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