Chris@43: 
Chris@43: Overview
Chris@43: ========
Chris@43: 
Chris@43: This directory contains an update to the ZLib interface unit,
Chris@43: distributed by Borland as a Delphi supplemental component.
Chris@43: 
Chris@43: The original ZLib unit is Copyright (c) 1997,99 Borland Corp.,
Chris@43: and is based on zlib version 1.0.4.  There are a series of bugs
Chris@43: and security problems associated with that old zlib version, and
Chris@43: we recommend the users to update their ZLib unit.
Chris@43: 
Chris@43: 
Chris@43: Summary of modifications
Chris@43: ========================
Chris@43: 
Chris@43: - Improved makefile, adapted to zlib version 1.2.1.
Chris@43: 
Chris@43: - Some field types from TZStreamRec are changed from Integer to
Chris@43:   Longint, for consistency with the zlib.h header, and for 64-bit
Chris@43:   readiness.
Chris@43: 
Chris@43: - The zlib_version constant is updated.
Chris@43: 
Chris@43: - The new Z_RLE strategy has its corresponding symbolic constant.
Chris@43: 
Chris@43: - The allocation and deallocation functions and function types
Chris@43:   (TAlloc, TFree, zlibAllocMem and zlibFreeMem) are now cdecl,
Chris@43:   and _malloc and _free are added as C RTL stubs.  As a result,
Chris@43:   the original C sources of zlib can be compiled out of the box,
Chris@43:   and linked to the ZLib unit.
Chris@43: 
Chris@43: 
Chris@43: Suggestions for improvements
Chris@43: ============================
Chris@43: 
Chris@43: Currently, the ZLib unit provides only a limited wrapper around
Chris@43: the zlib library, and much of the original zlib functionality is
Chris@43: missing.  Handling compressed file formats like ZIP/GZIP or PNG
Chris@43: cannot be implemented without having this functionality.
Chris@43: Applications that handle these formats are either using their own,
Chris@43: duplicated code, or not using the ZLib unit at all.
Chris@43: 
Chris@43: Here are a few suggestions:
Chris@43: 
Chris@43: - Checksum class wrappers around adler32() and crc32(), similar
Chris@43:   to the Java classes that implement the java.util.zip.Checksum
Chris@43:   interface.
Chris@43: 
Chris@43: - The ability to read and write raw deflate streams, without the
Chris@43:   zlib stream header and trailer.  Raw deflate streams are used
Chris@43:   in the ZIP file format.
Chris@43: 
Chris@43: - The ability to read and write gzip streams, used in the GZIP
Chris@43:   file format, and normally produced by the gzip program.
Chris@43: 
Chris@43: - The ability to select a different compression strategy, useful
Chris@43:   to PNG and MNG image compression, and to multimedia compression
Chris@43:   in general.  Besides the compression level
Chris@43: 
Chris@43:     TCompressionLevel = (clNone, clFastest, clDefault, clMax);
Chris@43: 
Chris@43:   which, in fact, could have used the 'z' prefix and avoided
Chris@43:   TColor-like symbols
Chris@43: 
Chris@43:     TCompressionLevel = (zcNone, zcFastest, zcDefault, zcMax);
Chris@43: 
Chris@43:   there could be a compression strategy
Chris@43: 
Chris@43:     TCompressionStrategy = (zsDefault, zsFiltered, zsHuffmanOnly, zsRle);
Chris@43: 
Chris@43: - ZIP and GZIP stream handling via TStreams.
Chris@43: 
Chris@43: 
Chris@43: --
Chris@43: Cosmin Truta <cosmint@cs.ubbcluj.ro>