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- 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>
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