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zlib general purpose compression library version 1.1.4
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<h1> zlib 1.1.4 Manual </h1>
<hr>
<a name="Contents"><h2>Contents</h2>
<ol type="I">
<li> <a href="#Prologue">Prologue</a>
<li> <a href="#Introduction">Introduction</a>
<li> <a href="#Utility functions">Utility functions</a>
<li> <a href="#Basic functions">Basic functions</a>
<li> <a href="#Advanced functions">Advanced functions</a>
<li> <a href="#Constants">Constants</a>
<li> <a href="#struct z_stream_s">struct z_stream_s</a>
<li> <a href="#Checksum functions">Checksum functions</a>
<li> <a href="#Misc">Misc</a>
</ol>
<hr>
<a name="Prologue"><h2> Prologue </h2>
'zlib' general purpose compression library version 1.1.4, March 11th, 2002
<p>
Copyright (C) 1995-2002 Jean-loup Gailly and Mark Adler
<p>
This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.
<p>
Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:
<ol>
<li> The origin of this software must not be misrepresented ; you must not
claim that you wrote the original software. If you use this software
in a product, an acknowledgment in the product documentation would be
appreciated but is not required.
<li> Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.
<li> This notice may not be removed or altered from any source distribution.
</ol>
<dl>
<dt>Jean-loup Gailly
<dd><a href="mailto:jloup@gzip.org">jloup@gzip.org</a>
<dt>Mark Adler
<dd><a href="mailto:madler@alumni.caltech.edu">madler@alumni.caltech.edu</a>
</dl>
The data format used by the zlib library is described by RFCs (Request for
Comments) 1950 to 1952 in the files
<a href="ftp://ds.internic.net/rfc/rfc1950.txt">
ftp://ds.internic.net/rfc/rfc1950.txt </a>
(zlib format),
<a href="ftp://ds.internic.net/rfc/rfc1951.txt">
rfc1951.txt </a>
(<a href="#deflate">deflate</a> format) and
<a href="ftp://ds.internic.net/rfc/rfc1952.txt">
rfc1952.txt </a>
(gzip format).
<p>
This manual is converted from zlib.h by
<a href="mailto:piaip@csie.ntu.edu.tw"> piaip </a>
<p>
Visit <a href="http://ftp.cdrom.com/pub/infozip/zlib/">
http://ftp.cdrom.com/pub/infozip/zlib/</a>
for the official zlib web page.
<p>
<hr>
<a name="Introduction"><h2> Introduction </h2>
The 'zlib' compression library provides in-memory compression and
decompression functions, including integrity checks of the uncompressed
data. This version of the library supports only one compression method
(deflation) but other algorithms will be added later and will have the same
stream interface.
<p>
Compression can be done in a single step if the buffers are large
enough (for example if an input file is mmap'ed), or can be done by
repeated calls of the compression function. In the latter case, the
application must provide more input and/or consume the output
(providing more output space) before each call.
<p>
The library also supports reading and writing files in gzip (.gz) format
with an interface similar to that of stdio.
<p>
The library does not install any signal handler. The decoder checks
the consistency of the compressed data, so the library should never
crash even in case of corrupted input.
<p>
<hr>
<a name="Utility functions"><h2> Utility functions </h2>
The following utility functions are implemented on top of the
<a href="#Basic functions">basic stream-oriented functions</a>.
To simplify the interface, some
default options are assumed (compression level and memory usage,
standard memory allocation functions). The source code of these
utility functions can easily be modified if you need special options.
<h3> Function list </h3>
<ul>
<li> int <a href="#compress">compress</a> (Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen);
<li> int <a href="#compress2">compress2</a> (Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen, int level);
<li> int <a href="#uncompress">uncompress</a> (Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen);
<li> typedef voidp gzFile;
<li> gzFile <a href="#gzopen">gzopen</a> (const char *path, const char *mode);
<li> gzFile <a href="#gzdopen">gzdopen</a> (int fd, const char *mode);
<li> int <a href="#gzsetparams">gzsetparams</a> (gzFile file, int level, int strategy);
<li> int <a href="#gzread">gzread</a> (gzFile file, voidp buf, unsigned len);
<li> int <a href="#gzwrite">gzwrite</a> (gzFile file, const voidp buf, unsigned len);
<li> int VA <a href="#gzprintf">gzprintf</a> (gzFile file, const char *format, ...);
<li> int <a href="#gzputs">gzputs</a> (gzFile file, const char *s);
<li> char * <a href="#gzgets">gzgets</a> (gzFile file, char *buf, int len);
<li> int <a href="#gzputc">gzputc</a> (gzFile file, int c);
<li> int <a href="#gzgetc">gzgetc</a> (gzFile file);
<li> int <a href="#gzflush">gzflush</a> (gzFile file, int flush);
<li> z_off_t <a href="#gzseek">gzseek</a> (gzFile file, z_off_t offset, int whence);
<li> z_off_t <a href="#gztell">gztell</a> (gzFile file);
<li> int <a href="#gzrewind">gzrewind</a> (gzFile file);
<li> int <a href="#gzeof">gzeof</a> (gzFile file);
<li> int <a href="#gzclose">gzclose</a> (gzFile file);
<li> const char * <a href="#gzerror">gzerror</a> (gzFile file, int *errnum);
</ul>
<h3> Function description </h3>
<dl>
<font color="Blue"><dt> int <a name="compress">compress</a> (Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen);</font>
<dd>
Compresses the source buffer into the destination buffer. sourceLen is
the byte length of the source buffer. Upon entry, destLen is the total
size of the destination buffer, which must be at least 0.1% larger than
sourceLen plus 12 bytes. Upon exit, destLen is the actual size of the
compressed buffer.<p>
This function can be used to <a href="#compress">compress</a> a whole file at once if the
input file is mmap'ed.<p>
<a href="#compress">compress</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_MEM_ERROR">Z_MEM_ERROR</a> if there was not
enough memory, <a href="#Z_BUF_ERROR">Z_BUF_ERROR</a> if there was not enough room in the output
buffer.<p>
<font color="Blue"><dt> int <a name="compress2">compress2</a> (Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen, int level);</font>
<dd>
Compresses the source buffer into the destination buffer. The level
parameter has the same meaning as in <a href="#deflateInit">deflateInit</a>. sourceLen is the byte
length of the source buffer. Upon entry, destLen is the total size of the
destination buffer, which must be at least 0.1% larger than sourceLen plus
12 bytes. Upon exit, destLen is the actual size of the compressed buffer.
<p>
<a href="#compress2">compress2</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_MEM_ERROR">Z_MEM_ERROR</a> if there was not enough
memory, <a href="#Z_BUF_ERROR">Z_BUF_ERROR</a> if there was not enough room in the output buffer,
<a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if the level parameter is invalid.
<p>
<font color="Blue"><dt> int <a name="uncompress">uncompress</a> (Bytef *dest, uLongf *destLen, const Bytef *source, uLong sourceLen);</font>
<dd>
Decompresses the source buffer into the destination buffer. sourceLen is
the byte length of the source buffer. Upon entry, destLen is the total
size of the destination buffer, which must be large enough to hold the
entire uncompressed data. (The size of the uncompressed data must have
been saved previously by the compressor and transmitted to the decompressor
by some mechanism outside the scope of this compression library.)
