
		ChangeLog file for zlib

Changes in 1.1.3 (9 July 1998)
- fix "an inflate input buffer bug that shows up on rare but persistent
  occasions" (Mark)
- fix gzread and gztell for concatenated .gz files (Didier Le Botlan)
- fix gzseek(..., SEEK_SET) in write mode
- fix crc check after a gzeek (Frank Faubert)
- fix miniunzip when the last entry in a zip file is itself a zip file
  (J Lillge)
- add contrib/asm586 and contrib/asm686 (Brian Raiter)
  See http://www.muppetlabs.com/~breadbox/software/assembly.html
- add support for Delphi 3 in contrib/delphi (Bob Dellaca)
- add support for C++Builder 3 and Delphi 3 in contrib/delphi2 (Davide Moretti)
- do not exit prematurely in untgz if 0 at start of block (Magnus Holmgren)
- use macro EXTERN instead of extern to support DLL for BeOS (Sander Stoks)
- added a FAQ file

- Support gzdopen on Mac with Metrowerks (Jason Linhart)
- Do not redefine Byte on Mac (Brad Pettit & Jason Linhart)
- define SEEK_END too if SEEK_SET is not defined (Albert Chin-A-Young)
- avoid some warnings with Borland C (Tom Tanner)
- fix a problem in contrib/minizip/zip.c for 16-bit MSDOS (Gilles Vollant)
- emulate utime() for WIN32 in contrib/untgz  (Gilles Vollant)
- allow several arguments to configure (Tim Mooney, Frodo Looijaard)
- use libdir and includedir in Makefile.in (Tim Mooney)
- support shared libraries on OSF1 V4 (Tim Mooney)
- remove so_locations in "make clean"  (Tim Mooney)
- fix maketree.c compilation error (Glenn, Mark)
- Python interface to zlib now in Python 1.5 (Jeremy Hylton)
- new Makefile.riscos (Rich Walker)
- initialize static descriptors in trees.c for embedded targets (Nick Smith)
- use "foo-gz" in example.c for RISCOS and VMS (Nick Smith)
- add the OS/2 files in Makefile.in too (Andrew Zabolotny)
- fix fdopen and halloc macros for Microsoft C 6.0 (Tom Lane)
- fix maketree.c to allow clean compilation of inffixed.h (Mark)
- fix parameter check in deflateCopy (Gunther Nikl)
- cleanup trees.c, use compressed_len only in debug mode (Christian Spieler)
- Many portability patches by Christian Spieler:
  . zutil.c, zutil.h: added "const" for zmem*
  . Make_vms.com: fixed some typos
  . Make_vms.com: msdos/Makefile.*: removed zutil.h from some dependency lists
  . msdos/Makefile.msc: remove "default rtl link library" info from obj files
  . msdos/Makefile.*: use model-dependent name for the built zlib library
  . msdos/Makefile.emx, nt/Makefile.emx, nt/Makefile.gcc:
     new makefiles, for emx (DOS/OS2), emx&rsxnt and mingw32 (Windows 9x / NT)
- use define instead of typedef for Bytef also for MSC small/medium (Tom Lane)
- replace __far with _far for better portability (Christian Spieler, Tom Lane)
- fix test for errno.h in configure (Tim Newsham)

Changes in 1.1.2 (19 March 98)
- added contrib/minzip, mini zip and unzip based on zlib (Gilles Vollant)
  See http://www.winimage.com/zLibDll/unzip.html
- preinitialize the inflate tables for fixed codes, to make the code
  completely thread safe (Mark)
- some simplifications and slight speed-up to the inflate code (Mark)
- fix gzeof on non-compressed files (Allan Schrum)
- add -std1 option in configure for OSF1 to fix gzprintf (Martin Mokrejs)
- use default value of 4K for Z_BUFSIZE for 16-bit MSDOS (Tim Wegner + Glenn)
- added os2/Makefile.def and os2/zlib.def (Andrew Zabolotny)
- add shared lib support for UNIX_SV4.2MP (MATSUURA Takanori)
- do not wrap extern "C" around system includes (Tom Lane)
- mention zlib binding for TCL in README (Andreas Kupries)
- added amiga/Makefile.pup for Amiga powerUP SAS/C PPC (Andreas Kleinert)
- allow "make install prefix=..." even after configure (Glenn Randers-Pehrson)
- allow "configure --prefix $HOME" (Tim Mooney)
- remove warnings in example.c and gzio.c (Glenn Randers-Pehrson)
- move Makefile.sas to amiga/Makefile.sas

