1
2Overview
3========
4
5This directory contains an update to the ZLib interface unit,
6distributed by Borland as a Delphi supplemental component.
7
8The original ZLib unit is Copyright (c) 1997,99 Borland Corp.,
9and is based on zlib version 1.0.4.  There are a series of bugs
10and security problems associated with that old zlib version, and
11we recommend the users to update their ZLib unit.
12
13
14Summary 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
34Suggestions for improvements
35============================
36
37Currently, the ZLib unit provides only a limited wrapper around
38the zlib library, and much of the original zlib functionality is
39missing.  Handling compressed file formats like ZIP/GZIP or PNG
40cannot be implemented without having this functionality.
41Applications that handle these formats are either using their own,
42duplicated code, or not using the ZLib unit at all.
43
44Here 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--
76Cosmin Truta <cosmint@cs.ubbcluj.ro>
77