Contents of /branch/r3113_0.9.7_beta/3rdparty/zlib/FAQ

                Frequently Asked Questions about zlib


If your question is not there, please check the zlib home page
http://zlib.net/ which may have more recent information.
The lastest zlib FAQ is at http://zlib.net/zlib_faq.html


 1. Is zlib Y2K-compliant?

    Yes. zlib doesn't handle dates.

 2. Where can I get a Windows DLL version?

    The zlib sources can be compiled without change to produce a DLL.  See the
    file win32/DLL_FAQ.txt in the zlib distribution.  Pointers to the
    precompiled DLL are found in the zlib web site at http://zlib.net/ .

 3. Where can I get a Visual Basic interface to zlib?

    See
        * http://marknelson.us/1997/01/01/zlib-engine/
        * win32/DLL_FAQ.txt in the zlib distribution

 4. compress() returns Z_BUF_ERROR.

    Make sure that before the call of compress(), the length of the compressed
    buffer is equal to the available size of the compressed buffer and not
    zero.  For Visual Basic, check that this parameter is passed by reference
    ("as any"), not by value ("as long").

 5. deflate() or inflate() returns Z_BUF_ERROR.

    Before making the call, make sure that avail_in and avail_out are not zero.
    When setting the parameter flush equal to Z_FINISH, also make sure that
    avail_out is big enough to allow processing all pending input.  Note that a
    Z_BUF_ERROR is not fatal--another call to deflate() or inflate() can be
    made with more input or output space.  A Z_BUF_ERROR may in fact be
    unavoidable depending on how the functions are used, since it is not
    possible to tell whether or not there is more output pending when
    strm.avail_out returns with zero.  See http://zlib.net/zlib_how.html for a
    heavily annotated example.

 6. Where's the zlib documentation (man pages, etc.)?

    It's in zlib.h .  Examples of zlib usage are in the files example.c and
    minigzip.c, with more in examples/ .

 7. Why don't you use GNU autoconf or libtool or ...?

    Because we would like to keep zlib as a very small and simple package.
    zlib is rather portable and doesn't need much configuration.

 8. I found a bug in zlib.

    Most of the time, such problems are due to an incorrect usage of zlib.
    Please try to reproduce the problem with a small program and send the
    corresponding source to us at zlib@gzip.org .  Do not send multi-megabyte
    data files without prior agreement.

 9. Why do I get "undefined reference to gzputc"?

    If "make test" produces something like

       example.o(.text+0x154): undefined reference to `gzputc'

    check that you don't have old files libz.* in /usr/lib, /usr/local/lib or
    /usr/X11R6/lib. Remove any old versions, then do "make install".

10. I need a Delphi interface to zlib.

    See the contrib/delphi directory in the zlib distribution.

11. Can zlib handle .zip archives?

    Not by itself, no.  See the directory contrib/minizip in the zlib
    distribution.

12. Can zlib handle .Z files?

    No, sorry.  You have to spawn an uncompress or gunzip subprocess, or adapt
    the code of uncompress on your own.

13. How can I make a Unix shared library?

    make clean
    ./configure -s
    make

14. How do I install a shared zlib library on Unix?

    After the above, then:

    make install

    However, many flavors of Unix come with a shared zlib already installed.
    Before going to the trouble of compiling a shared version of zlib and
    trying to install it, you may want to check if it's already there!  If you
    can #include <zlib.h>, it's there.  The -lz option will probably link to
    it.  You can check the version at the top of zlib.h or with the
    ZLIB_VERSION symbol defined in zlib.h .

15. I have a question about OttoPDF.

    We are not the authors of OttoPDF. The real author is on the OttoPDF web
    site: Joel Hainley, jhainley@myndkryme.com.

16. Can zlib decode Flate data in an Adobe PDF file?

    Yes. See http://www.pdflib.com/ . To modify PDF forms, see
    http://sourceforge.net/projects/acroformtool/ .

17. Why am I getting this "register_frame_info not found" error on Solaris?

    After installing zlib 1.1.4 on Solaris 2.6, running applications using zlib
    generates an error such as:

        ld.so.1: rpm: fatal: relocation error: file /usr/local/lib/libz.so:
        symbol __register_frame_info: referenced symbol not found

    The symbol __register_frame_info is not part of zlib, it is generated by
    the C compiler (cc or gcc).  You must recompile applications using zlib
    which have this problem.  This problem is specific to Solaris.  See
    http://www.sunfreeware.com for Solaris versions of zlib and applications
    using zlib.