Changes in 1.1.1 (27 Feb 98)
- fix macros _tr_tally_* in deflate.h for debug mode  (Glenn Randers-Pehrson)
- remove block truncation heuristic which had very marginal effect for zlib
  (smaller lit_bufsize than in gzip 1.2.4) and degraded a little the
  compression ratio on some files. This also allows inlining _tr_tally for
  matches in deflate_slow.
- added msdos/Makefile.w32 for WIN32 Microsoft Visual C++ (Bob Frazier)

Changes in 1.1.0 (24 Feb 98)
- do not return STREAM_END prematurely in inflate (John Bowler)
- revert to the zlib 1.0.8 inflate to avoid the gcc 2.8.0 bug (Jeremy Buhler)
- compile with -DFASTEST to get compression code optimized for speed only
- in minigzip, try mmap'ing the input file first (Miguel Albrecht)
- increase size of I/O buffers in minigzip.c and gzio.c (not a big gain
  on Sun but significant on HP)

- add a pointer to experimental unzip library in README (Gilles Vollant)
- initialize variable gcc in configure (Chris Herborth)

Changes in 1.0.9 (17 Feb 1998)
- added gzputs and gzgets functions
- do not clear eof flag in gzseek (Mark Diekhans)
- fix gzseek for files in transparent mode (Mark Diekhans)
- do not assume that vsprintf returns the number of bytes written (Jens Krinke)
- replace EXPORT with ZEXPORT to avoid conflict with other programs
- added compress2 in zconf.h, zlib.def, zlib.dnt
- new asm code from Gilles Vollant in contrib/asm386
- simplify the inflate code (Mark):
 . Replace ZALLOC's in huft_build() with single ZALLOC in inflate_blocks_new()
 . ZALLOC the length list in inflate_trees_fixed() instead of using stack
 . ZALLOC the value area for huft_build() instead of using stack
 . Simplify Z_FINISH check in inflate()

- Avoid gcc 2.8.0 comparison bug a little differently than zlib 1.0.8
- in inftrees.c, avoid cc -O bug on HP (Farshid Elahi)
- in zconf.h move the ZLIB_DLL stuff earlier to avoid problems with
  the declaration of FAR (Gilles VOllant)
- install libz.so* with mode 755 (executable) instead of 644 (Marc Lehmann)
- read_buf buf parameter of type Bytef* instead of charf*
- zmemcpy parameters are of type Bytef*, not charf* (Joseph Strout)
- do not redeclare unlink in minigzip.c for WIN32 (John Bowler)
- fix check for presence of directories in "make install" (Ian Willis)

Changes in 1.0.8 (27 Jan 1998)
- fixed offsets in contrib/asm386/gvmat32.asm (Gilles Vollant)
- fix gzgetc and gzputc for big endian systems (Markus Oberhumer)
- added compress2() to allow setting the compression level
- include sys/types.h to get off_t on some systems (Marc Lehmann & QingLong)
- use constant arrays for the static trees in trees.c instead of computing
  them at run time (thanks to Ken Raeburn for this suggestion). To create
  trees.h, compile with GEN_TREES_H and run "make test".
- check return code of example in "make test" and display result
- pass minigzip command line options to file_compress
- simplifying code of inflateSync to avoid gcc 2.8 bug

- support CC="gcc -Wall" in configure -s (QingLong)
- avoid a flush caused by ftell in gzopen for write mode (Ken Raeburn)
- fix test for shared library support to avoid compiler warnings
- zlib.lib -> zlib.dll in msdos/zlib.rc (Gilles Vollant)
- check for TARGET_OS_MAC in addition to MACOS (Brad Pettit)
- do not use fdopen for Metrowerks on Mac (Brad Pettit))
- add checks for gzputc and gzputc in example.c
- avoid warnings in gzio.c and deflate.c (Andreas Kleinert)
- use const for the CRC table (Ken Raeburn)
- fixed "make uninstall" for shared libraries
- use Tracev instead of Trace in infblock.c
- in example.c use correct compressed length for test_sync
- suppress +vnocompatwarnings in configure for HPUX (not always supported)

