MirOS Manual: adler32_combine(3), compress(3), compress2(3), compressBound(3), crc32(3), crc32_combine(3), deflate(3), deflateBound(3), deflateCopy(3), deflateEnd(3), deflateInit(3), deflateInit2(3), deflateParams(3), deflatePrime(3), deflateReset(3), deflateSetDictionary(3), deflateSetHeader(3), deflateTune(3), gzclearerr(3), gzclose(3), gzdirect(3), gzdopen(3), gzeof(3), gzerror(3), gzflush(3), gzgetc(3), gzgets(3), gzopen(3), gzprintf(3), gzputc(3), gzputs(3), gzread(3), gzrewind(3), gzseek(3), gzsetparams(3), gztell(3), gzungetc(3), gzwrite(3), inflate(3), inflateBack(3), inflateBackEnd(3), inflateBackInit(3), inflateCopy(3), inflateEnd(3), inflateGetHeader(3), inflateInit(3), inflateInit2(3), inflatePrime(3), inflateReset(3), inflateSetDictionary(3), inflateSync(3), uncompress(3), zlibCompileFlags(3), zlibVersion(3)

COMPRESS(3)                BSD Programmer's Manual                 COMPRESS(3)

NAME

     compress - zlib general purpose compression library

SYNOPSIS

     #include <zlib.h>

     Basic functions

     const char *
     zlibVersion(void);

     int
     deflateInit(z_streamp strm, int level);

     int
     deflate(z_streamp strm, int flush);

     int
     deflateEnd(z_streamp strm);

     int
     inflateInit(z_streamp strm);

     int
     inflate(z_streamp strm, int flush);

     int
     inflateEnd(z_streamp strm);

     Advanced functions

     int
     deflateInit2(z_streamp strm, int level, int method, int windowBits,
             int memLevel, int strategy);

     int
     deflateSetDictionary(z_streamp strm, const Bytef *dictionary,
             uInt dictLength);

     int
     deflateCopy(z_streamp dest, z_streamp source);

     int
     deflateReset(z_streamp strm);

     int
     deflateParams(z_streamp strm, int level, int strategy);

     int
     deflateTune(z_streamp strm, int good_length, int max_lazy,
             int nice_length, int max_chain);

     uLong
     deflateBound(z_streamp strm, uLong sourceLen);

     int
     deflatePrime(z_streamp strm, int bits, int value);

     int
     deflateSetHeader(z_streamp strm, gz_headerp head);

     int
     inflateInit2(z_streamp strm, int windowBits);

     int
     inflateSetDictionary(z_streamp strm, const Bytef *dictionary,
             uInt dictLength);

     int
     inflateSync(z_streamp strm);

     int
     inflateCopy(z_streamp dst, z_streamp source);

     int
     inflateReset(z_streamp strm);

     int
     inflatePrime(z_streamp strm, int bits, int value);

     int
     inflateGetHeader(z_streamp strm, gz_headerp head);

     int
     inflateBackInit(z_stream *strm, int windowBits,
             unsigned char FAR *window);

     int
     inflateBack(z_stream *strm, in_func in, void FAR *in_desc, out_func out,
             void FAR *out_desc);

     int
     inflateBackEnd(z_stream *strm);

     uLong
     zlibCompileFlags(void);

     Utility functions

     typedef voidp gzFile;

     int
     compress(Bytef *dest, uLongf *destLen, const Bytef *source,
             uLong sourceLen);

     int
     compress2(Bytef *dest, uLongf *destLen, const Bytef *source,
             uLong sourceLen, int level);

     uLong
     compressBound(uLong sourceLen);

     int
     uncompress(Bytef *dest, uLongf *destLen, const Bytef *source,
             uLong sourceLen);

     gzFile
     gzopen(const char *path, const char *mode);

     gzFile
     gzdopen(int fd, const char *mode);

     int
     gzsetparams(gzFile file, int level, int strategy);

     int
     gzread(gzFile file, voidp buf, unsigned len);

     int
     gzwrite(gzFile file, voidpc buf, unsigned len);

     int
     gzprintf(gzFile file, const char *format, ...);

     int
     gzputs(gzFile file, const char *s);

     char *
     gzgets(gzFile file, char *buf, int len);

     int
     gzputc(gzFile file, int c);

     int
     gzgetc(gzFile file);

     int
     gzungetc(int c, gzFile file);

     int
     gzflush(gzFile file, int flush);

     z_off_t
     gzseek(gzFile file, z_off_t offset, int whence);

     int
     gzrewind(gzFile file);

     z_off_t
     gztell(gzFile file);

     int
     gzeof(gzFile file);

     int
     gzdirect(gzFile file);

     int
     gzclose(gzFile file);

     const char *
     gzerror(gzFile file, int *errnum);

     void
     gzclearerr(gzFile file);

     Checksum functions

     uLong
     adler32(uLong adler, const Bytef *buf, uInt len);

     uLong
     adler32_combine(uLong adler1, uLong adler2, z_off_t len2);

     uLong
     crc32(uLong crc, const Bytef *buf, uInt len);

     uLong
     crc32_combine(uLong crc1, uLong crc2, z_off_t len2);

DESCRIPTION

     This manual page describes the zlib general purpose compression library,
     version 1.2.3.

     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.

     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.

     The compressed data format used by default by the in-memory functions is
     the zlib format, which is a zlib wrapper documented in RFC 1950, wrapped
     around a deflate stream, which is itself documented in RFC 1951.

     The library also supports reading and writing files in gzip(1) (.gz) for-
     mat with an interface similar to that of stdio(3) using the functions
     that start with "gz". The gzip format is different from the zlib format.
     gzip is a gzip wrapper, documented in RFC 1952, wrapped around a deflate
     stream. This library can optionally read and write gzip streams in memory
     as well.

     The zlib format was designed to be compact and fast for use in memory and
     on communications channels. The gzip format was designed for single-file
     compression on file systems, has a larger header than zlib to maintain
     directory information, and uses a different, slower, check method than
     zlib.

     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.

     The functions within the library are divided into the following sections:

           -   Basic functions
           -   Advanced functions
           -   Utility functions
           -   Checksum functions

BASIC FUNCTIONS

     const char * zlibVersion(void);

             The application can compare zlibVersion() and ZLIB_VERSION for
             consistency. If the first character differs, the library code ac-
             tually used is not compatible with the <zlib.h> header file used
             by the application. This check is automatically made by defla-
             teInit() and inflateInit().

     int deflateInit(z_streamp strm, int level);

             The deflateInit() function initializes the internal stream state
             for compression. The fields zalloc, zfree, and opaque must be in-
             itialized before by the caller. If zalloc and zfree are set to
             Z_NULL, deflateInit() updates them to use default allocation
             functions.

             The compression level must be Z_DEFAULT_COMPRESSION, 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).

