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authordkf <donal.k.fellows@manchester.ac.uk>2008-12-19 14:44:48 (GMT)
committerdkf <donal.k.fellows@manchester.ac.uk>2008-12-19 14:44:48 (GMT)
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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>