Changes in 1.0.7 (20 Jan 1998)
- fix gzseek which was broken in write mode
- return error for gzseek to negative absolute position
- fix configure for Linux (Chun-Chung Chen)
- increase stack space for MSC (Tim Wegner)
- get_crc_table and inflateSyncPoint are EXPORTed (Gilles Vollant)
- define EXPORTVA for gzprintf (Gilles Vollant)
- added man page zlib.3 (Rick Rodgers)
- for contrib/untgz, fix makedir() and improve Makefile

- check gzseek in write mode in example.c
- allocate extra buffer for seeks only if gzseek is actually called
- avoid signed/unsigned comparisons (Tim Wegner, Gilles Vollant)
- add inflateSyncPoint in zconf.h
- fix list of exported functions in nt/zlib.dnt and mdsos/zlib.def

Changes in 1.0.6 (19 Jan 1998)
- add functions gzprintf, gzputc, gzgetc, gztell, gzeof, gzseek, gzrewind and
  gzsetparams (thanks to Roland Giersig and Kevin Ruland for some of this code)
- Fix a deflate bug occuring only with compression level 0 (thanks to
  Andy Buckler for finding this one).
- In minigzip, pass transparently also the first byte for .Z files.
- return Z_BUF_ERROR instead of Z_OK if output buffer full in uncompress()
- check Z_FINISH in inflate (thanks to Marc Schluper)
- Implement deflateCopy (thanks to Adam Costello)
- make static libraries by default in configure, add --shared option.
- move MSDOS or Windows specific files to directory msdos
- suppress the notion of partial flush to simplify the interface
  (but the symbol Z_PARTIAL_FLUSH is kept for compatibility with 1.0.4)
- suppress history buffer provided by application to simplify the interface
  (this feature was not implemented anyway in 1.0.4)
- next_in and avail_in must be initialized before calling inflateInit or
  inflateInit2
- add EXPORT in all exported functions (for Windows DLL)
- added Makefile.nt (thanks to Stephen Williams)
- added the unsupported "contrib" directory:
   contrib/asm386/ by Gilles Vollant <info@winimage.com>
	386 asm code replacing longest_match().
   contrib/iostream/ by Kevin Ruland <kevin@rodin.wustl.edu>
        A C++ I/O streams interface to the zlib gz* functions
   contrib/iostream2/  by Tyge Løvset <Tyge.Lovset@cmr.no>
	Another C++ I/O streams interface
   contrib/untgz/  by "Pedro A. Aranda Guti\irrez" <paag@tid.es>
	A very simple tar.gz file extractor using zlib
   contrib/visual-basic.txt by Carlos Rios <c_rios@sonda.cl>
        How to use compress(), uncompress() and the gz* functions from VB.
- pass params -f (filtered data), -h (huffman only), -1 to -9 (compression
  level) in minigzip (thanks to Tom Lane)

- use const for rommable constants in deflate
- added test for gzseek and gztell in example.c
- add undocumented function inflateSyncPoint() (hack for Paul Mackerras)
- add undocumented function zError to convert error code to string
  (for Tim Smithers)
- Allow compilation of gzio with -DNO_DEFLATE to avoid the compression code.
- Use default memcpy for Symantec MSDOS compiler.
- Add EXPORT keyword for check_func (needed for Windows DLL)
- add current directory to LD_LIBRARY_PATH for "make test"
- create also a link for libz.so.1
- added support for FUJITSU UXP/DS (thanks to Toshiaki Nomura)
- use $(SHAREDLIB) instead of libz.so in Makefile.in (for HPUX)
- added -soname for Linux in configure (Chun-Chung Chen,
- assign numbers to the exported functions in zlib.def (for Windows DLL)
- add advice in zlib.h for best usage of deflateSetDictionary
- work around compiler bug on Atari (cast Z_NULL in call of s->checkfn)
- allow compilation with ANSI keywords only enabled for TurboC in large model
- avoid "versionString"[0] (Borland bug)
- add NEED_DUMMY_RETURN for Borland
- use variable z_verbose for tracing in debug mode (L. Peter Deutsch).
- allow compilation with CC
- defined STDC for OS/2 (David Charlap)	
- limit external names to 8 chars for MVS (Thomas Lund)
- in minigzip.c, use static buffers only for 16-bit systems
- fix suffix check for "minigzip -d foo.gz"
- do not return an error for the 2nd of two consecutive gzflush() (Felix Lee)
- use _fdopen instead of fdopen for MSC >= 6.0 (Thomas Fanslau)
- added makelcc.bat for lcc-win32 (Tom St Denis)
- in Makefile.dj2, use copy and del instead of install and rm (Frank Donahoe)
- Avoid expanded $Id: ChangeLog,v 1.1.1.1 2001/07/18 11:06:07 root Exp $. Use "rcs -kb" or "cvs admin -kb" to avoid Id expansion.
- check for unistd.h in configure (for off_t)
- remove useless check parameter in inflate_blocks_free
- avoid useless assignment of s->check to itself in inflate_blocks_new
- do not flush twice in gzclose (thanks to Ken Raeburn)
- rename FOPEN as F_OPEN to avoid clash with /usr/include/sys/file.h
- use NO_ERRNO_H instead of enumeration of operating systems with errno.h
- work around buggy fclose on pipes for HP/UX
- support zlib DLL with BORLAND C++ 5.0 (thanks to Glenn Randers-Pehrson)
- fix configure if CC is already equal to gcc