18. Why does gzip give an error on a file I make with compress/deflate?

    The compress and deflate functions produce data in the zlib format, which
    is different and incompatible with the gzip format.  The gz* functions in
    zlib on the other hand use the gzip format.  Both the zlib and gzip formats
    use the same compressed data format internally, but have different headers
    and trailers around the compressed data.

19. Ok, so why are there two different formats?

    The gzip format was designed to retain the directory information about a
    single file, such as the name and last modification date.  The zlib format
    on the other hand was designed for in-memory and communication channel
    applications, and has a much more compact header and trailer and uses a
    faster integrity check than gzip.

20. Well that's nice, but how do I make a gzip file in memory?

    You can request that deflate write the gzip format instead of the zlib
    format using deflateInit2().  You can also request that inflate decode the
    gzip format using inflateInit2().  Read zlib.h for more details.

21. Is zlib thread-safe?

    Yes.  However any library routines that zlib uses and any application-
    provided memory allocation routines must also be thread-safe.  zlib's gz*
    functions use stdio library routines, and most of zlib's functions use the
    library memory allocation routines by default.  zlib's *Init* functions
    allow for the application to provide custom memory allocation routines.

    Of course, you should only operate on any given zlib or gzip stream from a
    single thread at a time.

22. Can I use zlib in my commercial application?

    Yes.  Please read the license in zlib.h.

23. Is zlib under the GNU license?

    No.  Please read the license in zlib.h.

24. The license says that altered source versions must be "plainly marked". So
    what exactly do I need to do to meet that requirement?

    You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h.  In
    particular, the final version number needs to be changed to "f", and an
    identification string should be appended to ZLIB_VERSION.  Version numbers
    x.x.x.f are reserved for modifications to zlib by others than the zlib
    maintainers.  For example, if the version of the base zlib you are altering
    is "1.2.3.4", then in zlib.h you should change ZLIB_VERNUM to 0x123f, and
    ZLIB_VERSION to something like "1.2.3.f-zachary-mods-v3".  You can also
    update the version strings in deflate.c and inftrees.c.

    For altered source distributions, you should also note the origin and
    nature of the changes in zlib.h, as well as in ChangeLog and README, along
    with the dates of the alterations.  The origin should include at least your
    name (or your company's name), and an email address to contact for help or
    issues with the library.

    Note that distributing a compiled zlib library along with zlib.h and
    zconf.h is also a source distribution, and so you should change
    ZLIB_VERSION and ZLIB_VERNUM and note the origin and nature of the changes
    in zlib.h as you would for a full source distribution.

25. Will zlib work on a big-endian or little-endian architecture, and can I
    exchange compressed data between them?

    Yes and yes.

26. Will zlib work on a 64-bit machine?

    Yes.  It has been tested on 64-bit machines, and has no dependence on any
    data types being limited to 32-bits in length.  If you have any
    difficulties, please provide a complete problem report to zlib@gzip.org

27. Will zlib decompress data from the PKWare Data Compression Library?

    No.  The PKWare DCL uses a completely different compressed data format than
    does PKZIP and zlib.  However, you can look in zlib's contrib/blast
    directory for a possible solution to your problem.

28. Can I access data randomly in a compressed stream?

    No, not without some preparation.  If when compressing you periodically use
    Z_FULL_FLUSH, carefully write all the pending data at those points, and
    keep an index of those locations, then you can start decompression at those
    points.  You have to be careful to not use Z_FULL_FLUSH too often, since it
    can significantly degrade compression.  Alternatively, you can scan a
    deflate stream once to generate an index, and then use that index for
    random access.  See examples/zran.c .

29. Does zlib work on MVS, OS/390, CICS, etc.?

    It has in the past, but we have not heard of any recent evidence.  There
    were working ports of zlib 1.1.4 to MVS, but those links no longer work.
    If you know of recent, successful applications of zlib on these operating
    systems, please let us know.  Thanks.

30. Is there some simpler, easier to read version of inflate I can look at to
    understand the deflate format?

    First off, you should read RFC 1951.  Second, yes.  Look in zlib's
    contrib/puff directory.