             Z_DEFAULT_COMPRESSION requests a default compromise between speed
             and compression (currently equivalent to level 6).

             deflateInit() returns Z_OK if successful, Z_MEM_ERROR if there
             was not enough memory, Z_STREAM_ERROR if level is not a valid
             compression level, Z_VERSION_ERROR if the zlib library version
             (zlib_version) is incompatible with the version assumed by the
             caller (ZLIB_VERSION). msg is set to null if there is no error
             message. deflateInit() does not perform any compression: this
             will be done by deflate().

     int deflate(z_streamp strm, int flush);

             deflate() 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.

             The detailed semantics are as follows. deflate() performs one or
             both of the following actions:

             Compress more input starting at next_in and update next_in and
             avail_in accordingly. If not all input can be processed (because
             there is not enough room in the output buffer), next_in and
             avail_in are updated and processing will resume at this point for
             the next call to deflate().

             Provide more output starting at next_out and update next_out and
             avail_out accordingly. This action is forced if the parameter
             flush is non-zero. Forcing flush frequently degrades the compres-
             sion ratio, so this parameter should be set only when necessary
             (in interactive applications). Some output may be provided even
             if flush is not set.

             Before the call to deflate(), the application should ensure that
             at least one of the actions is possible, by providing more input
             and/or consuming more output, and updating avail_in or avail_out
             accordingly; avail_out 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 (avail_out == 0), or after
             each call to deflate(). If deflate() returns Z_OK and with zero
             avail_out, it must be called again after making room in the out-
             put buffer because there might be more output pending.

             Normally the parameter flush is set to Z_NO_FLUSH, which allows
             deflate() to decide how much data to accumulate before producing
             output, in order to maximise compression.

             If the parameter flush is set to Z_SYNC_FLUSH, 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, avail_in is zero after the call
             if enough output space has been provided before the call.) Flush-
             ing may degrade compression for some compression algorithms and
             so it should be used only when necessary.

             If flush is set to Z_FULL_FLUSH, all output is flushed as with
             Z_SYNC_FLUSH, and the compression state is reset so that
             decompression can restart from this point if previous compressed
             data has been damaged or if random access is desired. Using
             Z_FULL_FLUSH too often can seriously degrade compression.

             If deflate() returns with avail_out == 0, this function must be
             called again with the same value of the flush parameter and more
             output space (updated avail_out), until the flush is complete
             (deflate() returns with non-zero avail_out). In the case of a
             Z_FULL_FLUSH or a Z_SYNC_FLUSH, make sure that avail_out is
             greater than six to avoid repeated flush markers due to avail_out
             == 0 on return.

             If the parameter flush is set to Z_FINISH, pending input is pro-
             cessed, pending output is flushed and deflate() returns with
             Z_STREAM_END if there was enough output space; if deflate() re-
             turns with Z_OK, this function must be called again with Z_FINISH
             and more output space (updated avail_out but no more input data,
             until it returns with Z_STREAM_END or an error. After deflate()
             has returned Z_STREAM_END, the only possible operations on the
             stream are deflateReset() or deflateEnd().

             Z_FINISH can be used immediately after deflateInit() if all the
             compression is to be done in a single step. In this case,
             avail_out must be at least the value returned by deflateBound()
             (see below). If deflate() does not return Z_STREAM_END, then it
             must be called again as described above.

             deflate() sets strm->adler to the Adler-32 checksum of all input
             read so far (that is, total_in bytes).

             deflate() may update strm->data_type if it can make a good guess
             about the input data type (Z_BINARY or Z_TEXT). If in doubt, the
             data is considered binary. This field is only for information
             purposes and does not affect the compression algorithm in any
             manner.

             deflate() returns Z_OK if some progress has been made (more input
             processed or more output produced), Z_STREAM_END if all input has
             been consumed and all output has been produced (only when flush
             is set to Z_FINISH), Z_STREAM_ERROR if the stream state was in-
             consistent (for example, if next_in or next_out was NULL),
             Z_BUF_ERROR if no progress is possible (for example, avail_in or
             avail_out was zero). Note that Z_BUF_ERROR is not fatal, and de-
             flate() can be called again with more input and more output space
             to continue processing.

     int deflateEnd(z_streamp strm);

             All dynamically allocated data structures for this stream are
             freed. This function discards any unprocessed input and does not
             flush any pending output.

             deflateEnd() returns Z_OK if successful, Z_STREAM_ERROR if the
             stream state was inconsistent, Z_DATA_ERROR if the stream was
             freed prematurely (some input or output was discarded). In the
             error case, msg may be set but then points to a static string
             (which must not be deallocated).

     int inflateInit(z_streamp strm);
             The inflateInit() function initializes the internal stream state
             for decompression. The fields next_in, avail_in, zalloc, zfree,
             and opaque must be initialized before by the caller. If next_in
             is not Z_NULL and avail_in is large enough (the exact value
             depends on the compression method), inflateInit() determines the
             compression method from the zlib header and allocates all data
             structures accordingly; otherwise the allocation will be deferred
             to the first call to inflate(). If zalloc and zfree are set to
             Z_NULL, inflateInit() updates them to use default allocation
             functions.

             inflateInit() returns Z_OK if successful, Z_MEM_ERROR if there
             was not enough memory, Z_VERSION_ERROR if the zlib library ver-
             sion is incompatible with the version assumed by the caller. msg
             is set to null if there is no error message. inflateInit() does
             not perform any decompression apart from reading the zlib header
             if present: this will be done by inflate(). (So next_in and
             avail_in may be modified, but next_out and avail_out are un-
             changed.)

     int inflate(z_streamp strm, int flush);
             inflate() decompresses 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.

             The detailed semantics are as follows. inflate() performs one or
             both of the following actions:

             Decompress more input starting at next_in and update next_in and
             avail_in accordingly. If not all input can be processed (because
             there is not enough room in the output buffer), next_in is updat-
             ed and processing will resume at this point for the next call to
             inflate().

             Provide more output starting at next_out and update next_out and
             avail_out accordingly. inflate() provides as much output as pos-
             sible, until there is no more input data or no more space in the
             output buffer (see below about the flush parameter).

             Before the call to inflate(), 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
             (avail_out == 0), or after each call to inflate(). If inflate()
             returns Z_OK and with zero avail_out, it must be called again
             after making room in the output buffer because there might be
             more output pending.

             The flush parameter of inflate() can be Z_NO_FLUSH, Z_SYNC_FLUSH,
             Z_FINISH, or Z_BLOCK. Z_SYNC_FLUSH requests that inflate() flush
             as much output as possible to the output buffer. Z_BLOCK requests
             that inflate() stop if and when it gets to the next deflate block
             boundary. When decoding the zlib or gzip format, this will cause
             inflate() to return immediately after the header and before the
             first block. When doing a raw inflate, inflate() will go ahead
             and process the first block, and will return when it gets to the
             end of that block, or when it runs out of data.