Upon exit, destLen is the actual size of the compressed buffer. <p>
This function can be used to decompress a whole file at once if the
input file is mmap'ed.
<p>
<a href="#uncompress">uncompress</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_MEM_ERROR">Z_MEM_ERROR</a> if there was not
enough memory, <a href="#Z_BUF_ERROR">Z_BUF_ERROR</a> if there was not enough room in the output
buffer, or <a href="#Z_DATA_ERROR">Z_DATA_ERROR</a> if the input data was corrupted.
<p>
<dt> typedef voidp gzFile;
<dd> <p>
<font color="Blue"><dt> gzFile <a name="gzopen">gzopen</a> (const char *path, const char *mode);</font>
<dd>
Opens a gzip (.gz) file for reading or writing. The mode parameter
is as in fopen ("rb" or "wb") but can also include a compression level
("wb9") or a strategy: 'f' for filtered data as in "wb6f", 'h' for
Huffman only compression as in "wb1h". (See the description
of <a href="#deflateInit2">deflateInit2</a> for more information about the strategy parameter.)
<p>
<a href="#gzopen">gzopen</a> can be used to read a file which is not in gzip format ; in this
case <a href="#gzread">gzread</a> will directly read from the file without decompression.
<p>
<a href="#gzopen">gzopen</a> returns NULL if the file could not be opened or if there was
insufficient memory to allocate the (de)compression <a href="#state">state</a> ; errno
can be checked to distinguish the two cases (if errno is zero, the
zlib error is <a href="#Z_MEM_ERROR">Z_MEM_ERROR</a>).
<p>
<font color="Blue"><dt> gzFile <a name="gzdopen">gzdopen</a> (int fd, const char *mode);</font>
<dd>
<a href="#gzdopen">gzdopen</a>() associates a gzFile with the file descriptor fd. File
descriptors are obtained from calls like open, dup, creat, pipe or
fileno (in the file has been previously opened with fopen).
The mode parameter is as in <a href="#gzopen">gzopen</a>.
<p>
The next call of <a href="#gzclose">gzclose</a> on the returned gzFile will also close the
file descriptor fd, just like fclose(fdopen(fd), mode) closes the file
descriptor fd. If you want to keep fd open, use <a href="#gzdopen">gzdopen</a>(dup(fd), mode).
<p>
<a href="#gzdopen">gzdopen</a> returns NULL if there was insufficient memory to allocate
the (de)compression <a href="#state">state</a>.
<p>
<font color="Blue"><dt> int <a name="gzsetparams">gzsetparams</a> (gzFile file, int level, int strategy);</font>
<dd>
Dynamically update the compression level or strategy. See the description
of <a href="#deflateInit2">deflateInit2</a> for the meaning of these parameters.
<p>
<a href="#gzsetparams">gzsetparams</a> returns <a href="#Z_OK">Z_OK</a> if success, or <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if the file was not
opened for writing.
<p>
<font color="Blue"><dt> int <a name="gzread">gzread</a> (gzFile file, voidp buf, unsigned len);</font>
<dd>
Reads the given number of uncompressed bytes from the compressed file.
If the input file was not in gzip format, <a href="#gzread">gzread</a> copies the given number
of bytes into the buffer.
<p>
<a href="#gzread">gzread</a> returns the number of uncompressed bytes actually read (0 for
end of file, -1 for error).
<p>
<font color="Blue"><dt> int <a name="gzwrite">gzwrite</a> (gzFile file, const voidp buf, unsigned len);</font>
<dd>
Writes the given number of uncompressed bytes into the compressed file.
<a href="#gzwrite">gzwrite</a> returns the number of uncompressed bytes actually written
(0 in case of error).
<p>
<font color="Blue"><dt> int VA <a name="gzprintf">gzprintf</a> (gzFile file, const char *format, ...);</font>
<dd>
Converts, formats, and writes the args to the compressed file under
control of the format string, as in fprintf. <a href="#gzprintf">gzprintf</a> returns the number of
uncompressed bytes actually written (0 in case of error).
<p>
<font color="Blue"><dt> int <a name="gzputs">gzputs</a> (gzFile file, const char *s);</font>
<dd>
Writes the given null-terminated string to the compressed file, excluding
the terminating null character.
<p>
<a href="#gzputs">gzputs</a> returns the number of characters written, or -1 in case of error.
<p>
<font color="Blue"><dt> char * <a name="gzgets">gzgets</a> (gzFile file, char *buf, int len);</font>
<dd>
Reads bytes from the compressed file until len-1 characters are read, or
a newline character is read and transferred to buf, or an end-of-file
condition is encountered. The string is then terminated with a null
character.
<p>
<a href="#gzgets">gzgets</a> returns buf, or <a href="#Z_NULL">Z_NULL</a> in case of error.
<p>
<font color="Blue"><dt> int <a name="gzputc">gzputc</a> (gzFile file, int c);</font>
<dd>
Writes c, converted to an unsigned char, into the compressed file.
<a href="#gzputc">gzputc</a> returns the value that was written, or -1 in case of error.
<p>
<font color="Blue"><dt> int <a name="gzgetc">gzgetc</a> (gzFile file);</font>
<dd>
Reads one byte from the compressed file. <a href="#gzgetc">gzgetc</a> returns this byte
or -1 in case of end of file or error.
<p>
<font color="Blue"><dt> int <a name="gzflush">gzflush</a> (gzFile file, int flush);</font>
<dd>
Flushes all pending output into the compressed file. The parameter
flush is as in the <a href="#deflate">deflate</a>() function. The return value is the zlib
error number (see function <a href="#gzerror">gzerror</a> below). <a href="#gzflush">gzflush</a> returns <a href="#Z_OK">Z_OK</a> if
the flush parameter is <a href="#Z_FINISH">Z_FINISH</a> and all output could be flushed.
<p>
<a href="#gzflush">gzflush</a> should be called only when strictly necessary because it can
degrade compression.
<p>
<font color="Blue"><dt> z_off_t <a name="gzseek">gzseek</a> (gzFile file, z_off_t offset, int whence);</font>
<dd>
Sets the starting position for the next <a href="#gzread">gzread</a> or <a href="#gzwrite">gzwrite</a> on the
given compressed file. The offset represents a number of bytes in the
uncompressed data stream. The whence parameter is defined as in lseek(2);
the value SEEK_END is not supported.
<p>
If the file is opened for reading, this function is emulated but can be
extremely slow. If the file is opened for writing, only forward seeks are
supported ; <a href="#gzseek">gzseek</a> then compresses a sequence of zeroes up to the new
starting position.
<p>
<a href="#gzseek">gzseek</a> returns the resulting offset location as measured in bytes from
the beginning of the uncompressed stream, or -1 in case of error, in
particular if the file is opened for writing and the new starting position
would be before the current position.
<p>
<font color="Blue"><dt> int <a name="gzrewind">gzrewind</a> (gzFile file);</font>
<dd>
Rewinds the given file. This function is supported only for reading.
