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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> |