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