<p>
<a href="#gzrewind">gzrewind</a>(file) is equivalent to (int)<a href="#gzseek">gzseek</a>(file, 0L, SEEK_SET)
<p>
<font color="Blue"><dt> z_off_t <a name="gztell">gztell</a> (gzFile file);</font>
<dd>
Returns the starting position for the next <a href="#gzread">gzread</a> or <a href="#gzwrite">gzwrite</a> on the
given compressed file. This position represents a number of bytes in the
uncompressed data stream.
<p>
<a href="#gztell">gztell</a>(file) is equivalent to <a href="#gzseek">gzseek</a>(file, 0L, SEEK_CUR)
<p>
<font color="Blue"><dt> int <a name="gzeof">gzeof</a> (gzFile file);</font>
<dd>
Returns 1 when EOF has previously been detected reading the given
input stream, otherwise zero.
<p>
<font color="Blue"><dt> int <a name="gzclose">gzclose</a> (gzFile file);</font>
<dd>
Flushes all pending output if necessary, closes the compressed file
and deallocates all the (de)compression <a href="#state">state</a>. The return value is the zlib
error number (see function <a href="#gzerror">gzerror</a> below).
<p>
<font color="Blue"><dt> const char * <a name="gzerror">gzerror</a> (gzFile file, int *errnum);</font>
<dd>
Returns the error message for the last error which occurred on the
given compressed file. errnum is set to zlib error number. If an
error occurred in the file system and not in the compression library,
errnum is set to <a href="#Z_ERRNO">Z_ERRNO</a> and the application may consult errno
to get the exact error code.
<p>
</dl>
<hr>
<a name="Basic functions"><h2> Basic functions </h2>
<h3> Function list </h3>
<ul>
<li> const char * <a href="#zlibVersion">zlibVersion</a> (void);
<li> int <a href="#deflateInit">deflateInit</a> (<a href="#z_streamp">z_streamp</a> strm, int level);
<li> int <a href="#deflate">deflate</a> (<a href="#z_streamp">z_streamp</a> strm, int flush);
<li> int <a href="#deflateEnd">deflateEnd</a> (<a href="#z_streamp">z_streamp</a> strm);
<li> int <a href="#inflateInit">inflateInit</a> (<a href="#z_streamp">z_streamp</a> strm);
<li> int <a href="#inflate">inflate</a> (<a href="#z_streamp">z_streamp</a> strm, int flush);
<li> int <a href="#inflateEnd">inflateEnd</a> (<a href="#z_streamp">z_streamp</a> strm);
</ul>
<h3> Function description </h3>
<dl>
<font color="Blue"><dt> const char * <a name="zlibVersion">zlibVersion</a> (void);</font>
<dd> The application can compare <a href="#zlibVersion">zlibVersion</a> and ZLIB_VERSION for consistency.
If the first character differs, the library code actually used is
not compatible with the zlib.h header file used by the application.
This check is automatically made by <a href="#deflateInit">deflateInit</a> and <a href="#inflateInit">inflateInit</a>.
<p>
<font color="Blue"><dt> int <a name="deflateInit">deflateInit</a> (<a href="#z_streamp">z_streamp</a> strm, int level);</font>
<dd>
Initializes the internal stream <a href="#state">state</a> for compression. The fields
<a href="#zalloc">zalloc</a>, <a href="#zfree">zfree</a> and <a href="#opaque">opaque</a> must be initialized before by the caller.
If <a href="#zalloc">zalloc</a> and <a href="#zfree">zfree</a> are set to <a href="#Z_NULL">Z_NULL</a>, <a href="#deflateInit">deflateInit</a> updates them to
use default allocation functions.
<p>
The compression level must be <a href="#Z_DEFAULT_COMPRESSION">Z_DEFAULT_COMPRESSION</a>, or between 0 and 9:
1 gives best speed, 9 gives best compression, 0 gives no compression at
all (the input data is simply copied a block at a time).
<p>
<a href="#Z_DEFAULT_COMPRESSION">Z_DEFAULT_COMPRESSION</a> requests a default compromise between speed and
compression (currently equivalent to level 6).
<p>
<a href="#deflateInit">deflateInit</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_MEM_ERROR">Z_MEM_ERROR</a> if there was not
enough memory, <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if level is not a valid compression level,
<a href="#Z_VERSION_ERROR">Z_VERSION_ERROR</a> if the zlib library version (<a href="#zlib_version">zlib_version</a>) is incompatible
with the version assumed by the caller (ZLIB_VERSION).
<a href="#msg">msg</a> is set to null if there is no error message. <a href="#deflateInit">deflateInit</a> does not
perform any compression: this will be done by <a href="#deflate">deflate</a>().
<p>
<font color="Blue"><dt> int <a name="deflate">deflate</a> (<a href="#z_streamp">z_streamp</a> strm, int flush);</font>
<dd>
<a href="#deflate">deflate</a> compresses as much data as possible, and stops when the input
buffer becomes empty or the output buffer becomes full. It may introduce some
output latency (reading input without producing any output) except when
forced to flush.<p>
The detailed semantics are as follows. <a href="#deflate">deflate</a> performs one or both of the
following actions:
<ul>
<li> Compress more input starting at <a href="#next_in">next_in</a> and update <a href="#next_in">next_in</a> and <a href="#avail_in">avail_in</a>
accordingly. If not all input can be processed (because there is not
enough room in the output buffer), <a href="#next_in">next_in</a> and <a href="#avail_in">avail_in</a> are updated and
processing will resume at this point for the next call of <a href="#deflate">deflate</a>().
<li>
Provide more output starting at <a href="#next_out">next_out</a> and update <a href="#next_out">next_out</a> and <a href="#avail_out">avail_out</a>
accordingly. This action is forced if the parameter flush is non zero.
Forcing flush frequently degrades the compression ratio, so this parameter
should be set only when necessary (in interactive applications).
Some output may be provided even if flush is not set.
</ul> <p>
Before the call of <a href="#deflate">deflate</a>(), the application should ensure that at least
one of the actions is possible, by providing more input and/or consuming
more output, and updating <a href="#avail_in">avail_in</a> or <a href="#avail_out">avail_out</a> accordingly ; <a href="#avail_out">avail_out</a>
should never be zero before the call. The application can consume the
compressed output when it wants, for example when the output buffer is full
(<a href="#avail_out">avail_out</a> == 0), or after each call of <a href="#deflate">deflate</a>(). If <a href="#deflate">deflate</a> returns <a href="#Z_OK">Z_OK</a>
and with zero <a href="#avail_out">avail_out</a>, it must be called again after making room in the
output buffer because there might be more output pending.
<p>
If the parameter flush is set to <a href="#Z_SYNC_FLUSH">Z_SYNC_FLUSH</a>, all pending output is
flushed to the output buffer and the output is aligned on a byte boundary, so
that the decompressor can get all input data available so far. (In particular
<a href="#avail_in">avail_in</a> is zero after the call if enough output space has been provided
before the call.) Flushing may degrade compression for some compression
algorithms and so it should be used only when necessary.
