cannam@128: 
cannam@128: Overview
cannam@128: ========
cannam@128: 
cannam@128: This directory contains an update to the ZLib interface unit,
cannam@128: distributed by Borland as a Delphi supplemental component.
cannam@128: 
cannam@128: The original ZLib unit is Copyright (c) 1997,99 Borland Corp.,
cannam@128: and is based on zlib version 1.0.4.  There are a series of bugs
cannam@128: and security problems associated with that old zlib version, and
cannam@128: we recommend the users to update their ZLib unit.
cannam@128: 
cannam@128: 
cannam@128: Summary of modifications
cannam@128: ========================
cannam@128: 
cannam@128: - Improved makefile, adapted to zlib version 1.2.1.
cannam@128: 
cannam@128: - Some field types from TZStreamRec are changed from Integer to
cannam@128:   Longint, for consistency with the zlib.h header, and for 64-bit
cannam@128:   readiness.
cannam@128: 
cannam@128: - The zlib_version constant is updated.
cannam@128: 
cannam@128: - The new Z_RLE strategy has its corresponding symbolic constant.
cannam@128: 
cannam@128: - The allocation and deallocation functions and function types
cannam@128:   (TAlloc, TFree, zlibAllocMem and zlibFreeMem) are now cdecl,
cannam@128:   and _malloc and _free are added as C RTL stubs.  As a result,
cannam@128:   the original C sources of zlib can be compiled out of the box,
cannam@128:   and linked to the ZLib unit.
cannam@128: 
cannam@128: 
cannam@128: Suggestions for improvements
cannam@128: ============================
cannam@128: 
cannam@128: Currently, the ZLib unit provides only a limited wrapper around
cannam@128: the zlib library, and much of the original zlib functionality is
cannam@128: missing.  Handling compressed file formats like ZIP/GZIP or PNG
cannam@128: cannot be implemented without having this functionality.
cannam@128: Applications that handle these formats are either using their own,
cannam@128: duplicated code, or not using the ZLib unit at all.
cannam@128: 
cannam@128: Here are a few suggestions:
cannam@128: 
cannam@128: - Checksum class wrappers around adler32() and crc32(), similar
cannam@128:   to the Java classes that implement the java.util.zip.Checksum
cannam@128:   interface.
cannam@128: 
cannam@128: - The ability to read and write raw deflate streams, without the
cannam@128:   zlib stream header and trailer.  Raw deflate streams are used
cannam@128:   in the ZIP file format.
cannam@128: 
cannam@128: - The ability to read and write gzip streams, used in the GZIP
cannam@128:   file format, and normally produced by the gzip program.
cannam@128: 
cannam@128: - The ability to select a different compression strategy, useful
cannam@128:   to PNG and MNG image compression, and to multimedia compression
cannam@128:   in general.  Besides the compression level
cannam@128: 
cannam@128:     TCompressionLevel = (clNone, clFastest, clDefault, clMax);
cannam@128: 
cannam@128:   which, in fact, could have used the 'z' prefix and avoided
cannam@128:   TColor-like symbols
cannam@128: 
cannam@128:     TCompressionLevel = (zcNone, zcFastest, zcDefault, zcMax);
cannam@128: 
cannam@128:   there could be a compression strategy
cannam@128: 
cannam@128:     TCompressionStrategy = (zsDefault, zsFiltered, zsHuffmanOnly, zsRle);
cannam@128: 
cannam@128: - ZIP and GZIP stream handling via TStreams.
cannam@128: 
cannam@128: 
cannam@128: --
cannam@128: Cosmin Truta <cosmint@cs.ubbcluj.ro>