104 lines
4.2 KiB
TeX
104 lines
4.2 KiB
TeX
\section{Built-in Module \sectcode{zlib}}
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\label{module-zlib}
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\bimodindex{zlib}
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For applications that require data compression, the functions in this
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module allow compression and decompression, using the zlib library,
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which is based on GNU zip. The zlib library has its own home page at
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\code{http://www.cdrom.com/pub/infozip/zlib/}.
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Version 1.0.4 is the most recent version as of April 30, 1997; use a
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later version if one is available.
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The available functions in this module are:
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\renewcommand{\indexsubitem}{(in module zlib)}
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\begin{funcdesc}{adler32}{string\optional{\, value}}
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Computes a Adler-32 checksum of \var{string}. (An Adler-32
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checksum is almost as reliable as a CRC32 but can be computed much
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more quickly.) If \var{value} is present, it is used as the
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starting value of the checksum; otherwise, a fixed default value is
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used. This allows computing a running checksum over the
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concatenation of several input strings. The algorithm is not
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cryptographically strong, and should not be used for
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authentication or digital signatures.
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\end{funcdesc}
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\begin{funcdesc}{compress}{string\optional{\, level}}
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Compresses the data in \var{string}, returning a string contained
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compressed data. \var{level} is an integer from 1 to 9 controlling
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the level of compression; 1 is fastest and produces the least
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compression, 9 is slowest and produces the most. The default value is
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6. Raises the \code{zlib.error} exception if any error occurs.
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\end{funcdesc}
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\begin{funcdesc}{compressobj}{\optional{level}}
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Returns a compression object, to be used for compressing data streams
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that won't fit into memory at once. \var{level} is an integer from
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1 to 9 controlling the level of compression; 1 is fastest and
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produces the least compression, 9 is slowest and produces the most.
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The default value is 6.
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\end{funcdesc}
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\begin{funcdesc}{crc32}{string\optional{\, value}}
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Computes a CRC (Cyclic Redundancy Check) sum of \var{string}. If
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\var{value} is present, it is used as the starting value of the
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checksum; otherwise, a fixed default value is used. This allows
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computing a running checksum over the concatenation of several
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input strings. The algorithm is not cryptographically strong, and
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should not be used for authentication or digital signatures.
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\end{funcdesc}
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\begin{funcdesc}{decompress}{string}
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Decompresses the data in \var{string}, returning a string containing
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the uncompressed data. Raises the \code{zlib.error} exception if any
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error occurs.
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\end{funcdesc}
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\begin{funcdesc}{decompressobj}{\optional{wbits}}
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Returns a compression object, to be used for decompressing data streams
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that won't fit into memory at once. The \var{wbits} parameter
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controls the size of the window buffer; usually this can be left
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alone.
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\end{funcdesc}
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Compression objects support the following methods:
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\begin{funcdesc}{compress}{string}
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Compress \var{string}, returning a string containing compressed data
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for at least part of the data in \var{string}. This data should be
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concatenated to the output produced by any preceding calls to the
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\code{compress()} method. Some input may be kept in internal buffers
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for later processing.
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\end{funcdesc}
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\begin{funcdesc}{flush}{}
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All pending input is processed, and an string containing the remaining
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compressed output is returned. After calling \code{flush()}, the
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\code{compress()} method cannot be called again; the only realistic
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action is to delete the object.
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\end{funcdesc}
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Decompression objects support the following methods:
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\begin{funcdesc}{decompress}{string}
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Decompress \var{string}, returning a string containing the
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uncompressed data corresponding to at least part of the data in
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\var{string}. This data should be concatenated to the output produced
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by any preceding calls to the
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\code{decompress()} method. Some of the input data may be preserved
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in internal buffers for later processing.
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\end{funcdesc}
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\begin{funcdesc}{flush}{}
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All pending input is processed, and a string containing the remaining
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uncompressed output is returned. After calling \code{flush()}, the
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\code{decompress()} method cannot be called again; the only realistic
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action is to delete the object.
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\end{funcdesc}
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\begin{seealso}
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\seemodule{gzip}{reading and writing \file{gzip}-format files}
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\end{seealso}
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