<p>
If flush is set to <a href="#Z_FULL_FLUSH">Z_FULL_FLUSH</a>, all output is flushed as with
<a href="#Z_SYNC_FLUSH">Z_SYNC_FLUSH</a>, and the compression <a href="#state">state</a> is reset so that decompression can
restart from this point if previous compressed data has been damaged or if
random access is desired. Using <a href="#Z_FULL_FLUSH">Z_FULL_FLUSH</a> too often can seriously degrade
the compression.
<p>
If <a href="#deflate">deflate</a> returns with <a href="#avail_out">avail_out</a> == 0, this function must be called again
with the same value of the flush parameter and more output space (updated
<a href="#avail_out">avail_out</a>), until the flush is complete (<a href="#deflate">deflate</a> returns with non-zero
<a href="#avail_out">avail_out</a>).
<p>
If the parameter flush is set to <a href="#Z_FINISH">Z_FINISH</a>, pending input is processed,
pending output is flushed and <a href="#deflate">deflate</a> returns with <a href="#Z_STREAM_END">Z_STREAM_END</a> if there
was enough output space ; if <a href="#deflate">deflate</a> returns with <a href="#Z_OK">Z_OK</a>, this function must be
called again with <a href="#Z_FINISH">Z_FINISH</a> and more output space (updated <a href="#avail_out">avail_out</a>) but no
more input data, until it returns with <a href="#Z_STREAM_END">Z_STREAM_END</a> or an error. After
<a href="#deflate">deflate</a> has returned <a href="#Z_STREAM_END">Z_STREAM_END</a>, the only possible operations on the
stream are <a href="#deflateReset">deflateReset</a> or <a href="#deflateEnd">deflateEnd</a>.
<p>
<a href="#Z_FINISH">Z_FINISH</a> can be used immediately after <a href="#deflateInit">deflateInit</a> if all the compression
is to be done in a single step. In this case, <a href="#avail_out">avail_out</a> must be at least
0.1% larger than <a href="#avail_in">avail_in</a> plus 12 bytes. If <a href="#deflate">deflate</a> does not return
<a href="#Z_STREAM_END">Z_STREAM_END</a>, then it must be called again as described above.
<p>
<a href="#deflate">deflate</a>() sets strm-> <a href="#adler">adler</a> to the <a href="#adler32">adler32</a> checksum of all input read
so far (that is, <a href="#total_in">total_in</a> bytes).
<p>
<a href="#deflate">deflate</a>() may update <a href="#data_type">data_type</a> if it can make a good guess about
the input data type (<a href="#Z_ASCII">Z_ASCII</a> or <a href="#Z_BINARY">Z_BINARY</a>). In doubt, the data is considered
binary. This field is only for information purposes and does not affect
the compression algorithm in any manner.
<p>
<a href="#deflate">deflate</a>() returns <a href="#Z_OK">Z_OK</a> if some progress has been made (more input
processed or more output produced), <a href="#Z_STREAM_END">Z_STREAM_END</a> if all input has been
consumed and all output has been produced (only when flush is set to
<a href="#Z_FINISH">Z_FINISH</a>), <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if the stream <a href="#state">state</a> was inconsistent (for example
if <a href="#next_in">next_in</a> or <a href="#next_out">next_out</a> was NULL), <a href="#Z_BUF_ERROR">Z_BUF_ERROR</a> if no progress is possible
(for example <a href="#avail_in">avail_in</a> or <a href="#avail_out">avail_out</a> was zero).
<p>
<font color="Blue"><dt> int <a name="deflateEnd">deflateEnd</a> (<a href="#z_streamp">z_streamp</a> strm);</font>
<dd>
All dynamically allocated data structures for this stream are freed.
This function discards any unprocessed input and does not flush any
pending output.
<p>
<a href="#deflateEnd">deflateEnd</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if the
stream <a href="#state">state</a> was inconsistent, <a href="#Z_DATA_ERROR">Z_DATA_ERROR</a> if the stream was freed
prematurely (some input or output was discarded). In the error case,
<a href="#msg">msg</a> may be set but then points to a static string (which must not be
deallocated).
<p>
<font color="Blue"><dt> int <a name="inflateInit">inflateInit</a> (<a href="#z_streamp">z_streamp</a> strm);</font>
<dd>
Initializes the internal stream <a href="#state">state</a> for decompression. The fields
<a href="#next_in">next_in</a>, <a href="#avail_in">avail_in</a>, <a href="#zalloc">zalloc</a>, <a href="#zfree">zfree</a> and <a href="#opaque">opaque</a> must be initialized before by
the caller. If <a href="#next_in">next_in</a> is not <a href="#Z_NULL">Z_NULL</a> and <a href="#avail_in">avail_in</a> is large enough (the exact
value depends on the compression method), <a href="#inflateInit">inflateInit</a> determines the
compression method from the zlib header and allocates all data structures
accordingly ; otherwise the allocation will be deferred to the first call of
<a href="#inflate">inflate</a>. If <a href="#zalloc">zalloc</a> and <a href="#zfree">zfree</a> are set to <a href="#Z_NULL">Z_NULL</a>, <a href="#inflateInit">inflateInit</a> updates them to
use default allocation functions.
<p>
<a href="#inflateInit">inflateInit</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_MEM_ERROR">Z_MEM_ERROR</a> if there was not enough
memory, <a href="#Z_VERSION_ERROR">Z_VERSION_ERROR</a> if the zlib library version is incompatible with the
version assumed by the caller. <a href="#msg">msg</a> is set to null if there is no error
message. <a href="#inflateInit">inflateInit</a> does not perform any decompression apart from reading
the zlib header if present: this will be done by <a href="#inflate">inflate</a>(). (So <a href="#next_in">next_in</a> and
<a href="#avail_in">avail_in</a> may be modified, but <a href="#next_out">next_out</a> and <a href="#avail_out">avail_out</a> are unchanged.)
<p>
<font color="Blue"><dt> int <a name="inflate">inflate</a> (<a href="#z_streamp">z_streamp</a> strm, int flush);</font>
<dd>
<a href="#inflate">inflate</a> decompresses as much data as possible, and stops when the input
buffer becomes empty or the output buffer becomes full. It may some
introduce some output latency (reading input without producing any output)
except when forced to flush.
<p>
The detailed semantics are as follows. <a href="#inflate">inflate</a> performs one or both of the
following actions:
<ul>
<li> Decompress more input starting at <a href="#next_in">next_in</a> and update <a href="#next_in">next_in</a> and <a href="#avail_in">avail_in</a>
accordingly. If not all input can be processed (because there is not
enough room in the output buffer), <a href="#next_in">next_in</a> is updated and processing
will resume at this point for the next call of <a href="#inflate">inflate</a>().
<li> Provide more output starting at <a href="#next_out">next_out</a> and update <a href="#next_out">next_out</a> and
<a href="#avail_out">avail_out</a> accordingly. <a href="#inflate">inflate</a>() provides as much output as possible,
until there is no more input data or no more space in the output buffer
(see below about the flush parameter).
