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