             The Z_BLOCK option assists in appending to or combining deflate
             streams. Also to assist in this, on return inflate() will set
             strm->data_type to the number of unused bits in the last byte
             taken from strm->next_in, plus 64 if inflate() is currently
             decoding the last block in the deflate stream, plus 128 if in-
             flate() returned immediately after decoding an end-of-block code
             or decoding the complete header up to just before the first byte
             of the deflate stream. The end-of-block will not be indicated un-
             til all of the uncompressed data from that block has been written
             to strm->next_out. The number of unused bits may in general be
             greater than seven, except when bit 7 of data_type is set, in
             which case the number of unused bits will be less than eight.

             inflate() should normally be called until it returns Z_STREAM_END
             or an error. However if all decompression is to be performed in a
             single step (a single call to inflate), the parameter flush
             should be set to Z_FINISH. In this case all pending input is pro-
             cessed and all pending output is flushed; avail_out must be large
             enough to hold all the uncompressed data. (The size of the un-
             compressed data may have been saved by the compressor for this
             purpose.) The next operation on this stream must be inflateEnd()
             to deallocate the decompression state. The use of Z_FINISH is
             never required, but can be used to inform inflate() that a faster
             approach may be used for the single inflate() call.

             In this implementation, inflate() always flushes as much output
             as possible to the output buffer, and always uses the faster ap-
             proach on the first call. So the only effect of the flush parame-
             ter in this implementation is on the return value of inflate(),
             as noted below, or when it returns early because Z_BLOCK is used.

             If a preset dictionary is needed after this call (see infla-
             teSetDictionary() below), inflate() sets strm->adler to the
             Adler-32 checksum of the dictionary chosen by the compressor and
             returns Z_NEED_DICT; otherwise it sets strm->adler to the Adler-
             32 checksum of all output produced so far (that is, total_out
             bytes) and returns Z_OK, Z_STREAM_END or an error code as
             described below. At the end of the stream, inflate() checks that
             its computed Adler-32 checksum is equal to that saved by the
             compressor and returns Z_STREAM_END only if the checksum is
             correct.

             inflate() will decompress and check either zlib-wrapped or gzip-
             wrapped deflate data. The header type is detected automatically.
             Any information contained in the gzip header is not retained, so
             applications that need that information should instead use raw
             inflate; see inflateInit2() below, or inflateBack() and perform
             their own processing of the gzip header and trailer.

             inflate() returns Z_OK if some progress has been made (more input
             processed or more output produced), Z_STREAM_END if the end of
             the compressed data has been reached and all uncompressed output
             has been produced, Z_NEED_DICT if a preset dictionary is needed
             at this point, Z_DATA_ERROR if the input data was corrupted (in-
             put stream not conforming to the zlib format or incorrect check
             value), Z_STREAM_ERROR if the stream structure was inconsistent
             (for example, if next_in or next_out was NULL), Z_MEM_ERROR if
             there was not enough memory, Z_BUF_ERROR if no progress is possi-
             ble or if there was not enough room in the output buffer when
             Z_FINISH is used. Note that Z_BUF_ERROR is not fatal, and in-
             flate() can be called again with more input and more output space
             to continue compressing. If Z_DATA_ERROR is returned, the appli-
             cation may then call inflateSync() to look for a good compression
             block if a partial recovery of the data is desired.

     int inflateEnd(z_streamp strm);
             All dynamically allocated data structures for this stream are
             freed. This function discards any unprocessed input and does not
             flush any pending output.

             inflateEnd() returns Z_OK if successful, or Z_STREAM_ERROR if the
             stream state was inconsistent. In the error case, msg may be set
             but then points to a static string (which must not be
             deallocated).

ADVANCED FUNCTIONS

     The following functions are needed only in some special applications.

     int deflateInit2(z_streamp strm, int level, int method, int windowBits,
             int memLevel, int strategy);

             This is another version of deflateInit() with more compression
             options. The fields next_in, zalloc, zfree, and opaque must be
             initialized before by the caller.

             The method parameter is the compression method. It must be
             Z_DEFLATED in this version of the library.

             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 deflateInit() is used instead.

             windowBits can also be -8..-15 for raw deflate. In this case,
             -windowBits determines the window size. deflate() will then gen-
             erate raw deflate data with no zlib header or trailer, and will
             not compute an Adler-32 check value.

             windowBits can also be greater than 15 for optional gzip encod-
             ing. Add 16 to windowBits to write a simple gzip header and
             trailer around the compressed data instead of a zlib wrapper. The
             gzip header will have no file name, no extra data, no comment, no
             modification time (set to zero), no header crc, and the operating
             system will be set to 255 (unknown). If a gzip stream is being
             written, strm->adler is a crc32 instead of an adler32.

             The memLevel parameter specifies how much memory should be allo-
             cated for the internal compression state. 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.

             The strategy parameter is used to tune the compression algorithm.
             Use the value Z_DEFAULT_STRATEGY for normal data; Z_FILTERED for
             data produced by a filter (or predictor); Z_HUFFMAN_ONLY to force
             Huffman encoding only (no string match), or Z_RLE to limit match
             distances to one (run-length encoding). Filtered data consists
             mostly of small values with a somewhat random distribution. In
             this case, the compression algorithm is tuned to compress them
             better. The effect of Z_FILTERED is to force more Huffman coding
             and less string matching; it is somewhat intermediate between
             Z_DEFAULT and Z_HUFFMAN_ONLY. Z_RLE is designed to be almost as
             fast as Z_HUFFMAN_ONLY, but gives better compression for PNG im-
             age data. The strategy parameter only affects the compression ra-
             tio but not the correctness of the compressed output, even if it
             is not set appropriately. Z_FIXED prevents the use of dynamic
             Huffman codes, allowing for a simpler decoder for special appli-
             cations.

             deflateInit2() returns Z_OK if successful, Z_MEM_ERROR if there
             was not enough memory, Z_STREAM_ERROR if a parameter is invalid
             (such as an invalid method). msg is set to null if there is no
             error message. deflateInit2() does not perform any compression:
             this will be done by deflate().

     int deflateSetDictionary(z_streamp strm, const Bytef *dictionary, uInt
             dictLength);

             Initializes the compression dictionary from the given byte se-
             quence without producing any compressed output. This function
             must be called immediately after deflateInit(), deflateInit2(),
             or deflateReset(), before any call to deflate(). The compressor
             and decompressor must use exactly the same dictionary (see
             inflateSetDictionary()).

             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 ac-
             curacy; the data can then be compressed better than with the de-
             fault empty dictionary.

             Depending on the size of the compression data structures selected
             by deflateInit() or deflateInit2(), a part of the dictionary may
             in effect be discarded, for example if the dictionary is larger
             than the window size in deflate() or deflate2(). Thus the strings
             most likely to be useful should be put at the end of the diction-
             ary, not at the front. In addition, the current implementation of
             deflate() will use at most the window size minus 262 bytes of the
             provided dictionary.