</ul> <p>
Before the call of <a href="#inflate">inflate</a>(), the application should ensure that at least
one of the actions is possible, by providing more input and/or consuming
more output, and updating the next_* and avail_* values accordingly.
The application can consume the uncompressed output when it wants, for
example when the output buffer is full (<a href="#avail_out">avail_out</a> == 0), or after each
call of <a href="#inflate">inflate</a>(). If <a href="#inflate">inflate</a> returns <a href="#Z_OK">Z_OK</a> and with zero <a href="#avail_out">avail_out</a>, it
must be called again after making room in the output buffer because there
might be more output pending.
<p>
If the parameter flush is set to <a href="#Z_SYNC_FLUSH">Z_SYNC_FLUSH</a>, <a href="#inflate">inflate</a> flushes as much
output as possible to the output buffer. The flushing behavior of <a href="#inflate">inflate</a> is
not specified for values of the flush parameter other than <a href="#Z_SYNC_FLUSH">Z_SYNC_FLUSH</a>
and <a href="#Z_FINISH">Z_FINISH</a>, but the current implementation actually flushes as much output
as possible anyway.
<p>
<a href="#inflate">inflate</a>() should normally be called until it returns <a href="#Z_STREAM_END">Z_STREAM_END</a> or an
error. However if all decompression is to be performed in a single step
(a single call of <a href="#inflate">inflate</a>), the parameter flush should be set to
<a href="#Z_FINISH">Z_FINISH</a>. In this case all pending input is processed and all pending
output is flushed ; <a href="#avail_out">avail_out</a> must be large enough to hold all the
uncompressed data. (The size of the uncompressed data may have been saved
by the compressor for this purpose.) The next operation on this stream must
be <a href="#inflateEnd">inflateEnd</a> to deallocate the decompression <a href="#state">state</a>. The use of <a href="#Z_FINISH">Z_FINISH</a>
is never required, but can be used to inform <a href="#inflate">inflate</a> that a faster routine
may be used for the single <a href="#inflate">inflate</a>() call.
<p>
If a preset dictionary is needed at this point (see <a href="#inflateSetDictionary">inflateSetDictionary</a>
below), <a href="#inflate">inflate</a> sets strm-<a href="#adler">adler</a> to the <a href="#adler32">adler32</a> checksum of the
dictionary chosen by the compressor and returns <a href="#Z_NEED_DICT">Z_NEED_DICT</a> ; otherwise
it sets strm-> <a href="#adler">adler</a> to the <a href="#adler32">adler32</a> checksum of all output produced
so far (that is, <a href="#total_out">total_out</a> bytes) and returns <a href="#Z_OK">Z_OK</a>, <a href="#Z_STREAM_END">Z_STREAM_END</a> or
an error code as described below. At the end of the stream, <a href="#inflate">inflate</a>()
checks that its computed <a href="#adler32">adler32</a> checksum is equal to that saved by the
compressor and returns <a href="#Z_STREAM_END">Z_STREAM_END</a> only if the checksum is correct.
<p>
<a href="#inflate">inflate</a>() returns <a href="#Z_OK">Z_OK</a> if some progress has been made (more input processed
or more output produced), <a href="#Z_STREAM_END">Z_STREAM_END</a> if the end of the compressed data has
been reached and all uncompressed output has been produced, <a href="#Z_NEED_DICT">Z_NEED_DICT</a> if a
preset dictionary is needed at this point, <a href="#Z_DATA_ERROR">Z_DATA_ERROR</a> if the input data was
corrupted (input stream not conforming to the zlib format or incorrect
<a href="#adler32">adler32</a> checksum), <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if the stream structure was inconsistent
(for example if <a href="#next_in">next_in</a> or <a href="#next_out">next_out</a> was NULL), <a href="#Z_MEM_ERROR">Z_MEM_ERROR</a> if there was not
enough memory, <a href="#Z_BUF_ERROR">Z_BUF_ERROR</a> if no progress is possible or if there was not
enough room in the output buffer when <a href="#Z_FINISH">Z_FINISH</a> is used. In the <a href="#Z_DATA_ERROR">Z_DATA_ERROR</a>
case, the application may then call <a href="#inflateSync">inflateSync</a> to look for a good
compression block.
<p>
<font color="Blue"><dt> int <a name="inflateEnd">inflateEnd</a> (<a href="#z_streamp">z_streamp</a> strm);</font>
<dd>
All dynamically allocated data structures for this stream are freed.
This function discards any unprocessed input and does not flush any
pending output.
<p>
<a href="#inflateEnd">inflateEnd</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if the stream <a href="#state">state</a>
was inconsistent. In the error case, <a href="#msg">msg</a> may be set but then points to a
static string (which must not be deallocated).
</dl>
<hr>
<a name="Advanced functions"><h2> Advanced functions </h2>
The following functions are needed only in some special applications.
<h3> Function list </h3>
<ul>
<li> int <a href="#deflateInit2">deflateInit2</a> (<a href="#z_streamp">z_streamp</a> strm,
<li> int <a href="#deflateSetDictionary">deflateSetDictionary</a> (<a href="#z_streamp">z_streamp</a> strm, const Bytef *dictionary, uInt dictLength);
<li> int <a href="#deflateCopy">deflateCopy</a> (<a href="#z_streamp">z_streamp</a> dest, <a href="#z_streamp">z_streamp</a> source);
<li> int <a href="#deflateReset">deflateReset</a> (<a href="#z_streamp">z_streamp</a> strm);
<li> int <a href="#deflateParams">deflateParams</a> (<a href="#z_streamp">z_streamp</a> strm, int level, int strategy);
<li> int <a href="#inflateInit2">inflateInit2</a> (<a href="#z_streamp">z_streamp</a> strm, int windowBits);
<li> int <a href="#inflateSetDictionary">inflateSetDictionary</a> (<a href="#z_streamp">z_streamp</a> strm, const Bytef *dictionary, uInt dictLength);
<li> int <a href="#inflateSync">inflateSync</a> (<a href="#z_streamp">z_streamp</a> strm);
<li> int <a href="#inflateReset">inflateReset</a> (<a href="#z_streamp">z_streamp</a> strm);
</ul>
<h3> Function description </h3>
<dl>
<font color="Blue"><dt> int <a name="deflateInit2">deflateInit2</a> (<a href="#z_streamp">z_streamp</a> strm, int level, int method, int windowBits, int memLevel, int strategy);</font>
<dd> This is another version of <a href="#deflateInit">deflateInit</a> with more compression options. The
