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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 <cosmint@cs.ubbcluj.ro>
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