             Upon return of this function, strm->adler is set to the Adler-32
             value of the dictionary; the decompressor may later use this
             value to determine which dictionary has been used by the compres-
             sor. (The Adler-32 value applies to the whole dictionary even if
             only a subset of the dictionary is actually used by the compres-
             sor.) If a raw deflate was requested, then the Adler-32 value is
             not computed and strm->adler is not set.

             deflateSetDictionary() returns Z_OK if successful, or
             Z_STREAM_ERROR if a parameter is invalid (such as NULL
             dictionary) or the stream state is inconsistent (for example if
             deflate() has already been called for this stream or if the
             compression method is bsort). deflateSetDictionary() does not
             perform any compression: this will be done by deflate().

     int deflateCopy(z_streamp dest, z_streamp source);

             The deflateCopy() function sets the destination stream as a com-
             plete copy of the source stream.

             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 deflateEnd(). Note that
             deflateCopy() duplicates the internal compression state which can
             be quite large, so this strategy is slow and can consume lots of
             memory.

             deflateCopy() returns Z_OK if successful, Z_MEM_ERROR if there
             was not enough memory, Z_STREAM_ERROR if the source stream state
             was inconsistent (such as zalloc being NULL). msg is left un-
             changed in both source and destination.

     int deflateReset(z_streamp strm);

             This function is equivalent to deflateEnd() followed by defla-
             teInit(), but does not free and reallocate all the internal
             compression state. The stream will keep the same compression lev-
             el and any other attributes that may have been set by deflateIn-
             it2().

             deflateReset() returns Z_OK if successful, or Z_STREAM_ERROR if
             the source stream state was inconsistent (such as zalloc or state
             being NULL).

     int deflateParams(z_streamp strm, int level, int strategy);

             The deflateParams() function dynamically updates the compression
             level and compression strategy. The interpretation of level and
             strategy is as in deflateInit2(). 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 avail-
             able so far is compressed with the old level (and may be
             flushed); the new level will take effect only at the next call to
             deflate().

             Before the call to deflateParams(), the stream state must be set
             as for a call to deflate(), since the currently available input
             may have to be compressed and flushed. In particular, strm-
             >avail_out must be non-zero.

             deflateParams() returns Z_OK if successful, Z_STREAM_ERROR if the
             source stream state was inconsistent or if a parameter was in-
             valid, or Z_BUF_ERROR if strm->avail_out was zero.

     int deflateTune(z_streamp strm, int good_length, int max_lazy, int
             nice_length, int max_chain)

             Fine tune deflate()'s internal compression parameters. This
             should only be used by someone who understands the algorithm used
             by zlib's deflate for searching for the best matching string, and
             even then only by the most fanatic optimizer trying to squeeze
             out the last compressed bit for their specific input data. Read
             the deflate.c source code for the meaning of the max_lazy,
             good_length, nice_length, and max_chain parameters.

             deflateTune() can be called after deflateInit() or deflateIn-
             it2(), and returns Z_OK on success, or Z_STREAM_ERROR for an in-
             valid deflate stream.

     uLong deflateBound(z_streamp strm, uLong sourceLen)

             deflateBound() returns an upper bound on the compressed size
             after deflation of sourceLen bytes. It must be called after de-
             flateInit() or deflateInit2(). This would be used to allocate an
             output buffer for deflation in a single pass, and so would be
             called before deflate().

     int deflatePrime(z_streamp strm, int bits, int value)

             deflatePrime() inserts bits in the deflate output stream. The in-
             tent is that this function is used to start off the deflate out-
             put with the bits leftover from a previous deflate stream when
             appending to it. As such, this function can only be used for raw
             deflate, and must be used before the first deflate() call after a
             deflateInit2() or deflateReset(). bits must be less than or equal
             to 16, and that many of the least significant bits of value will
             be inserted in the output.

             deflatePrime() returns Z_OK if successful, or Z_STREAM_ERROR if
             the source stream state was inconsistent.

     int deflateSetHeader(z_streamp strm, gz_headerp head)

             deflateSetHeader() provides gzip header information for when a
             gzip stream is requested by deflateInit2(). deflateSetHeader()
             may be called after deflateInit2() or deflateReset() and before
             the first call of deflate(). The text, time, os, extra field,
             name, and comment information in the provided gz_header structure
             are written to the gzip header (xflag is ignored - the extra
             flags are set according to the compression level). The caller
             must assure that, if not Z_NULL, name and comment are terminated
             with a zero byte, and that if extra is not Z_NULL, that extra_len
             bytes are available there. If hcrc is true, a gzip header CRC is
             included. Note that the current versions of the command-line ver-
             sion of gzip(1) do not support header CRCs, and will report that
             it is a "multi-part gzip file" and give up.

             If deflateSetHeader() is not used, the default gzip header has
             text false, the time set to zero, and os set to 255, with no ex-
             tra, name, or comment fields. The gzip header is returned to the
             default state by deflateReset().

             deflateSetHeader() returns Z_OK if successful, or Z_STREAM_ERROR
             if the source stream state was inconsistent.

     int inflateInit2(z_streamp strm, int windowBits);

             This is another version of inflateInit() with an extra parameter.
             The fields next_in, avail_in, zalloc, zfree, and opaque must be
             initialized before by the caller.

             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 inflateInit() is used instead. windowBits must be greater
             than or equal to the windowBits value provided to deflateInit2()
             while compressing, or it must be equal to 15 if deflateInit2()
             was not used. If a compressed stream with a larger window size is
             given as input, inflate() will return with the error code
             Z_DATA_ERROR instead of trying to allocate a larger window.

             windowBits can also be -8..-15 for raw inflate. In this case,
             -windowBits determines the window size. inflate() will then pro-
             cess raw deflate data, not looking for a zlib or gzip header, not
             generating a check value, and not looking for any check values
             for comparison at the end of the stream. This is for use with
             other formats that use the deflate compressed data format such as
             zip. Those formats provide their own check values. If a custom
             format is developed using the raw deflate format for compressed
             data, it is recommended that a check value such as an Adler-32 or
             a crc32 be applied to the uncompressed data as is done in the
             zlib, gzip, and zip formats. For most applications, the zlib for-
             mat should be used as is. Note that comments above on the use in
             deflateInit2() applies to the magnitude of windowBits.

             windowBits can also be greater than 15 for optional gzip decod-
             ing. Add 32 to windowBits to enable zlib and gzip decoding with
             automatic header detection, or add 16 to decode only the gzip
             format (the zlib format will return a Z_DATA_ERROR). If a gzip
             stream is being decoded, strm->adler is a crc32 instead of an
             adler32.

             inflateInit2() returns Z_OK if successful, Z_MEM_ERROR if there
             was not enough memory, Z_STREAM_ERROR if a parameter is invalid
             (such as a null strm). msg is set to null if there is no error
             message. inflateInit2() does not perform any decompression apart
             from reading the zlib header if present: this will be done by in-
             flate(). (So next_in and avail_in may be modified, but next_out
             and avail_out are unchanged.)

     int inflateSetDictionary(z_streamp strm, const Bytef *dictionary, uInt
             dictLength);

