
*/
public function indexSeparate() {
if ($this->_m_indexSeparate !== null)
return $this->_m_indexSeparate;
if ($this->isIndexSeparate()) {
$this->_m_indexSeparate = ($this->indexSeparateMinus() + 176);
}
return $this->_m_indexSeparate;
}
protected $_m_index;
/**
* The index of the referenced literal chunk.
*
* Stored literals are assigned index numbers in the order in which they appear in the compressed data,
* starting at 0.
* Non-stored literals are not counted in the numbering and cannot be referenced using backreferences.
* Once an index is assigned to a stored literal,
* it is never changed or unassigned for the entire length of the compressed data.
*
* As the name indicates,
* a backreference can only reference stored literal chunks found *before* the backreference,
* not ones that come after it.
*/
public function index() {
if ($this->_m_index !== null)
return $this->_m_index;
$this->_m_index = ($this->isIndexSeparate() ? $this->indexSeparate() : $this->indexInTag());
return $this->_m_index;
}
protected $_m_indexSeparateMinus;
protected $_m_tag;
/**
* The index of the referenced literal chunk,
* stored separately from the tag.
* The value in this field is stored minus 0xb0.
*
* This field is only present if the tag byte is 0xd2.
* For other tag bytes,
* the index is encoded in the tag byte.
* Values smaller than 0xb0 cannot be stored in this field,
* they must always be encoded in the tag byte.
*/
public function indexSeparateMinus() { return $this->_m_indexSeparateMinus; }
/**
* The tag byte preceding this chunk body.
*/
public function tag() { return $this->_m_tag; }
}
}
/**
* The body of a table lookup chunk.
* This body is always empty.
*
* This chunk always expands to two bytes (`value`),
* determined from the tag byte using a fixed lookup table (`lookup_table`).
* This lookup table is hardcoded in the decompressor and always the same for all compressed data.
*/
namespace Dcmp1\Chunk {
class TableLookupBody extends \Kaitai\Struct\Struct {
public function __construct(int $tag, \Kaitai\Struct\Stream $_io, \Dcmp1\Chunk $_parent = null, \Dcmp1 $_root = null) {
parent::__construct($_io, $_parent, $_root);
$this->_m_tag = $tag;
$this->_read();
}
private function _read() {
}
protected $_m_lookupTable;
/**
* Fixed lookup table that maps tag byte numbers to two bytes each.
*
* The entries in the lookup table are offset -
* index 0 stands for tag 0xd5, 1 for 0xd6, etc.
*/
public function lookupTable() {
if ($this->_m_lookupTable !== null)
return $this->_m_lookupTable;
$this->_m_lookupTable = ["\x00\x00", "\x00\x01", "\x00\x02", "\x00\x03", "\x2E\x01", "\x3E\x01", "\x01\x01", "\x1E\x01", "\xFF\xFF", "\x0E\x01", "\x31\x00", "\x11\x12", "\x01\x07", "\x33\x32", "\x12\x39", "\xED\x10", "\x01\x27", "\x23\x22", "\x01\x37", "\x07\x06", "\x01\x17", "\x01\x23", "\x00\xFF", "\x00\x2F", "\x07\x0E", "\xFD\x3C", "\x01\x35", "\x01\x15", "\x01\x02", "\x00\x07", "\x00\x3E", "\x05\xD5", "\x02\x01", "\x06\x07", "\x07\x08", "\x30\x01", "\x01\x33", "\x00\x10", "\x17\x16", "\x37\x3E", "\x36\x37"];
return $this->_m_lookupTable;
}
protected $_m_value;
/**
* The two bytes that the tag byte expands to,
* based on the fixed lookup table.
*/
public function value() {
if ($this->_m_value !== null)
return $this->_m_value;
$this->_m_value = $this->lookupTable()[($this->tag() - 213)];
return $this->_m_value;
}
protected $_m_tag;
/**
* The tag byte preceding this chunk body.
*/
public function tag() { return $this->_m_tag; }
}
}
/**
* The body of an end chunk.
