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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> |
