| |
| Overview |
| ======== |
| |
| This directory contains an update to the ZLib interface unit, |
| distributed by Borland as a Delphi supplemental component. |
| |
| The original ZLib unit is Copyright (c) 1997,99 Borland Corp., |
| and is based on zlib version 1.0.4. There are a series of bugs |
| and security problems associated with that old zlib version, and |
| we recommend the users to update their ZLib unit. |
| |
| |
| Summary of modifications |
| ======================== |
| |
| - Improved makefile, adapted to zlib version 1.2.1. |
| |
| - Some field types from TZStreamRec are changed from Integer to |
| Longint, for consistency with the zlib.h header, and for 64-bit |
| readiness. |
| |
| - The zlib_version constant is updated. |
| |
| - The new Z_RLE strategy has its corresponding symbolic constant. |
| |
| - The allocation and deallocation functions and function types |
| (TAlloc, TFree, zlibAllocMem and zlibFreeMem) are now cdecl, |
| and _malloc and _free are added as C RTL stubs. As a result, |
| the original C sources of zlib can be compiled out of the box, |
| and linked to the ZLib unit. |
| |
| |
| Suggestions for improvements |
| ============================ |
| |
| Currently, the ZLib unit provides only a limited wrapper around |
| the zlib library, and much of the original zlib functionality is |
| missing. Handling compressed file formats like ZIP/GZIP or PNG |
| cannot be implemented without having this functionality. |
| Applications that handle these formats are either using their own, |
| duplicated code, or not using the ZLib unit at all. |
| |
| Here are a few suggestions: |
| |
| - Checksum class wrappers around adler32() and crc32(), similar |
| to the Java classes that implement the java.util.zip.Checksum |
| interface. |
| |
| - The ability to read and write raw deflate streams, without the |
| zlib stream header and trailer. Raw deflate streams are used |
| in the ZIP file format. |
| |
| - The ability to read and write gzip streams, used in the GZIP |
| file format, and normally produced by the gzip program. |
| |
| - The ability to select a different compression strategy, useful |
| to PNG and MNG image compression, and to multimedia compression |
| in general. Besides the compression level |
| |
| TCompressionLevel = (clNone, clFastest, clDefault, clMax); |
| |
| which, in fact, could have used the 'z' prefix and avoided |
| TColor-like symbols |
| |
| TCompressionLevel = (zcNone, zcFastest, zcDefault, zcMax); |
| |
| there could be a compression strategy |
| |
| TCompressionStrategy = (zsDefault, zsFiltered, zsHuffmanOnly, zsRle); |
| |
| - ZIP and GZIP stream handling via TStreams. |
| |
| |
| -- |
| Cosmin Truta <cosmint@cs.ubbcluj.ro> |