* This body is always empty.
*
* The last chunk in the compressed data must always be an end chunk.
* An end chunk cannot appear elsewhere in the compressed data.
*/
namespace Dcmp1\Chunk {
class EndBody extends \Kaitai\Struct\Struct {
public function __construct(\Kaitai\Struct\Stream $_io, \Dcmp1\Chunk $_parent = null, \Dcmp1 $_root = null) {
parent::__construct($_io, $_parent, $_root);
$this->_read();
}
private function _read() {
}
}
}
/**
* The body of an extended chunk.
* The meaning of this chunk depends on the extended tag byte stored in the chunk data.
*/
namespace Dcmp1\Chunk {
class ExtendedBody extends \Kaitai\Struct\Struct {
public function __construct(\Kaitai\Struct\Stream $_io, \Dcmp1\Chunk $_parent = null, \Dcmp1 $_root = null) {
parent::__construct($_io, $_parent, $_root);
$this->_read();
}
private function _read() {
$this->_m_tag = $this->_io->readU1();
switch ($this->tag()) {
case 2:
$this->_m_body = new \Dcmp1\Chunk\ExtendedBody\RepeatBody($this->_io, $this, $this->_root);
break;
}
}
protected $_m_tag;
protected $_m_body;
/**
* The chunk's extended tag byte.
* This controls the structure of the body and the meaning of the chunk.
*/
public function tag() { return $this->_m_tag; }
/**
* The chunk's body.
*/
public function body() { return $this->_m_body; }
}
}
/**
* The body of a repeat chunk.
*
* This chunk expands to the same byte repeated a number of times,
* i. e. it implements a form of run-length encoding.
*/
namespace Dcmp1\Chunk\ExtendedBody {
class RepeatBody extends \Kaitai\Struct\Struct {
public function __construct(\Kaitai\Struct\Stream $_io, \Dcmp1\Chunk\ExtendedBody $_parent = null, \Dcmp1 $_root = null) {
parent::__construct($_io, $_parent, $_root);
$this->_read();
}
private function _read() {
$this->_m_toRepeatRaw = new \DcmpVariableLengthInteger($this->_io);
$this->_m_repeatCountM1Raw = new \DcmpVariableLengthInteger($this->_io);
}
protected $_m_toRepeat;
/**
* The value to repeat.
*
* Although it is stored as a variable-length integer,
* this value must fit into an unsigned 8-bit integer.
*/
public function toRepeat() {
if ($this->_m_toRepeat !== null)
return $this->_m_toRepeat;
$this->_m_toRepeat = $this->toRepeatRaw()->value();
return $this->_m_toRepeat;
}
protected $_m_repeatCountM1;
/**
* The number of times to repeat the value,
* minus one.
*
* This value must not be negative.
*/
public function repeatCountM1() {
if ($this->_m_repeatCountM1 !== null)
return $this->_m_repeatCountM1;
$this->_m_repeatCountM1 = $this->repeatCountM1Raw()->value();
return $this->_m_repeatCountM1;
}
protected $_m_repeatCount;
/**
* The number of times to repeat the value.
*
* This value must be positive.
*/
public function repeatCount() {
if ($this->_m_repeatCount !== null)
return $this->_m_repeatCount;
$this->_m_repeatCount = ($this->repeatCountM1() + 1);
return $this->_m_repeatCount;
}
protected $_m_toRepeatRaw;
protected $_m_repeatCountM1Raw;
/**
* Raw variable-length integer representation of `to_repeat`.
*/
public function toRepeatRaw() { return $this->_m_toRepeatRaw; }
/**
* Raw variable-length integer representation of `repeat_count_m1`.
*/
public function repeatCountM1Raw() { return $this->_m_repeatCountM1Raw; }
}
}
namespace Dcmp1\Chunk {
class TagKind {
const INVALID = -1;
const LITERAL = 0;
const BACKREFERENCE = 1;
const TABLE_LOOKUP = 2;
const EXTENDED = 3;
const END = 4;
}
}