fields <a href="#next_in">next_in</a>, <a href="#zalloc">zalloc</a>, <a href="#zfree">zfree</a> and <a href="#opaque">opaque</a> must be initialized before by
the caller.<p>
The method parameter is the compression method. It must be <a href="#Z_DEFLATED">Z_DEFLATED</a> in
this version of the library.<p>
The windowBits parameter is the base two logarithm of the window size
(the size of the history buffer). It should be in the range 8..15 for this
version of the library. Larger values of this parameter result in better
compression at the expense of memory usage. The default value is 15 if
<a href="#deflateInit">deflateInit</a> is used instead.<p>
The memLevel parameter specifies how much memory should be allocated
for the internal compression <a href="#state">state</a>. memLevel=1 uses minimum memory but
is slow and reduces compression ratio ; memLevel=9 uses maximum memory
for optimal speed. The default value is 8. See zconf.h for total memory
usage as a function of windowBits and memLevel.<p>
The strategy parameter is used to tune the compression algorithm. Use the
value <a href="#Z_DEFAULT_STRATEGY">Z_DEFAULT_STRATEGY</a> for normal data, <a href="#Z_FILTERED">Z_FILTERED</a> for data produced by a
filter (or predictor), or <a href="#Z_HUFFMAN_ONLY">Z_HUFFMAN_ONLY</a> to force Huffman encoding only (no
string match). Filtered data consists mostly of small values with a
somewhat random distribution. In this case, the compression algorithm is
tuned to <a href="#compress">compress</a> them better. The effect of <a href="#Z_FILTERED">Z_FILTERED</a> is to force more
Huffman coding and less string matching ; it is somewhat intermediate
between Z_DEFAULT and <a href="#Z_HUFFMAN_ONLY">Z_HUFFMAN_ONLY</a>. The strategy parameter only affects
the compression ratio but not the correctness of the compressed output even
if it is not set appropriately.<p>
<a href="#deflateInit2">deflateInit2</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_MEM_ERROR">Z_MEM_ERROR</a> if there was not enough
memory, <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if a parameter is invalid (such as an invalid
method). <a href="#msg">msg</a> is set to null if there is no error message. <a href="#deflateInit2">deflateInit2</a> does
not perform any compression: this will be done by <a href="#deflate">deflate</a>().<p>
<font color="Blue"><dt> int <a name="deflateSetDictionary">deflateSetDictionary</a> (<a href="#z_streamp">z_streamp</a> strm, const Bytef *dictionary, uInt dictLength);</font>
<dd>
Initializes the compression dictionary from the given byte sequence
without producing any compressed output. This function must be called
immediately after <a href="#deflateInit">deflateInit</a>, <a href="#deflateInit2">deflateInit2</a> or <a href="#deflateReset">deflateReset</a>, before any
call of <a href="#deflate">deflate</a>. The compressor and decompressor must use exactly the same
dictionary (see <a href="#inflateSetDictionary">inflateSetDictionary</a>).<p>
The dictionary should consist of strings (byte sequences) that are likely
to be encountered later in the data to be compressed, with the most commonly
used strings preferably put towards the end of the dictionary. Using a
dictionary is most useful when the data to be compressed is short and can be
predicted with good accuracy ; the data can then be compressed better than
with the default empty dictionary.<p>
Depending on the size of the compression data structures selected by
<a href="#deflateInit">deflateInit</a> or <a href="#deflateInit2">deflateInit2</a>, a part of the dictionary may in effect be
discarded, for example if the dictionary is larger than the window size in
<a href="#deflate">deflate</a> or deflate2. Thus the strings most likely to be useful should be
put at the end of the dictionary, not at the front.<p>
Upon return of this function, strm-> <a href="#adler">adler</a> is set to the Adler32 value
of the dictionary ; the decompressor may later use this value to determine
which dictionary has been used by the compressor. (The Adler32 value
applies to the whole dictionary even if only a subset of the dictionary is
actually used by the compressor.)<p>
<a href="#deflateSetDictionary">deflateSetDictionary</a> returns <a href="#Z_OK">Z_OK</a> if success, or <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if a
parameter is invalid (such as NULL dictionary) or the stream <a href="#state">state</a> is
inconsistent (for example if <a href="#deflate">deflate</a> has already been called for this stream
or if the compression method is bsort). <a href="#deflateSetDictionary">deflateSetDictionary</a> does not
perform any compression: this will be done by <a href="#deflate">deflate</a>().<p>
<font color="Blue"><dt> int <a name="deflateCopy">deflateCopy</a> (<a href="#z_streamp">z_streamp</a> dest, <a href="#z_streamp">z_streamp</a> source);</font>
<dd>
Sets the destination stream as a complete copy of the source stream.<p>
This function can be useful when several compression strategies will be
tried, for example when there are several ways of pre-processing the input
data with a filter. The streams that will be discarded should then be freed
by calling <a href="#deflateEnd">deflateEnd</a>. Note that <a href="#deflateCopy">deflateCopy</a> duplicates the internal
compression <a href="#state">state</a> which can be quite large, so this strategy is slow and
can consume lots of memory.<p>
<a href="#deflateCopy">deflateCopy</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_MEM_ERROR">Z_MEM_ERROR</a> if there was not
enough memory, <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if the source stream <a href="#state">state</a> was inconsistent
(such as <a href="#zalloc">zalloc</a> being NULL). <a href="#msg">msg</a> is left unchanged in both source and
destination.<p>
<font color="Blue"><dt> int <a name="deflateReset">deflateReset</a> (<a href="#z_streamp">z_streamp</a> strm);</font>
<dd> This function is equivalent to <a href="#deflateEnd">deflateEnd</a> followed by <a href="#deflateInit">deflateInit</a>,
but does not free and reallocate all the internal compression <a href="#state">state</a>.