Changes in 1.0.5 (3 Jan 98)
- Fix inflate to terminate gracefully when fed corrupted or invalid data
- Use const for rommable constants in inflate
- Eliminate memory leaks on error conditions in inflate
- Removed some vestigial code in inflate
- Update web address in README
  
Changes in 1.0.4 (24 Jul 96)
- In very rare conditions, deflate(s, Z_FINISH) could fail to produce an EOF
  bit, so the decompressor could decompress all the correct data but went
  on to attempt decompressing extra garbage data. This affected minigzip too.
- zlibVersion and gzerror return const char* (needed for DLL)
- port to RISCOS (no fdopen, no multiple dots, no unlink, no fileno)
- use z_error only for DEBUG (avoid problem with DLLs)

Changes in 1.0.3 (2 Jul 96)
- use z_streamp instead of z_stream *, which is now a far pointer in MSDOS
  small and medium models; this makes the library incompatible with previous
  versions for these models. (No effect in large model or on other systems.)
- return OK instead of BUF_ERROR if previous deflate call returned with
  avail_out as zero but there is nothing to do
- added memcmp for non STDC compilers
- define NO_DUMMY_DECL for more Mac compilers (.h files merged incorrectly)
- define __32BIT__ if __386__ or i386 is defined (pb. with Watcom and SCO)
- better check for 16-bit mode MSC (avoids problem with Symantec)

Changes in 1.0.2 (23 May 96)
- added Windows DLL support
- added a function zlibVersion (for the DLL support)
- fixed declarations using Bytef in infutil.c (pb with MSDOS medium model)
- Bytef is define's instead of typedef'd only for Borland C
- avoid reading uninitialized memory in example.c
- mention in README that the zlib format is now RFC1950
- updated Makefile.dj2
- added algorithm.doc

Changes in 1.0.1 (20 May 96) [1.0 skipped to avoid confusion]
- fix array overlay in deflate.c which sometimes caused bad compressed data
- fix inflate bug with empty stored block
- fix MSDOS medium model which was broken in 0.99
- fix deflateParams() which could generated bad compressed data.
- Bytef is define'd instead of typedef'ed (work around Borland bug)
- added an INDEX file
- new makefiles for DJGPP (Makefile.dj2), 32-bit Borland (Makefile.b32),
  Watcom (Makefile.wat), Amiga SAS/C (Makefile.sas)
- speed up adler32 for modern machines without auto-increment
- added -ansi for IRIX in configure
- static_init_done in trees.c is an int
- define unlink as delete for VMS
- fix configure for QNX
- add configure branch for SCO and HPUX
- avoid many warnings (unused variables, dead assignments, etc...)
- no fdopen for BeOS
- fix the Watcom fix for 32 bit mode (define FAR as empty)
- removed redefinition of Byte for MKWERKS
- work around an MWKERKS bug (incorrect merge of all .h files)