31. Does zlib infringe on any patents?

    As far as we know, no.  In fact, that was originally the whole point behind
    zlib.  Look here for some more information:

    http://www.gzip.org/#faq11

32. Can zlib work with greater than 4 GB of data?

    Yes.  inflate() and deflate() will process any amount of data correctly.
    Each call of inflate() or deflate() is limited to input and output chunks
    of the maximum value that can be stored in the compiler's "unsigned int"
    type, but there is no limit to the number of chunks.  Note however that the
    strm.total_in and strm_total_out counters may be limited to 4 GB.  These
    counters are provided as a convenience and are not used internally by
    inflate() or deflate().  The application can easily set up its own counters
    updated after each call of inflate() or deflate() to count beyond 4 GB.
    compress() and uncompress() may be limited to 4 GB, since they operate in a
    single call.  gzseek() and gztell() may be limited to 4 GB depending on how
    zlib is compiled.  See the zlibCompileFlags() function in zlib.h.

    The word "may" appears several times above since there is a 4 GB limit only
    if the compiler's "long" type is 32 bits.  If the compiler's "long" type is
    64 bits, then the limit is 16 exabytes.

33. Does zlib have any security vulnerabilities?

    The only one that we are aware of is potentially in gzprintf().  If zlib is
    compiled to use sprintf() or vsprintf(), then there is no protection
    against a buffer overflow of an 8K string space (or other value as set by
    gzbuffer()), other than the caller of gzprintf() assuring that the output
    will not exceed 8K.  On the other hand, if zlib is compiled to use
    snprintf() or vsnprintf(), which should normally be the case, then there is
    no vulnerability.  The ./configure script will display warnings if an
    insecure variation of sprintf() will be used by gzprintf().  Also the
    zlibCompileFlags() function will return information on what variant of
    sprintf() is used by gzprintf().

    If you don't have snprintf() or vsnprintf() and would like one, you can
    find a portable implementation here:

        http://www.ijs.si/software/snprintf/

    Note that you should be using the most recent version of zlib.  Versions
    1.1.3 and before were subject to a double-free vulnerability, and versions
    1.2.1 and 1.2.2 were subject to an access exception when decompressing
    invalid compressed data.

34. Is there a Java version of zlib?

    Probably what you want is to use zlib in Java. zlib is already included
    as part of the Java SDK in the java.util.zip package. If you really want
    a version of zlib written in the Java language, look on the zlib home
    page for links: http://zlib.net/ .

35. I get this or that compiler or source-code scanner warning when I crank it
    up to maximally-pedantic. Can't you guys write proper code?

    Many years ago, we gave up attempting to avoid warnings on every compiler
    in the universe.  It just got to be a waste of time, and some compilers
    were downright silly as well as contradicted each other.  So now, we simply
    make sure that the code always works.

36. Valgrind (or some similar memory access checker) says that deflate is
    performing a conditional jump that depends on an uninitialized value.
    Isn't that a bug?

    No.  That is intentional for performance reasons, and the output of deflate
    is not affected.  This only started showing up recently since zlib 1.2.x
    uses malloc() by default for allocations, whereas earlier versions used
    calloc(), which zeros out the allocated memory.  Even though the code was
    correct, versions 1.2.4 and later was changed to not stimulate these
    checkers.

37. Will zlib read the (insert any ancient or arcane format here) compressed
    data format?

    Probably not. Look in the comp.compression FAQ for pointers to various
    formats and associated software.

38. How can I encrypt/decrypt zip files with zlib?

    zlib doesn't support encryption.  The original PKZIP encryption is very
    weak and can be broken with freely available programs.  To get strong
    encryption, use GnuPG, http://www.gnupg.org/ , which already includes zlib
    compression.  For PKZIP compatible "encryption", look at
    http://www.info-zip.org/

39. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings?

    "gzip" is the gzip format, and "deflate" is the zlib format.  They should
    probably have called the second one "zlib" instead to avoid confusion with
    the raw deflate compressed data format.  While the HTTP 1.1 RFC 2616
    correctly points to the zlib specification in RFC 1950 for the "deflate"
    transfer encoding, there have been reports of servers and browsers that
    incorrectly produce or expect raw deflate data per the deflate
    specficiation in RFC 1951, most notably Microsoft.  So even though the
    "deflate" transfer encoding using the zlib format would be the more
    efficient approach (and in fact exactly what the zlib format was designed
    for), using the "gzip" transfer encoding is probably more reliable due to
    an unfortunate choice of name on the part of the HTTP 1.1 authors.