             Initializes the decompression dictionary from the given un-
             compressed byte sequence. This function must be called immediate-
             ly after a call to inflate() if that call returned Z_NEED_DICT.
             The dictionary chosen by the compressor can be determined from
             the Adler-32 value returned by that call to inflate(). The
             compressor and decompressor must use exactly the same dictionary
             (see deflateSetDictionary()). For raw inflate, this function can
             be called immediately after inflateInit2() or inflateReset() and
             before any call to inflate() to set the dictionary. The applica-
             tion must ensure that the dictionary that was used for compres-
             sion is provided.

             inflateSetDictionary() returns Z_OK if successful, Z_STREAM_ERROR
             if a parameter is invalid (such as NULL dictionary) or the stream
             state is inconsistent, Z_DATA_ERROR if the given dictionary
             doesn't match the expected one (incorrect Adler-32 value). infla-
             teSetDictionary() does not perform any decompression: this will
             be done by subsequent calls of inflate().

     int inflateSync(z_streamp strm);

             Skips invalid compressed data until a full flush point (see above
             the description of deflate() with Z_FULL_FLUSH) can be found, or
             until all available input is skipped. No output is provided.

             inflateSync() returns Z_OK if a full flush point has been found,
             Z_BUF_ERROR if no more input was provided, Z_DATA_ERROR if no
             flush point has been found, or Z_STREAM_ERROR if the stream
             structure was inconsistent. In the success case, the application
             may save the current value of total_in which indicates where
             valid compressed data was found. In the error case, the applica-
             tion may repeatedly call inflateSync(), providing more input each
             time, until success or end of the input data.

     int inflateCopy(z_streamp dest, z_streamp source)

             Sets the destination stream as a complete copy of the source
             stream.

             This function can be useful when randomly accessing a large
             stream. The first pass through the stream can periodically record
             the inflate state, allowing restarting inflate at those points
             when randomly accessing the stream.

             inflateCopy() returns Z_OK if success, Z_MEM_ERROR if there was
             not enough memory, Z_STREAM_ERROR if the source stream state was
             inconsistent (such as zalloc being NULL). msg is left unchanged
             in both source and dest.

     int inflateReset(z_streamp strm);

             This function is equivalent to inflateEnd() followed by infla-
             teInit(), but does not free and reallocate all the internal
             decompression state. The stream will keep attributes that may
             have been set by inflateInit2().

             inflateReset() returns Z_OK if successful, or Z_STREAM_ERROR if
             the source stream state was inconsistent (such as zalloc or state
             being NULL).

     int inflatePrime(z_stream strm, int bits, int value)

             This function inserts bits in the inflate input stream. The in-
             tent is that this function is used to start inflating at a bit
             position in the middle of a byte. The provided bits will be used
             before any bytes are used from next_in. This function should only
             be used with raw inflate, and should be used before the first in-
             flate() call after inflateInit2() or inflateReset(). bits must be
             less than or equal to 16, and that many of the least significant
             bits of value will be inserted in the input.

             inflatePrime() returns Z_OK if successful, or Z_STREAM_ERROR if
             the source stream state was inconsistent.

     int inflateGetHeader(z_streamp strm, gz_headerp head)

             inflateGetHeader() requests that gzip header information be
             stored in the provided gz_header structure. inflateGetHeader()
             may be called after inflateInit2() or inflateReset(), and before
             the first call of inflate(). As inflate() processes the gzip
             stream, head->done is zero until the header is completed, at
             which time head->done is set to one. If a zlib stream is being
             decoded, then head->done is set to -1 to indicate that there will
             be no gzip header information forthcoming. Note that Z_BLOCK can
             be used to force inflate() to return immediately after header
             processing is complete and before any actual data is
             decompressed.

             The text, time, xflags, and os fields are filled in with the gzip
             header contents. hcrc is set to true if there is a header CRC.
             (The header CRC was valid if done is set to one.) If extra is not
             Z_NULL, then extra_max contains the maximum number of bytes to
             write to extra. Once done is true, extra_len contains the actual
             extra field length, and extra contains the extra field, or that
             field truncated if extra_max is less than extra_len. If name is
             not Z_NULL, then up to name_max characters are written there,
             terminated with a zero unless the length is greater than
             name_max. If comment is not Z_NULL, then up to comm_max charac-
             ters are written there, terminated with a zero unless the length
             is greater than comm_max. When any of extra, name, or comment are
             not Z_NULL and the respective field is not present in the header,
             then that field is set to Z_NULL to signal its absence. This al-
             lows the use of deflateSetHeader() with the returned structure to
             duplicate the header. However if those fields are set to allocat-
             ed memory, then the application will need to save those pointers
             elsewhere so that they can be eventually freed.

             If inflateGetHeader() is not used, then the header information is
             simply discarded. The header is always checked for validity, in-
             cluding the header CRC if present. inflateReset() will reset the
             process to discard the header information. The application would
             need to call inflateGetHeader() again to retrieve the header from
             the next gzip stream.

             inflateGetHeader() returns Z_OK if successful, or Z_STREAM_ERROR
             if the source stream state was inconsistent.

     int inflateBackInit(z_stream *strm, int windowBits, unsigned char FAR
             *window)

             Initialize the internal stream state for decompression using in-
             flateBack() calls. The fields zalloc, zfree and opaque in strm
             must be initialized before the call. If zalloc and zfree are
             Z_NULL, then the default library-derived memory allocation rou-
             tines are used. windowBits is the base two logarithm of the win-
             dow size, in the range 8..15. window is a caller supplied buffer
             of that size. Except for special applications where it is assured
             that deflate() was used with small window sizes, windowBits must
             be 15 and a 32K byte window must be supplied to be able to
             decompress general deflate streams.

             See inflateBack() for the usage of these routines.

             inflateBackInit() will return Z_OK on success, Z_STREAM_ERROR if
             any of the parameters are invalid, Z_MEM_ERROR if the internal
             state could not be allocated, or Z_VERSION_ERROR if the version
             of the library does not match the version of the header file.

     int inflateBack(z_stream *strm, in_func in, void FAR *in_desc, out_func
             out, void FAR *out_desc)

             inflateBack() does a raw inflate with a single call using a
             call-back interface for input and output. This is more efficient
             than inflate() for file I/O applications in that it avoids copy-
             ing between the output and the sliding window by simply making
             the window itself the output buffer. This function trusts the ap-
             plication to not change the output buffer passed by the output
             function, at least until inflateBack() returns.

             inflateBackInit() must be called first to allocate the internal
             state and to initialize the state with the user-provided window
             buffer. inflateBack() may then be used multiple times to inflate
             a complete, raw deflate stream with each call. inflateBackEnd()
             is then called to free the allocated state.