Changes in 0.99 (27 Jan 96)
- allow preset dictionary shared between compressor and decompressor
- allow compression level 0 (no compression)
- add deflateParams in zlib.h: allow dynamic change of compression level
  and compression strategy.
- test large buffers and deflateParams in example.c
- add optional "configure" to build zlib as a shared library
- suppress Makefile.qnx, use configure instead
- fixed deflate for 64-bit systems (detected on Cray)
- fixed inflate_blocks for 64-bit systems (detected on Alpha)
- declare Z_DEFLATED in zlib.h (possible parameter for deflateInit2)
- always return Z_BUF_ERROR when deflate() has nothing to do
- deflateInit and inflateInit are now macros to allow version checking
- prefix all global functions and types with z_ with -DZ_PREFIX
- make falloc completely reentrant (inftrees.c)
- fixed very unlikely race condition in ct_static_init
- free in reverse order of allocation to help memory manager
- use zlib-1.0/* instead of zlib/* inside the tar.gz
- make zlib warning-free with "gcc -O3 -Wall -Wwrite-strings -Wpointer-arith
  -Wconversion -Wstrict-prototypes -Wmissing-prototypes"
- allow gzread on concatenated .gz files
- deflateEnd now returns Z_DATA_ERROR if it was premature
- deflate is finally (?) fully deterministic (no matches beyond end of input)
- Document Z_SYNC_FLUSH
- add uninstall in Makefile
- Check for __cpluplus in zlib.h
- Better test in ct_align for partial flush
- avoid harmless warnings for Borland C++
- initialize hash_head in deflate.c
- avoid warning on fdopen (gzio.c) for HP cc -Aa
- include stdlib.h for STDC compilers
- include errno.h for Cray
- ignore error if ranlib doesn't exist
- call ranlib twice for NeXTSTEP
- use exec_prefix instead of prefix for libz.a
- renamed ct_* as _tr_* to avoid conflict with applications
- clear z->msg in inflateInit2 before any error return
- initialize opaque in example.c, gzio.c, deflate.c and inflate.c
- fixed typo in zconf.h (_GNUC__ => __GNUC__)
- check for WIN32 in zconf.h and zutil.c (avoid farmalloc in 32-bit mode)
- fix typo in Make_vms.com (f$trnlnm -> f$getsyi)
- in fcalloc, normalize pointer if size > 65520 bytes
- don't use special fcalloc for 32 bit Borland C++
- use STDC instead of __GO32__ to avoid redeclaring exit, calloc, etc...
- use Z_BINARY instead of BINARY
- document that gzclose after gzdopen will close the file
- allow "a" as mode in gzopen.
- fix error checking in gzread
- allow skipping .gz extra-field on pipes
- added reference to Perl interface in README
- put the crc table in FAR data (I dislike more and more the medium model :)
- added get_crc_table
- added a dimension to all arrays (Borland C can't count).
- workaround Borland C bug in declaration of inflate_codes_new & inflate_fast
- guard against multiple inclusion of *.h (for precompiled header on Mac)
- Watcom C pretends to be Microsoft C small model even in 32 bit mode.
- don't use unsized arrays to avoid silly warnings by Visual C++:
     warning C4746: 'inflate_mask' : unsized array treated as  '__far'
     (what's wrong with far data in far model?).
- define enum out of inflate_blocks_state to allow compilation with C++

Changes in 0.95 (16 Aug 95)
- fix MSDOS small and medium model (now easier to adapt to any compiler)
- inlined send_bits
- fix the final (:-) bug for deflate with flush (output was correct but
  not completely flushed in rare occasions).
- default window size is same for compression and decompression
  (it's now sufficient to set MAX_WBITS in zconf.h).
- voidp -> voidpf and voidnp -> voidp (for consistency with other
  typedefs and because voidnp was not near in large model).

Changes in 0.94 (13 Aug 95)
- support MSDOS medium model
- fix deflate with flush (could sometimes generate bad output)
- fix deflateReset (zlib header was incorrectly suppressed)
- added support for VMS
- allow a compression level in gzopen()
- gzflush now calls fflush
- For deflate with flush, flush even if no more input is provided.
- rename libgz.a as libz.a
- avoid complex expression in infcodes.c triggering Turbo C bug
- work around a problem with gcc on Alpha (in INSERT_STRING)
- don't use inline functions (problem with some gcc versions)
- allow renaming of Byte, uInt, etc... with #define.
- avoid warning about (unused) pointer before start of array in deflate.c
- avoid various warnings in gzio.c, example.c, infblock.c, adler32.c, zutil.c
- avoid reserved word 'new' in trees.c