    Bottom line: use the gzip format for HTTP 1.1 encoding.

40. Does zlib support the new "Deflate64" format introduced by PKWare?

    No.  PKWare has apparently decided to keep that format proprietary, since
    they have not documented it as they have previous compression formats.  In
    any case, the compression improvements are so modest compared to other more
    modern approaches, that it's not worth the effort to implement.

41. I'm having a problem with the zip functions in zlib, can you help?

    There are no zip functions in zlib.  You are probably using minizip by
    Giles Vollant, which is found in the contrib directory of zlib.  It is not
    part of zlib.  In fact none of the stuff in contrib is part of zlib.  The
    files in there are not supported by the zlib authors.  You need to contact
    the authors of the respective contribution for help.

42. The match.asm code in contrib is under the GNU General Public License.
    Since it's part of zlib, doesn't that mean that all of zlib falls under the
    GNU GPL?

    No.  The files in contrib are not part of zlib.  They were contributed by
    other authors and are provided as a convenience to the user within the zlib
    distribution.  Each item in contrib has its own license.

43. Is zlib subject to export controls?  What is its ECCN?

    zlib is not subject to export controls, and so is classified as EAR99.

44. Can you please sign these lengthy legal documents and fax them back to us
    so that we can use your software in our product?

    No. Go away. Shoo.
1	Frequently Asked Questions about zlib
2
3
4	If your question is not there, please check the zlib home page
5	http://zlib.net/ which may have more recent information.
6	The lastest zlib FAQ is at http://zlib.net/zlib_faq.html
7
8
9	1. Is zlib Y2K-compliant?
10
11	Yes. zlib doesn't handle dates.
12
13	2. Where can I get a Windows DLL version?
14
15	The zlib sources can be compiled without change to produce a DLL. See the
16	file win32/DLL_FAQ.txt in the zlib distribution. Pointers to the
17	precompiled DLL are found in the zlib web site at http://zlib.net/ .
18
19	3. Where can I get a Visual Basic interface to zlib?
20
21	See
22	* http://marknelson.us/1997/01/01/zlib-engine/
23	* win32/DLL_FAQ.txt in the zlib distribution
24
25	4. compress() returns Z_BUF_ERROR.
26
27	Make sure that before the call of compress(), the length of the compressed
28	buffer is equal to the available size of the compressed buffer and not
29	zero. For Visual Basic, check that this parameter is passed by reference
30	("as any"), not by value ("as long").
31
32	5. deflate() or inflate() returns Z_BUF_ERROR.
33
34	Before making the call, make sure that avail_in and avail_out are not zero.
35	When setting the parameter flush equal to Z_FINISH, also make sure that
36	avail_out is big enough to allow processing all pending input. Note that a
37	Z_BUF_ERROR is not fatal--another call to deflate() or inflate() can be
38	made with more input or output space. A Z_BUF_ERROR may in fact be
39	unavoidable depending on how the functions are used, since it is not
40	possible to tell whether or not there is more output pending when
41	strm.avail_out returns with zero. See http://zlib.net/zlib_how.html for a
42	heavily annotated example.
43
44	6. Where's the zlib documentation (man pages, etc.)?
45
46	It's in zlib.h . Examples of zlib usage are in the files example.c and
47	minigzip.c, with more in examples/ .
48
49	7. Why don't you use GNU autoconf or libtool or ...?
50
51	Because we would like to keep zlib as a very small and simple package.
52	zlib is rather portable and doesn't need much configuration.
53
54	8. I found a bug in zlib.
55
56	Most of the time, such problems are due to an incorrect usage of zlib.
57	Please try to reproduce the problem with a small program and send the
58	corresponding source to us at zlib@gzip.org . Do not send multi-megabyte
59	data files without prior agreement.
60
61	9. Why do I get "undefined reference to gzputc"?
62
63	If "make test" produces something like
64
65	example.o(.text+0x154): undefined reference to `gzputc'
66
67	check that you don't have old files libz.* in /usr/lib, /usr/local/lib or
68	/usr/X11R6/lib. Remove any old versions, then do "make install".
69
70	10. I need a Delphi interface to zlib.
71
72	See the contrib/delphi directory in the zlib distribution.
73
74	11. Can zlib handle .zip archives?
75
76	Not by itself, no. See the directory contrib/minizip in the zlib
77	distribution.
78
79	12. Can zlib handle .Z files?
80
