76 lines
2.4 KiB
Text
76 lines
2.4 KiB
Text
|
|
Overview
|
|
========
|
|
|
|
This directory contains an update to the ZLib interface unit,
|
|
distributed by Borland as a Delphi supplemental component.
|
|
|
|
The original ZLib unit is Copyright (c) 1997,99 Borland Corp.,
|
|
and is based on zlib version 1.0.4. There are a series of bugs
|
|
and security problems associated with that old zlib version, and
|
|
we recommend the users to update their ZLib unit.
|
|
|
|
|
|
Summary of modifications
|
|
========================
|
|
|
|
- Improved makefile, adapted to zlib version 1.2.1.
|
|
|
|
- Some field types from TZStreamRec are changed from Integer to
|
|
Longint, for consistency with the zlib.h header, and for 64-bit
|
|
readiness.
|
|
|
|
- The zlib_version constant is updated.
|
|
|
|
- The new Z_RLE strategy has its corresponding symbolic constant.
|
|
|
|
- The allocation and deallocation functions and function types
|
|
(TAlloc, TFree, zlibAllocMem and zlibFreeMem) are now cdecl,
|
|
and _malloc and _free are added as C RTL stubs. As a result,
|
|
the original C sources of zlib can be compiled out of the box,
|
|
and linked to the ZLib unit.
|
|
|
|
|
|
Suggestions for improvements
|
|
============================
|
|
|
|
Currently, the ZLib unit provides only a limited wrapper around
|
|
the zlib library, and much of the original zlib functionality is
|
|
missing. Handling compressed file formats like ZIP/GZIP or PNG
|
|
cannot be implemented without having this functionality.
|
|
Applications that handle these formats are either using their own,
|
|
duplicated code, or not using the ZLib unit at all.
|
|
|
|
Here are a few suggestions:
|
|
|
|
- Checksum class wrappers around adler32() and crc32(), similar
|
|
to the Java classes that implement the java.util.zip.Checksum
|
|
interface.
|
|
|
|
- The ability to read and write raw deflate streams, without the
|
|
zlib stream header and trailer. Raw deflate streams are used
|
|
in the ZIP file format.
|
|
|
|
- The ability to read and write gzip streams, used in the GZIP
|
|
file format, and normally produced by the gzip program.
|
|
|
|
- The ability to select a different compression strategy, useful
|
|
to PNG and MNG image compression, and to multimedia compression
|
|
in general. Besides the compression level
|
|
|
|
TCompressionLevel = (clNone, clFastest, clDefault, clMax);
|
|
|
|
which, in fact, could have used the 'z' prefix and avoided
|
|
TColor-like symbols
|
|
|
|
TCompressionLevel = (zcNone, zcFastest, zcDefault, zcMax);
|
|
|
|
there could be a compression strategy
|
|
|
|
TCompressionStrategy = (zsDefault, zsFiltered, zsHuffmanOnly, zsRle);
|
|
|
|
- ZIP and GZIP stream handling via TStreams.
|
|
|
|
|
|
--
|
|
Cosmin Truta <cosmint@cs.ubbcluj.ro>
|