9e052883 |
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> |