             A raw deflate stream is one with no zlib or gzip header or
             trailer. This routine would normally be used in a utility that
             reads zip or gzip files and writes out uncompressed files. The
             utility would decode the header and process the trailer on its
             own, hence this routine expects only the raw deflate stream to
             decompress. This is different from the normal behavior of in-
             flate(), which expects either a zlib or gzip header and trailer
             around the deflate stream.

             inflateBack() uses two subroutines supplied by the caller that
             are then called by inflateBack() for input and output. inflate-
             Back() calls those routines until it reads a complete deflate
             stream and writes out all of the uncompressed data, or until it
             encounters an error. The function's parameters and return types
             are defined above in the in_func and out_func typedefs. inflate-
             Back() will call in(in_desc, &buf) which should return the number
             of bytes of provided input, and a pointer to that input in buf.
             If there is no input available, in() must return zero - buf is
             ignored in that case - and inflateBack() will return a buffer er-
             ror. inflateBack() will call out(out_desc, buf, len) to write the
             uncompressed data buf[0..len-1]. out() should return zero on suc-
             cess, or non-zero on failure. If out() returns non-zero, inflate-
             Back() will return with an error. Neither in() nor out() are per-
             mitted to change the contents of the window provided to infla-
             teBackInit(), which is also the buffer that out() uses to write
             from. The length written by out() will be at most the window
             size. Any non-zero amount of input may be provided by in().

             For convenience, inflateBack() can be provided input on the first
             call by setting strm->next_in and strm->avail_in. If that input
             is exhausted, then in() will be called. Therefore strm->next_in
             must be initialized before calling inflateBack(). If strm-
             >next_in is Z_NULL, then in() will be called immediately for in-
             put. If strm->next_in is not Z_NULL, then strm->avail_in must
             also be initialized, and then if strm->avail_in is not zero, in-
             put will initially be taken from strm->next_in[0 .. strm-
             >avail_in - 1].

             The in_desc and out_desc parameters of inflateBack() are passed
             as the first parameter of in() and out() respectively when they
             are called. These descriptors can be optionally used to pass any
             information that the caller-supplied in() and out() functions
             need to do their job.

             On return, inflateBack() will set strm->next_in and strm-
             >avail_in to pass back any unused input that was provided by the
             last in() call. The return values of inflateBack() can be
             Z_STREAM_END on success, Z_BUF_ERROR if in() or out() returned an
             error, Z_DATA_ERROR if there was a format error in the deflate
             stream (in which case strm->msg is set to indicate the nature of
             the error), or Z_STREAM_ERROR if the stream was not properly ini-
             tialized. In the case of Z_BUF_ERROR, an input or output error
             can be distinguished using strm->next_in which will be Z_NULL
             only if in() returned an error. If strm->next is not Z_NULL, then
             the Z_BUF_ERROR was due to out() returning non-zero. (in() will
             always be called before out(), so strm->next_in is assured to be
             defined if out() returns non-zero.) Note that inflateBack() can-
             not return Z_OK.

     int inflateBackEnd(z_stream *strm)

             All memory allocated by inflateBackInit() is freed.

             inflateBackEnd() returns Z_OK on success, or Z_STREAM_ERROR if
             the stream state was inconsistent.

     uLong zlibCompileFlags(void)

             This function returns flags indicating compile-time options.

             Type sizes, two bits each:

                   00      16 bits
                   01      32 bits
                   10      64 bits
                   11      other:

                                 1.0     size of uInt
                                 3.2     size of uLong
                                 5.4     size of voidpf (pointer)
                                 7.6     size of z_off_t

             Compiler, assembler, and debug options:

                   8       DEBUG
                   9       ASMV or ASMINF - use ASM code
                   10      ZLIB_WINAPI - exported functions use the WINAPI
                           calling convention
                   11      0 (reserved)

             One-time table building (smaller code, but not thread-safe if
             true):

                   12      BUILDFIXED -- build static block decoding tables
                           when needed
                   13      DYNAMIC_CRC_TABLE -- build CRC calculation tables
                           when needed
                   14,15   0 (reserved)

             Library content (indicates missing functionality):

                   16      NO_GZCOMPRESS - gz* functions cannot compress (to
                           avoid linking deflate code when not needed)
                   17      NO_GZIP - deflate can't write gzip streams, and in-
                           flate can't detect and decode gzip streams (to
                           avoid linking CRC code)
                   18-19   0 (reserved)

             Operation variations (changes in library functionality):

                   20      PKZIP_BUG_WORKAROUND - slightly more permissive in-
                           flate
                   21      FASTEST - deflate algorithm with only one, lowest
                           compression level
                   22,23   0 (reserved)

             The sprintf variant used by gzprintf (zero is best):

                   24      0 = vs*, 1 = s* - 1 means limited to 20 arguments
                           after the format
                   25      0 = *nprintf, 1 = *printf - 1 means gzprintf() not
                           secure!
                   26      0 = returns value, 1 = void - 1 means inferred
                           string length returned

             Remainder:

                   27-31   0 (reserved)

UTILITY FUNCTIONS

     The following utility functions are implemented on top of the basic
     stream-oriented functions. To simplify the interface, some default op-
     tions 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.

     int compress(Bytef *dest, uLongf *destLen, const Bytef *source, uLong
             sourceLen);

             The compress() function 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 the value returned by
             compressBound(sourcelen). Upon exit, destLen is the actual size
             of the compressed buffer. This function can be used to compress a
             whole file at once if the input file is mmap'ed.

             compress() returns Z_OK if successful, Z_MEM_ERROR if there was
             not enough memory, or Z_BUF_ERROR if there was not enough room in
             the output buffer.

     int compress2(Bytef *dest, uLongf *destLen, const Bytef *source, uLong
             sourceLen, int level);

             The compress2() function compresses the source buffer into the
             destination buffer. The level parameter has the same meaning as
             in deflateInit(). 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 the value returned by
             compressBound(sourceLen). Upon exit, destLen is the actual size
             of the compressed buffer.

             compress2() returns Z_OK if successful, Z_MEM_ERROR if there was
             not enough memory, Z_BUF_ERROR if there was not enough room in
             the output buffer, or Z_STREAM_ERROR if the level parameter is
             invalid.

     int compressBound(uLong sourceLen)

             compressBound() returns an upper bound on the compressed size
             after compress() or compress2() on sourceLen bytes. It would be
             used before a compress() or compress2() call to allocate the des-
             tination buffer.

     int uncompress(Bytef *dest, uLongf *destLen, const Bytef *source, uLong
             sourceLen);

             The uncompress() function 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 un-
             compressed 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 compres-
             sion library.) Upon exit, destLen is the actual size of the
             compressed buffer. This function can be used to decompress a
             whole file at once if the input file is mmap'ed.

             uncompress() returns Z_OK if successful, Z_MEM_ERROR if there was
             not enough memory, Z_BUF_ERROR if there was not enough room in
             the output buffer, or Z_DATA_ERROR if the input data was corrupt-
             ed or incomplete.

     gzFile gzopen(const char *path, const char *mode);

             The gzopen() function opens a gzip (.gz) file for reading or
             writing. The mode parameter is as in fopen(3) ("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", or 'R' for run-length encoding as in "wb1R". (See the
             description of deflateInit2() for more information about the
             strategy parameter.)

             gzopen() can be used to read a file which is not in gzip format;
             in this case gzread() will directly read from the file without
             decompression.

             gzopen() returns NULL if the file could not be opened or if there
             was insufficient memory to allocate the (de)compression state;
             errno can be checked to distinguish the two cases (if errno is
             zero, the zlib error is Z_MEM_ERROR).

     gzFile gzdopen(int fd, const char *mode);

             The gzdopen() function associates a gzFile with the file descrip-
             tor fd. File descriptors are obtained from calls like open(2),
             dup(2), creat(3), pipe(2), or fileno(3) (if the file has been
             previously opened with fopen(3)). The mode parameter is as in
             gzopen().