81	No, sorry. You have to spawn an uncompress or gunzip subprocess, or adapt
82	the code of uncompress on your own.
83
84	13. How can I make a Unix shared library?
85
86	make clean
87	./configure -s
88	make
89
90	14. How do I install a shared zlib library on Unix?
91
92	After the above, then:
93
94	make install
95
96	However, many flavors of Unix come with a shared zlib already installed.
97	Before going to the trouble of compiling a shared version of zlib and
98	trying to install it, you may want to check if it's already there! If you
99	can #include <zlib.h>, it's there. The -lz option will probably link to
100	it. You can check the version at the top of zlib.h or with the
101	ZLIB_VERSION symbol defined in zlib.h .
102
103	15. I have a question about OttoPDF.
104
105	We are not the authors of OttoPDF. The real author is on the OttoPDF web
106	site: Joel Hainley, jhainley@myndkryme.com.
107
108	16. Can zlib decode Flate data in an Adobe PDF file?
109
110	Yes. See http://www.pdflib.com/ . To modify PDF forms, see
111	http://sourceforge.net/projects/acroformtool/ .
112
113	17. Why am I getting this "register_frame_info not found" error on Solaris?
114
115	After installing zlib 1.1.4 on Solaris 2.6, running applications using zlib
116	generates an error such as:
117
118	ld.so.1: rpm: fatal: relocation error: file /usr/local/lib/libz.so:
119	symbol __register_frame_info: referenced symbol not found
120
121	The symbol __register_frame_info is not part of zlib, it is generated by
122	the C compiler (cc or gcc). You must recompile applications using zlib
123	which have this problem. This problem is specific to Solaris. See
124	http://www.sunfreeware.com for Solaris versions of zlib and applications
125	using zlib.
126
127	18. Why does gzip give an error on a file I make with compress/deflate?
128
129	The compress and deflate functions produce data in the zlib format, which
130	is different and incompatible with the gzip format. The gz* functions in
131	zlib on the other hand use the gzip format. Both the zlib and gzip formats
132	use the same compressed data format internally, but have different headers
133	and trailers around the compressed data.
134
135	19. Ok, so why are there two different formats?
136
137	The gzip format was designed to retain the directory information about a
138	single file, such as the name and last modification date. The zlib format
139	on the other hand was designed for in-memory and communication channel
140	applications, and has a much more compact header and trailer and uses a
141	faster integrity check than gzip.
142
143	20. Well that's nice, but how do I make a gzip file in memory?
144
145	You can request that deflate write the gzip format instead of the zlib
146	format using deflateInit2(). You can also request that inflate decode the
147	gzip format using inflateInit2(). Read zlib.h for more details.
148
149	21. Is zlib thread-safe?
150
151	Yes. However any library routines that zlib uses and any application-
152	provided memory allocation routines must also be thread-safe. zlib's gz*
153	functions use stdio library routines, and most of zlib's functions use the
154	library memory allocation routines by default. zlib's Init functions
155	allow for the application to provide custom memory allocation routines.
156
157	Of course, you should only operate on any given zlib or gzip stream from a
158	single thread at a time.
159
160	22. Can I use zlib in my commercial application?
161
162	Yes. Please read the license in zlib.h.
163
164	23. Is zlib under the GNU license?
165
166	No. Please read the license in zlib.h.
167
168	24. The license says that altered source versions must be "plainly marked". So
169	what exactly do I need to do to meet that requirement?
170
171	You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h. In
172	particular, the final version number needs to be changed to "f", and an
173	identification string should be appended to ZLIB_VERSION. Version numbers
174	x.x.x.f are reserved for modifications to zlib by others than the zlib
175	maintainers. For example, if the version of the base zlib you are altering
176	is "1.2.3.4", then in zlib.h you should change ZLIB_VERNUM to 0x123f, and
177	ZLIB_VERSION to something like "1.2.3.f-zachary-mods-v3". You can also
178	update the version strings in deflate.c and inftrees.c.
179
180	For altered source distributions, you should also note the origin and
181	nature of the changes in zlib.h, as well as in ChangeLog and README, along
182	with the dates of the alterations. The origin should include at least your