The stream will keep the same compression level and any other attributes
that may have been set by <a href="#deflateInit2">deflateInit2</a>.<p>
<a href="#deflateReset">deflateReset</a> returns <a href="#Z_OK">Z_OK</a> if success, or <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if the source
stream <a href="#state">state</a> was inconsistent (such as <a href="#zalloc">zalloc</a> or <a href="#state">state</a> being NULL).<p>
<font color="Blue"><dt> int <a name="deflateParams">deflateParams</a> (<a href="#z_streamp">z_streamp</a> strm, int level, int strategy);</font>
<dd>
Dynamically update the compression level and compression strategy. The
interpretation of level and strategy is as in <a href="#deflateInit2">deflateInit2</a>. This can be
used to switch between compression and straight copy of the input data, or
to switch to a different kind of input data requiring a different
strategy. If the compression level is changed, the input available so far
is compressed with the old level (and may be flushed); the new level will
take effect only at the next call of <a href="#deflate">deflate</a>().<p>
Before the call of <a href="#deflateParams">deflateParams</a>, the stream <a href="#state">state</a> must be set as for
a call of <a href="#deflate">deflate</a>(), since the currently available input may have to
be compressed and flushed. In particular, strm-> <a href="#avail_out">avail_out</a> must be
non-zero.<p>
<a href="#deflateParams">deflateParams</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if the source
stream <a href="#state">state</a> was inconsistent or if a parameter was invalid, <a href="#Z_BUF_ERROR">Z_BUF_ERROR</a>
if strm->avail_out was zero.<p>
<font color="Blue"><dt> int <a name="inflateInit2">inflateInit2</a> (<a href="#z_streamp">z_streamp</a> strm, int windowBits);</font>
<dd> This is another version of <a href="#inflateInit">inflateInit</a> with an extra parameter. The
fields <a href="#next_in">next_in</a>, <a href="#avail_in">avail_in</a>, <a href="#zalloc">zalloc</a>, <a href="#zfree">zfree</a> and <a href="#opaque">opaque</a> must be initialized
before by the caller.<p>
The windowBits parameter is the base two logarithm of the maximum window
size (the size of the history buffer). It should be in the range 8..15 for
this version of the library. The default value is 15 if <a href="#inflateInit">inflateInit</a> is used
instead. If a compressed stream with a larger window size is given as
input, <a href="#inflate">inflate</a>() will return with the error code <a href="#Z_DATA_ERROR">Z_DATA_ERROR</a> instead of
trying to allocate a larger window.<p>
<a href="#inflateInit2">inflateInit2</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_MEM_ERROR">Z_MEM_ERROR</a> if there was not enough
memory, <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if a parameter is invalid (such as a negative
memLevel). <a href="#msg">msg</a> is set to null if there is no error message. <a href="#inflateInit2">inflateInit2</a>
does not perform any decompression apart from reading the zlib header if
present: this will be done by <a href="#inflate">inflate</a>(). (So <a href="#next_in">next_in</a> and <a href="#avail_in">avail_in</a> may be
modified, but <a href="#next_out">next_out</a> and <a href="#avail_out">avail_out</a> are unchanged.)<p>
<font color="Blue"><dt> int <a name="inflateSetDictionary">inflateSetDictionary</a> (<a href="#z_streamp">z_streamp</a> strm, const Bytef *dictionary, uInt dictLength);</font>
<dd>
Initializes the decompression dictionary from the given uncompressed byte
sequence. This function must be called immediately after a call of <a href="#inflate">inflate</a>
if this call returned <a href="#Z_NEED_DICT">Z_NEED_DICT</a>. The dictionary chosen by the compressor
can be determined from the Adler32 value returned by this call of
<a href="#inflate">inflate</a>. The compressor and decompressor must use exactly the same
dictionary (see <a href="#deflateSetDictionary">deflateSetDictionary</a>).<p>
<a href="#inflateSetDictionary">inflateSetDictionary</a> returns <a href="#Z_OK">Z_OK</a> if success, <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if a
parameter is invalid (such as NULL dictionary) or the stream <a href="#state">state</a> is
inconsistent, <a href="#Z_DATA_ERROR">Z_DATA_ERROR</a> if the given dictionary doesn't match the
expected one (incorrect Adler32 value). <a href="#inflateSetDictionary">inflateSetDictionary</a> does not
perform any decompression: this will be done by subsequent calls of
<a href="#inflate">inflate</a>().<p>
<font color="Blue"><dt> int <a name="inflateSync">inflateSync</a> (<a href="#z_streamp">z_streamp</a> strm);</font>
<dd> Skips invalid compressed data until a full flush point (see above the
description of <a href="#deflate">deflate</a> with <a href="#Z_FULL_FLUSH">Z_FULL_FLUSH</a>) can be found, or until all
available input is skipped. No output is provided.<p>
<a href="#inflateSync">inflateSync</a> returns <a href="#Z_OK">Z_OK</a> if a full flush point has been found, <a href="#Z_BUF_ERROR">Z_BUF_ERROR</a>
if no more input was provided, <a href="#Z_DATA_ERROR">Z_DATA_ERROR</a> if no flush point has been found,
or <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if the stream structure was inconsistent. In the success
case, the application may save the current current value of <a href="#total_in">total_in</a> which
indicates where valid compressed data was found. In the error case, the
application may repeatedly call <a href="#inflateSync">inflateSync</a>, providing more input each time,
until success or end of the input data.<p>
<font color="Blue"><dt> int <a name="inflateReset">inflateReset</a> (<a href="#z_streamp">z_streamp</a> strm);</font>
<dd>
This function is equivalent to <a href="#inflateEnd">inflateEnd</a> followed by <a href="#inflateInit">inflateInit</a>,
but does not free and reallocate all the internal decompression <a href="#state">state</a>.
The stream will keep attributes that may have been set by <a href="#inflateInit2">inflateInit2</a>.
<p>
<a href="#inflateReset">inflateReset</a> returns <a href="#Z_OK">Z_OK</a> if success, or <a href="#Z_STREAM_ERROR">Z_STREAM_ERROR</a> if the source
stream <a href="#state">state</a> was inconsistent (such as <a href="#zalloc">zalloc</a> or <a href="#state">state</a> being NULL).
<p>
</dl>
<hr>
<a name="Checksum functions"><h2> Checksum functions </h2>
These functions are not related to compression but are exported
anyway because they might be useful in applications using the
compression library.
<h3> Function list </h3>
<ul>
<li> uLong <a href="#adler32">adler32</a> (uLong <a href="#adler">adler</a>, const Bytef *buf, uInt len);
<li> uLong <a href="#crc32">crc32</a> (uLong crc, const Bytef *buf, uInt len);
</ul>
<h3> Function description </h3>
<dl>
<font color="Blue"><dt> uLong <a name="adler32">adler32</a> (uLong <a href="#adler">adler</a>, const Bytef *buf, uInt len);</font>
<dd>
Update a running Adler-32 checksum with the bytes buf[0..len-1] and
return the updated checksum. If buf is NULL, this function returns
the required initial value for the checksum.
<p>
An Adler-32 checksum is almost as reliable as a CRC32 but can be computed
much faster. Usage example:
<pre>
uLong <a href="#adler">adler</a> = <a href="#adler32">adler32</a>(0L, <a href="#Z_NULL">Z_NULL</a>, 0);
while (read_buffer(buffer, length) != EOF) {
<a href="#adler">adler</a> = <a href="#adler32">adler32</a>(<a href="#adler">adler</a>, buffer, length);
}
if (<a href="#adler">adler</a> != original_adler) error();
</pre>
<font color="Blue"><dt> uLong <a name="crc32">crc32</a> (uLong crc, const Bytef *buf, uInt len);</font>
<dd>
Update a running crc with the bytes buf[0..len-1] and return the updated
crc. If buf is NULL, this function returns the required initial value
for the crc. Pre- and post-conditioning (one's complement) is performed
within this function so it shouldn't be done by the application.