             The next call to gzclose() 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
             gzdopen(dup(fd), mode).

             gzdopen() returns NULL if there was insufficient memory to allo-
             cate the (de)compression state.

     int gzsetparams(gzFile file, int level, int strategy);

             The gzsetparams() function dynamically updates the compression
             level or strategy. See the description of deflateInit2() for the
             meaning of these parameters.

             gzsetparams() returns Z_OK if successful, or Z_STREAM_ERROR if
             the file was not opened for writing.

     int gzread(gzFile file, voidp buf, unsigned len);

             The gzread() function reads the given number of uncompressed
             bytes from the compressed file. If the input file was not in gzip
             format, gzread() copies the given number of bytes into the
             buffer.

             gzread() returns the number of uncompressed bytes actually read
             (0 for end of file, -1 for error).

     int gzwrite(gzFile file, voidpc buf, unsigned len);

             The gzwrite() function writes the given number of uncompressed
             bytes into the compressed file. gzwrite() returns the number of
             uncompressed bytes actually written (0 in case of error).

     int gzprintf(gzFile file, const char *format, ...);

             The gzprintf() function converts, formats, and writes the args to
             the compressed file under control of the format string, as in
             fprintf(3). gzprintf() returns the number of uncompressed bytes
             actually written (0 in case of error). The number of uncompressed
             bytes written is limited to 4095. The caller should make sure
             that this limit is not exceeded. If it is exceeded, then
             gzprintf() will return an error (0) with nothing written. In this
             case, there may also be a buffer overflow with unpredictable
             consequences, which is possible only if zlib was compiled with
             the insecure functions sprintf() or vsprintf() because the secure
             snprintf() or vsnprintf() functions were not available.

     int gzputs(gzFile file, const char *s);

             The gzputs() function writes the given null-terminated string to
             the compressed file, excluding the terminating null character.

             gzputs() returns the number of characters written, or -1 in case
             of error.

     char * gzgets(gzFile file, char *buf, int len);

             The gzgets() function 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.

             gzgets() returns buf, or Z_NULL in case of error.

     int gzputc(gzFile file, int c);

             The gzputc() function writes c, converted to an unsigned char,
             into the compressed file. gzputc() returns the value that was
             written, or -1 in case of error.

     int gzgetc(gzFile file);

             The gzgetc() function reads one byte from the compressed file.
             gzgetc() returns this byte or -1 in case of end of file or error.

     int gzungetc(int c, gzFile file)

             Push one character back onto the stream to be read again later.
             Only one character of push-back is allowed. gzungetc() returns
             the character pushed, or -1 on failure. gzungetc() will fail if a
             character has been pushed but not read yet, or if c is -1. The
             pushed character will be discarded if the stream is repositioned
             with gzseek() or gzrewind().

     int gzflush(gzFile file, int flush);

             The gzflush() function flushes all pending output into the
             compressed file. The parameter flush is as in the deflate() func-
             tion. The return value is the zlib error number (see function
             gzerror() below). gzflush() returns Z_OK if the flush parameter
             is Z_FINISH and all output could be flushed.

             gzflush() should be called only when strictly necessary because
             it can degrade compression.

     z_off_t gzseek(gzFile file, z_off_t offset, int whence);

             Sets the starting position for the next gzread() or gzwrite() 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.

             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; gzseek() then compresses a sequence
             of zeroes up to the new starting position.

             gzseek() 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 posi-
             tion.

     int gzrewind(gzFile file);

             The gzrewind() function rewinds the given file. This function is
             supported only for reading.

             gzrewind(file) is equivalent to (int)gzseek(file, 0L, SEEK_SET).

     z_off_t gztell(gzFile file);

             The gztell() function returns the starting position for the next
             gzread() or gzwrite() on the given compressed file. This position
             represents a number of bytes in the uncompressed data stream.

             gztell(file) is equivalent to gzseek(file, 0L, SEEK_CUR).

     int gzeof(gzFile file);

             The gzeof() function returns 1 when EOF has previously been
             detected reading the given input stream, otherwise zero.

     int gzdirect(gzFile file);

             The gzdirect() function returns 1 if the file is being read
             directly without compression; otherwise it returns 0.

     int gzclose(gzFile file);

             The gzclose() function flushes all pending output if necessary,
             closes the compressed file and deallocates all the
             (de)compression state. The return value is the zlib error number
             (see function gzerror() below).

     const char * gzerror(gzFile file, int *errnum);

             The gzerror() function returns the error message for the last er-
             ror which occurred on the given compressed file. errnum is set to
             the zlib error number. If an error occurred in the file system
             and not in the compression library, errnum is set to Z_ERRNO and
             the application may consult errno to get the exact error code.

     void gzclearerr(gzFile file)
             Clears the error and end-of-file flags for file. This is analo-
             gous to the clearerr() function in stdio. This is useful for con-
             tinuing to read a gzip file that is being written concurrently.

CHECKSUM FUNCTIONS

     These functions are not related to compression but are exported anyway
     because they might be useful in applications using the compression li-
     brary.

     uLong adler32(uLong adler, const Bytef *buf, uInt len);
             The adler32() function updates a running Adler-32 checksum with
             the bytes buf[0..len-1] and returns the updated checksum. If buf
             is NULL, this function returns the required initial value for the
             checksum.

             An Adler-32 checksum is almost as reliable as a CRC32 but can be
             computed much faster. Usage example:

                   uLong adler = adler32(0L, Z_NULL, 0);

                   while (read_buffer(buffer, length) != EOF) {
                   adler = adler32(adler, buffer, length);
                   }
                   if (adler != original_adler) error();

     uLong adler32_combine(uLong adler1, uLong adler2, z_off_t len2)

             The adler32_combine() function combines two Adler-32 checksums
             into one. For two sequences of bytes, seq1 and seq2 with lengths
             len1 and len2, Adler-32 checksums are calculated for each, adler1
             and adler2. adler32_combine() returns the Adler-32 checksum of
             seq1 and seq2 concatenated, requiring only adler1, adler2, and
             len2.

     uLong crc32(uLong crc, const Bytef *buf, uInt len);

             The crc32() function updates a running CRC-32 with the bytes
             buf[0..len-1] and returns the updated CRC-32. 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:

                   uLong crc = crc32(0L, Z_NULL, 0);

                   while (read_buffer(buffer, length) != EOF) {
                   crc = crc32(crc, buffer, length);
                   }
                   if (crc != original_crc) error();

     uLong crc32_combine(uLong crc1, uLong crc2, z_off_t len2)

             The crc32_combine() function combines two CRC-32 check values
             into one. For two sequences of bytes, seq1 and seq2 with lengths
             len1 and len2, CRC-32 check values are calculated for each, crc1
             and crc2. crc32_combine() returns the CRC-32 check value of seq1
             and seq2 concatenated, requiring only crc1, crc2, and len2.