183	name (or your company's name), and an email address to contact for help or
184	issues with the library.
185
186	Note that distributing a compiled zlib library along with zlib.h and
187	zconf.h is also a source distribution, and so you should change
188	ZLIB_VERSION and ZLIB_VERNUM and note the origin and nature of the changes
189	in zlib.h as you would for a full source distribution.
190
191	25. Will zlib work on a big-endian or little-endian architecture, and can I
192	exchange compressed data between them?
193
194	Yes and yes.
195
196	26. Will zlib work on a 64-bit machine?
197
198	Yes. It has been tested on 64-bit machines, and has no dependence on any
199	data types being limited to 32-bits in length. If you have any
200	difficulties, please provide a complete problem report to zlib@gzip.org
201
202	27. Will zlib decompress data from the PKWare Data Compression Library?
203
204	No. The PKWare DCL uses a completely different compressed data format than
205	does PKZIP and zlib. However, you can look in zlib's contrib/blast
206	directory for a possible solution to your problem.
207
208	28. Can I access data randomly in a compressed stream?
209
210	No, not without some preparation. If when compressing you periodically use
211	Z_FULL_FLUSH, carefully write all the pending data at those points, and
212	keep an index of those locations, then you can start decompression at those
213	points. You have to be careful to not use Z_FULL_FLUSH too often, since it
214	can significantly degrade compression. Alternatively, you can scan a
215	deflate stream once to generate an index, and then use that index for
216	random access. See examples/zran.c .
217
218	29. Does zlib work on MVS, OS/390, CICS, etc.?
219
220	It has in the past, but we have not heard of any recent evidence. There
221	were working ports of zlib 1.1.4 to MVS, but those links no longer work.
222	If you know of recent, successful applications of zlib on these operating
223	systems, please let us know. Thanks.
224
225	30. Is there some simpler, easier to read version of inflate I can look at to
226	understand the deflate format?
227
228	First off, you should read RFC 1951. Second, yes. Look in zlib's
229	contrib/puff directory.
230
231	31. Does zlib infringe on any patents?
232
233	As far as we know, no. In fact, that was originally the whole point behind
234	zlib. Look here for some more information:
235
236	http://www.gzip.org/#faq11
237
238	32. Can zlib work with greater than 4 GB of data?
239
240	Yes. inflate() and deflate() will process any amount of data correctly.
241	Each call of inflate() or deflate() is limited to input and output chunks
242	of the maximum value that can be stored in the compiler's "unsigned int"
243	type, but there is no limit to the number of chunks. Note however that the
244	strm.total_in and strm_total_out counters may be limited to 4 GB. These
245	counters are provided as a convenience and are not used internally by
246	inflate() or deflate(). The application can easily set up its own counters
247	updated after each call of inflate() or deflate() to count beyond 4 GB.
248	compress() and uncompress() may be limited to 4 GB, since they operate in a
249	single call. gzseek() and gztell() may be limited to 4 GB depending on how
250	zlib is compiled. See the zlibCompileFlags() function in zlib.h.
251
252	The word "may" appears several times above since there is a 4 GB limit only
253	if the compiler's "long" type is 32 bits. If the compiler's "long" type is
254	64 bits, then the limit is 16 exabytes.
255
256	33. Does zlib have any security vulnerabilities?
257
258	The only one that we are aware of is potentially in gzprintf(). If zlib is
259	compiled to use sprintf() or vsprintf(), then there is no protection
260	against a buffer overflow of an 8K string space (or other value as set by
261	gzbuffer()), other than the caller of gzprintf() assuring that the output
262	will not exceed 8K. On the other hand, if zlib is compiled to use
263	snprintf() or vsnprintf(), which should normally be the case, then there is
264	no vulnerability. The ./configure script will display warnings if an
265	insecure variation of sprintf() will be used by gzprintf(). Also the
266	zlibCompileFlags() function will return information on what variant of
267	sprintf() is used by gzprintf().
268
269	If you don't have snprintf() or vsnprintf() and would like one, you can
270	find a portable implementation here:
271
272	http://www.ijs.si/software/snprintf/
273
274	Note that you should be using the most recent version of zlib. Versions