Usage example:
<pre>
uLong crc = <a href="#crc32">crc32</a>(0L, <a href="#Z_NULL">Z_NULL</a>, 0);
while (read_buffer(buffer, length) != EOF) {
crc = <a href="#crc32">crc32</a>(crc, buffer, length);
}
if (crc != original_crc) error();
</pre>
</dl>
<hr>
<a name="struct z_stream_s"><h2> struct z_stream_s </h2>
<font color="Blue">
<a name="z_stream_s">
<pre>
typedef struct z_stream_s {
Bytef *<a name="next_in">next_in</a>; /* next input byte */
uInt <a name="avail_in">avail_in</a>; /* number of bytes available at <a href="#next_in">next_in</a> */
uLong <a name="total_in">total_in</a>; /* total nb of input bytes read so far */
Bytef *<a name="next_out">next_out</a>; /* next output byte should be put there */
uInt <a name="avail_out">avail_out</a>; /* remaining free space at <a href="#next_out">next_out</a> */
uLong <a name="total_out">total_out</a>; /* total nb of bytes output so far */
char *<a name="msg">msg</a>; /* last error message, NULL if no error */
struct internal_state FAR *<a name="state">state</a>; /* not visible by applications */
alloc_func <a name="zalloc">zalloc</a>; /* used to allocate the internal <a href="#state">state</a> */
free_func <a name="zfree">zfree</a>; /* used to free the internal <a href="#state">state</a> */
voidpf <a name="opaque">opaque</a>; /* private data object passed to <a href="#zalloc">zalloc</a> and <a href="#zfree">zfree</a> */
int <a name="data_type">data_type</a>; /* best guess about the data type: ascii or binary */
uLong <a name="adler">adler</a>; /* <a href="#adler32">adler32</a> value of the uncompressed data */
uLong <a name="reserved">reserved</a>; /* <a href="#reserved">reserved</a> for future use */
} <a href="#z_stream_s">z_stream</a> ;
typedef <a href="#z_stream_s">z_stream</a> FAR * <a name="z_streamp">z_streamp</a>; ÿ
</pre>
</font>
The application must update <a href="#next_in">next_in</a> and <a href="#avail_in">avail_in</a> when <a href="#avail_in">avail_in</a> has
dropped to zero. It must update <a href="#next_out">next_out</a> and <a href="#avail_out">avail_out</a> when <a href="#avail_out">avail_out</a>
has dropped to zero. The application must initialize <a href="#zalloc">zalloc</a>, <a href="#zfree">zfree</a> and
<a href="#opaque">opaque</a> before calling the init function. All other fields are set by the
compression library and must not be updated by the application. <p>
The <a href="#opaque">opaque</a> value provided by the application will be passed as the first
parameter for calls of <a href="#zalloc">zalloc</a> and <a href="#zfree">zfree</a>. This can be useful for custom
memory management. The compression library attaches no meaning to the
<a href="#opaque">opaque</a> value. <p>
<a href="#zalloc">zalloc</a> must return <a href="#Z_NULL">Z_NULL</a> if there is not enough memory for the object.
If zlib is used in a multi-threaded application, <a href="#zalloc">zalloc</a> and <a href="#zfree">zfree</a> must be
thread safe. <p>
On 16-bit systems, the functions <a href="#zalloc">zalloc</a> and <a href="#zfree">zfree</a> must be able to allocate
exactly 65536 bytes, but will not be required to allocate more than this
if the symbol MAXSEG_64K is defined (see zconf.h). WARNING: On MSDOS,
pointers returned by <a href="#zalloc">zalloc</a> for objects of exactly 65536 bytes *must*
have their offset normalized to zero. The default allocation function
provided by this library ensures this (see zutil.c). To reduce memory
requirements and avoid any allocation of 64K objects, at the expense of
compression ratio, compile the library with -DMAX_WBITS=14 (see zconf.h).
<p>
The fields <a href="#total_in">total_in</a> and <a href="#total_out">total_out</a> can be used for statistics or
progress reports. After compression, <a href="#total_in">total_in</a> holds the total size of
the uncompressed data and may be saved for use in the decompressor
(particularly if the decompressor wants to decompress everything in
a single step). <p>
<hr>
<a name="Constants"><h2> Constants </h2>
<font color="Blue">
<pre>
#define <a name="Z_NO_FLUSH">Z_NO_FLUSH</a> 0
#define <a name="Z_PARTIAL_FLUSH">Z_PARTIAL_FLUSH</a> 1
/* will be removed, use <a href="#Z_SYNC_FLUSH">Z_SYNC_FLUSH</a> instead */
#define <a name="Z_SYNC_FLUSH">Z_SYNC_FLUSH</a> 2
#define <a name="Z_FULL_FLUSH">Z_FULL_FLUSH</a> 3
#define <a name="Z_FINISH">Z_FINISH</a> 4
/* Allowed flush values ; see <a href="#deflate">deflate</a>() below for details */
#define <a name="Z_OK">Z_OK</a> 0
#define <a name="Z_STREAM_END">Z_STREAM_END</a> 1
#define <a name="Z_NEED_DICT">Z_NEED_DICT</a> 2
#define <a name="Z_ERRNO">Z_ERRNO</a> (-1)
#define <a name="Z_STREAM_ERROR">Z_STREAM_ERROR</a> (-2)
#define <a name="Z_DATA_ERROR">Z_DATA_ERROR</a> (-3)
#define <a name="Z_MEM_ERROR">Z_MEM_ERROR</a> (-4)
#define <a name="Z_BUF_ERROR">Z_BUF_ERROR</a> (-5)
#define <a name="Z_VERSION_ERROR">Z_VERSION_ERROR</a> (-6)
/* Return codes for the compression/decompression functions. Negative
* values are errors, positive values are used for special but normal events.
*/
#define <a name="Z_NO_COMPRESSION">Z_NO_COMPRESSION</a> 0
#define <a name="Z_BEST_SPEED">Z_BEST_SPEED</a> 1
#define <a name="Z_BEST_COMPRESSION">Z_BEST_COMPRESSION</a> 9
#define <a name="Z_DEFAULT_COMPRESSION">Z_DEFAULT_COMPRESSION</a> (-1)
/* compression levels */
#define <a name="Z_FILTERED">Z_FILTERED</a> 1
#define <a name="Z_HUFFMAN_ONLY">Z_HUFFMAN_ONLY</a> 2
#define <a name="Z_DEFAULT_STRATEGY">Z_DEFAULT_STRATEGY</a> 0
/* compression strategy ; see <a href="#deflateInit2">deflateInit2</a>() below for details */
#define <a name="Z_BINARY">Z_BINARY</a> 0
#define <a name="Z_ASCII">Z_ASCII</a> 1
#define <a name="Z_UNKNOWN">Z_UNKNOWN</a> 2
/* Possible values of the <a href="#data_type">data_type</a> field */
#define <a name="Z_DEFLATED">Z_DEFLATED</a> 8
/* The <a href="#deflate">deflate</a> compression method (the only one supported in this version) */
#define <a name="Z_NULL">Z_NULL</a> 0 /* for initializing <a href="#zalloc">zalloc</a>, <a href="#zfree">zfree</a>, <a href="#opaque">opaque</a> */
#define <a name="zlib_version">zlib_version</a> <a href="#zlibVersion">zlibVersion</a>()
/* for compatibility with versions less than 1.0.2 */
</pre>
</font>
<hr>
<a name="Misc"><h2> Misc </h2>
<a href="#deflateInit">deflateInit</a> and <a href="#inflateInit">inflateInit</a> are macros to allow checking the zlib version
and the compiler's view of <a href="#z_stream_s">z_stream</a>.
<p>
Other functions:
<dl>
<font color="Blue"><dt> const char * <a name="zError">zError</a> (int err);</font>
<font color="Blue"><dt> int <a name="inflateSyncPoint">inflateSyncPoint</a> (<a href="#z_streamp">z_streamp</a> z);</font>
<font color="Blue"><dt> const uLongf * <a name="get_crc_table">get_crc_table</a> (void);</font>
</dl>
<hr>
<font size="-1">
Last update: Wed Oct 13 20:42:34 1999<br>
piapi@csie.ntu.edu.tw
</font>
</body>
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