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+
+Overview
+========
+
+This directory contains an update to the PTLib interface unit,
+distributed by Borland as a Delphi supplemental component.
+
+The original PTLib unit is Copyright (c) 1997,99 Borland Corp.,
+and is based on PTlibzippy version 1.0.4.  There are a series of bugs
+and security problems associated with that old PTlibzippy version, and
+we recommend the users to update their PTLib unit.
+
+
+Summary of modifications
+========================
+
+- Improved makefile, adapted to PTlibzippy version 1.2.1.
+
+- Some field types from TZStreamRec are changed from Integer to
+  Longint, for consistency with the ptlibzippy.h header, and for 64-bit
+  readiness.
+
+- The ptlibzippy_version constant is updated.
+
+- The new Z_RLE strategy has its corresponding symbolic constant.
+
+- The allocation and deallocation functions and function types
+  (TAlloc, TFree, ptlibzippyAllocMem and ptlibzippyFreeMem) are now cdecl,
+  and _malloc and _free are added as C RTL stubs.  As a result,
+  the original C sources of PTlibzippy can be compiled out of the box,
+  and linked to the PTLib unit.
+
+
+Suggestions for improvements
+============================
+
+Currently, the PTLib unit provides only a limited wrapper around
+the PTlibzippy library, and much of the original PTlibzippy 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 PTLib 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
+  PTlibzippy 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>