| 1 |
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| 2 | Overview
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| 3 | ========
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| 4 |
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| 5 | This directory contains an update to the ZLib interface unit,
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| 6 | distributed by Borland as a Delphi supplemental component.
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| 7 |
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| 8 | The original ZLib unit is Copyright (c) 1997,99 Borland Corp.,
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| 9 | and is based on zlib version 1.0.4. There are a series of bugs
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| 10 | and security problems associated with that old zlib version, and
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| 11 | we recommend the users to update their ZLib unit.
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| 12 |
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| 13 |
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| 14 | Summary of modifications
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| 15 | ========================
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| 16 |
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| 17 | - Improved makefile, adapted to zlib version 1.2.1.
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| 18 |
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| 19 | - Some field types from TZStreamRec are changed from Integer to
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| 20 | Longint, for consistency with the zlib.h header, and for 64-bit
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| 21 | readiness.
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| 22 |
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| 23 | - The zlib_version constant is updated.
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| 24 |
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| 25 | - The new Z_RLE strategy has its corresponding symbolic constant.
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| 26 |
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| 27 | - The allocation and deallocation functions and function types
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| 28 | (TAlloc, TFree, zlibAllocMem and zlibFreeMem) are now cdecl,
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| 29 | and _malloc and _free are added as C RTL stubs. As a result,
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| 30 | the original C sources of zlib can be compiled out of the box,
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| 31 | and linked to the ZLib unit.
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| 32 |
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| 33 |
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| 34 | Suggestions for improvements
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| 35 | ============================
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| 36 |
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| 37 | Currently, the ZLib unit provides only a limited wrapper around
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| 38 | the zlib library, and much of the original zlib functionality is
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| 39 | missing. Handling compressed file formats like ZIP/GZIP or PNG
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| 40 | cannot be implemented without having this functionality.
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| 41 | Applications that handle these formats are either using their own,
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| 42 | duplicated code, or not using the ZLib unit at all.
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| 43 |
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| 44 | Here are a few suggestions:
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| 45 |
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| 46 | - Checksum class wrappers around adler32() and crc32(), similar
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| 47 | to the Java classes that implement the java.util.zip.Checksum
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| 48 | interface.
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| 49 |
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| 50 | - The ability to read and write raw deflate streams, without the
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| 51 | zlib stream header and trailer. Raw deflate streams are used
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| 52 | in the ZIP file format.
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| 53 |
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| 54 | - The ability to read and write gzip streams, used in the GZIP
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| 55 | file format, and normally produced by the gzip program.
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| 56 |
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| 57 | - The ability to select a different compression strategy, useful
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| 58 | to PNG and MNG image compression, and to multimedia compression
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| 59 | in general. Besides the compression level
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| 60 |
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| 61 | TCompressionLevel = (clNone, clFastest, clDefault, clMax);
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| 62 |
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| 63 | which, in fact, could have used the 'z' prefix and avoided
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| 64 | TColor-like symbols
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| 65 |
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| 66 | TCompressionLevel = (zcNone, zcFastest, zcDefault, zcMax);
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| 67 |
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| 68 | there could be a compression strategy
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| 69 |
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| 70 | TCompressionStrategy = (zsDefault, zsFiltered, zsHuffmanOnly, zsRle);
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| 71 |
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| 72 | - ZIP and GZIP stream handling via TStreams.
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| 73 |
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| 74 |
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| 75 | --
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| 76 | Cosmin Truta <[email protected]>
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