Changes in 0.93 (25 June 95)
- temporarily disable inline functions
- make deflate deterministic
- give enough lookahead for PARTIAL_FLUSH
- Set binary mode for stdin/stdout in minigzip.c for OS/2
- don't even use signed char in inflate (not portable enough)
- fix inflate memory leak for segmented architectures

Changes in 0.92 (3 May 95)
- don't assume that char is signed (problem on SGI)
- Clear bit buffer when starting a stored block
- no memcpy on Pyramid
- suppressed inftest.c
- optimized fill_window, put longest_match inline for gcc
- optimized inflate on stored blocks.
- untabify all sources to simplify patches

Changes in 0.91 (2 May 95)
- Default MEM_LEVEL is 8 (not 9 for Unix) as documented in zlib.h
- Document the memory requirements in zconf.h
- added "make install"
- fix sync search logic in inflateSync
- deflate(Z_FULL_FLUSH) now works even if output buffer too short
- after inflateSync, don't scare people with just "lo world"
- added support for DJGPP

Changes in 0.9 (1 May 95)
- don't assume that zalloc clears the allocated memory (the TurboC bug
  was Mark's bug after all :)
- let again gzread copy uncompressed data unchanged (was working in 0.71)
- deflate(Z_FULL_FLUSH), inflateReset and inflateSync are now fully implemented
- added a test of inflateSync in example.c
- moved MAX_WBITS to zconf.h because users might want to change that.
- document explicitly that zalloc(64K) on MSDOS must return a normalized
  pointer (zero offset)
- added Makefiles for Microsoft C, Turbo C, Borland C++
- faster crc32()

Changes in 0.8 (29 April 95)
- added fast inflate (inffast.c)
- deflate(Z_FINISH) now returns Z_STREAM_END when done. Warning: this
  is incompatible with previous versions of zlib which returned Z_OK.
- work around a TurboC compiler bug (bad code for b << 0, see infutil.h)
  (actually that was not a compiler bug, see 0.81 above)
- gzread no longer reads one extra byte in certain cases
- In gzio destroy(), don't reference a freed structure
- avoid many warnings for MSDOS
- avoid the ERROR symbol which is used by MS Windows

Changes in 0.71 (14 April 95)
- Fixed more MSDOS compilation problems :( There is still a bug with
  TurboC large model.

Changes in 0.7 (14 April 95)
- Added full inflate support.
- Simplified the crc32() interface. The pre- and post-conditioning
  (one's complement) is now done inside crc32(). WARNING: this is
  incompatible with previous versions; see zlib.h for the new usage.

Changes in 0.61 (12 April 95)
- workaround for a bug in TurboC. example and minigzip now work on MSDOS.

Changes in 0.6 (11 April 95)
- added minigzip.c
- added gzdopen to reopen a file descriptor as gzFile
- added transparent reading of non-gziped files in gzread.
- fixed bug in gzread (don't read crc as data)
- fixed bug in destroy (gzio.c) (don't return Z_STREAM_END for gzclose).
- don't allocate big arrays in the stack (for MSDOS)
- fix some MSDOS compilation problems

Changes in 0.5:
- do real compression in deflate.c. Z_PARTIAL_FLUSH is supported but
  not yet Z_FULL_FLUSH.
- support decompression but only in a single step (forced Z_FINISH)
- added opaque object for zalloc and zfree.
- added deflateReset and inflateReset
- added a variable zlib_version for consistency checking.
- renamed the 'filter' parameter of deflateInit2 as 'strategy'.
  Added Z_FILTERED and Z_HUFFMAN_ONLY constants.

Changes in 0.4:
- avoid "zip" everywhere, use zlib instead of ziplib.
- suppress Z_BLOCK_FLUSH, interpret Z_PARTIAL_FLUSH as block flush
  if compression method == 8.
- added adler32 and crc32
- renamed deflateOptions as deflateInit2, call one or the other but not both
- added the method parameter for deflateInit2.
- added inflateInit2
- simplied considerably deflateInit and inflateInit by not supporting
  user-provided history buffer. This is supported only in deflateInit2
  and inflateInit2.

Changes in 0.3:
- prefix all macro names with Z_
- use Z_FINISH instead of deflateEnd to finish compression.
- added Z_HUFFMAN_ONLY
- added gzerror()