STRUCTURES

     struct internal_state;

     typedef struct z_stream_s {
         Bytef    *next_in;  /* next input byte */
         uInt     avail_in;  /* number of bytes available at next_in */
         off_t    total_in;  /* total nb of input bytes read so far */

         Bytef    *next_out; /* next output byte should be put there */
         uInt     avail_out; /* remaining free space at next_out */
         off_t    total_out; /* total nb of bytes output so far */

         char     *msg;      /* last error message, NULL if no error */
         struct internal_state FAR *state; /* not visible by applications */

         alloc_func zalloc;  /* used to allocate the internal state */
         free_func  zfree;   /* used to free the internal state */
         voidpf     opaque;  /* private data object passed to zalloc and zfree*/

         int     data_type;  /* best guess about the data type: binary or text*/
         uLong   adler;      /* adler32 value of the uncompressed data */
         uLong   reserved;   /* reserved for future use */
     } z_stream;

     typedef z_stream FAR * z_streamp;

     /*
          gzip header information passed to and from zlib routines.
       See RFC 1952 for more details on the meanings of these fields.
     */
     typedef struct gz_header_s {
         int     text;       /* true if compressed data believed to be text */
         uLong   time;       /* modification time */
         int     xflags;     /*extra flags (not used when writing a gzip file)*/
         int     os;         /* operating system */
         Bytef   *extra;     /* pointer to extra field or Z_NULL if none */
         uInt    extra_len;  /* extra field length (valid if extra != Z_NULL) */
         uInt    extra_max;  /* space at extra (only when reading header) */
         Bytef   *name;      /* pointer to zero-terminated file name or Z_NULL*/
         uInt    name_max;   /* space at name (only when reading header) */
         Bytef   *comment;   /* pointer to zero-terminated comment or Z_NULL */
         uInt    comm_max;   /* space at comment (only when reading header) */
         int     hcrc;       /* true if there was or will be a header crc */
         int     done;       /* true when done reading gzip header (not used
                                when writing a gzip file) */
     } gz_header;

     typedef gz_header FAR *gz_headerp;

     The application must update next_in and avail_in when avail_in has
     dropped to zero. It must update next_out and avail_out when avail_out has
     dropped to zero. The application must initialize zalloc, zfree, and
     opaque before calling the init function. All other fields are set by the
     compression library and must not be updated by the application.

     The opaque value provided by the application will be passed as the first
     parameter for calls to zalloc() and zfree(). This can be useful for cus-
     tom memory management. The compression library attaches no meaning to the
     opaque value.

     zalloc must return Z_NULL if there is not enough memory for the object.
     If zlib is used in a multi-threaded application, zalloc and zfree must be
     thread safe.

     On 16-bit systems, the functions zalloc and zfree must be able to allo-
     cate exactly 65536 bytes, and more (for Unix).

     The fields total_in and total_out can be used for statistics or progress
     reports. After compression, total_in holds the total size of the un-
     compressed data and may be saved for use in the decompressor (particular-
     ly if the decompressor wants to decompress everything in a single step).

CONSTANTS

     #define Z_NO_FLUSH      0
     #define Z_PARTIAL_FLUSH 1 /* will be removed, use Z_SYNC_FLUSH instead */
     #define Z_SYNC_FLUSH    2
     #define Z_FULL_FLUSH    3
     #define Z_FINISH        4
     #define Z_BLOCK          5
     /* Allowed flush values; see deflate() and inflate() below for details */

     #define Z_OK            0
     #define Z_STREAM_END    1
     #define Z_NEED_DICT     2
     #define Z_ERRNO        (-1)
     #define Z_STREAM_ERROR (-2)
     #define Z_DATA_ERROR   (-3)
     #define Z_MEM_ERROR    (-4)
     #define Z_BUF_ERROR    (-5)
     #define Z_VERSION_ERROR (-6)
     /* Return codes for the compression/decompression functions.
      * Negative values are errors,
      * positive values are used for special but normal events.
      */

     #define Z_NO_COMPRESSION         0
     #define Z_BEST_SPEED             1
     #define Z_BEST_COMPRESSION       9
     #define Z_DEFAULT_COMPRESSION  (-1)
     /* compression levels */

     #define Z_FILTERED            1
     #define Z_HUFFMAN_ONLY        2
     #define Z_RLE                 3
     #define Z_FIXED               4
     #define Z_DEFAULT_STRATEGY    0
     /* compression strategy; see deflateInit2() below for details */

     #define Z_BINARY   0
     #define Z_TEXT     1
     #define Z_ASCII    Z_TEXT /* for compatibility with 1.2.2 and earlier */
     #define Z_UNKNOWN  2
     /* Possible values of the data_type field (though see inflate()) */

     #define Z_DEFLATED   8
     /* The deflate compression method
      * (the only one supported in this version)
     */

     #define Z_NULL  0  /* for initializing zalloc, zfree, opaque */

     #define zlib_version zlibVersion()
     /* for compatibility with versions < 1.0.2 */

VARIOUS HACKS

     deflateInit and inflateInit are macros to allow checking the zlib version
     and the compiler's view of z_stream.

     int deflateInit_(z_stream strm, int level, const char *version, int
             stream_size);

     int inflateInit_(z_stream strm, const char *version, int stream_size);

     int deflateInit2_(z_stream strm, int level, int method, int windowBits,
             int memLevel, int strategy, const char *version, int stream_size)

     int inflateInit2_(z_stream strm, int windowBits, const char *version, int
             stream_size);

     int inflateBackInit_(z_stream *strm, int windowBits, unsigned char FAR
             *window, const char *version, int stream_size)

     const char * zError(int err);

     int inflateSyncPoint(z_streamp z);

     const uLongf * get_crc_table(void);

SEE ALSO

     compress(1), gzip(1)

     http://www.zlib.net/

STANDARDS

     P. Deutsch and J-L. Gailly, ZLIB Compressed Data Format Specification
     version 3.3, RFC 1950, May 1996.

     P. Deutsch, DEFLATE Compressed Data Format Specification version 1.3, RFC
     1951, May 1996.

     P. Deutsch, GZIP file format specification version 4.3, RFC 1952, May
     1996.

HISTORY

     This manual page is based on an HTML version of <zlib.h> converted by
     piaip <piaip@csie.ntu.edu.tw> and was converted to mdoc format by the
     OpenBSD project.

AUTHORS

     Jean-loup Gailly <jloup@gzip.org>
     Mark Adler <madler@alumni.caltech.edu>

MirOS BSD #10-current           August 5, 2013                              23

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