275	1.1.3 and before were subject to a double-free vulnerability, and versions
276	1.2.1 and 1.2.2 were subject to an access exception when decompressing
277	invalid compressed data.
278
279	34. Is there a Java version of zlib?
280
281	Probably what you want is to use zlib in Java. zlib is already included
282	as part of the Java SDK in the java.util.zip package. If you really want
283	a version of zlib written in the Java language, look on the zlib home
284	page for links: http://zlib.net/ .
285
286	35. I get this or that compiler or source-code scanner warning when I crank it
287	up to maximally-pedantic. Can't you guys write proper code?
288
289	Many years ago, we gave up attempting to avoid warnings on every compiler
290	in the universe. It just got to be a waste of time, and some compilers
291	were downright silly as well as contradicted each other. So now, we simply
292	make sure that the code always works.
293
294	36. Valgrind (or some similar memory access checker) says that deflate is
295	performing a conditional jump that depends on an uninitialized value.
296	Isn't that a bug?
297
298	No. That is intentional for performance reasons, and the output of deflate
299	is not affected. This only started showing up recently since zlib 1.2.x
300	uses malloc() by default for allocations, whereas earlier versions used
301	calloc(), which zeros out the allocated memory. Even though the code was
302	correct, versions 1.2.4 and later was changed to not stimulate these
303	checkers.
304
305	37. Will zlib read the (insert any ancient or arcane format here) compressed
306	data format?
307
308	Probably not. Look in the comp.compression FAQ for pointers to various
309	formats and associated software.
310
311	38. How can I encrypt/decrypt zip files with zlib?
312
313	zlib doesn't support encryption. The original PKZIP encryption is very
314	weak and can be broken with freely available programs. To get strong
315	encryption, use GnuPG, http://www.gnupg.org/ , which already includes zlib
316	compression. For PKZIP compatible "encryption", look at
317	http://www.info-zip.org/
318
319	39. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings?
320
321	"gzip" is the gzip format, and "deflate" is the zlib format. They should
322	probably have called the second one "zlib" instead to avoid confusion with
323	the raw deflate compressed data format. While the HTTP 1.1 RFC 2616
324	correctly points to the zlib specification in RFC 1950 for the "deflate"
325	transfer encoding, there have been reports of servers and browsers that
326	incorrectly produce or expect raw deflate data per the deflate
327	specficiation in RFC 1951, most notably Microsoft. So even though the
328	"deflate" transfer encoding using the zlib format would be the more
329	efficient approach (and in fact exactly what the zlib format was designed
330	for), using the "gzip" transfer encoding is probably more reliable due to
331	an unfortunate choice of name on the part of the HTTP 1.1 authors.
332
333	Bottom line: use the gzip format for HTTP 1.1 encoding.
334
335	40. Does zlib support the new "Deflate64" format introduced by PKWare?
336
337	No. PKWare has apparently decided to keep that format proprietary, since
338	they have not documented it as they have previous compression formats. In
339	any case, the compression improvements are so modest compared to other more
340	modern approaches, that it's not worth the effort to implement.
341
342	41. I'm having a problem with the zip functions in zlib, can you help?
343
344	There are no zip functions in zlib. You are probably using minizip by
345	Giles Vollant, which is found in the contrib directory of zlib. It is not
346	part of zlib. In fact none of the stuff in contrib is part of zlib. The
347	files in there are not supported by the zlib authors. You need to contact
348	the authors of the respective contribution for help.
349
350	42. The match.asm code in contrib is under the GNU General Public License.
351	Since it's part of zlib, doesn't that mean that all of zlib falls under the
352	GNU GPL?
353
354	No. The files in contrib are not part of zlib. They were contributed by
355	other authors and are provided as a convenience to the user within the zlib
356	distribution. Each item in contrib has its own license.
357
358	43. Is zlib subject to export controls? What is its ECCN?
359
360	zlib is not subject to export controls, and so is classified as EAR99.
361
362	44. Can you please sign these lengthy legal documents and fax them back to us
363	so that we can use your software in our product?
364
365	No. Go away. Shoo.