NAME

 
Compress - utility class for compressing/decompressing FITS files

SYNOPSIS

 
class Compress {
protected:

public:
    enum CompressType {
        NO_COMPRESS,            // no compression
        UNIX_COMPRESS,          // Compressed FITS file (UNIX)
        H_COMPRESS,             // Hcompressed FITS file
        ULDA_COMPRESS,          // ULDA compressed FITS file
        GZIP_COMPRESS           // GZIPed FITS file
    };


    Compress();

    int compress(int read_fd, int write_fd, CompressType type,
                 int compress_flag = 1);

    int decompress(int read_fd, int write_fd, CompressType type);

    int compress(const char* infile, const char* outfile, CompressType type,
                 int compress_flag = 1, int mmap_flag = 1);

    int decompress(const char* infile, const char* outfile, CompressType type,
                   int mmap_flag = 1);

    int compress(const char* file, CompressType type, int compress_flag = 1,
                 int mmap_flag = 1);

    int decompress(const char* file, CompressType type, int mmap_flag = 1);


    int compress(const char* inbuf, int inbufsz, char*& outbuf, int& outbufsz,
                       CompressType ctype, int compress_flag = 1);

    int decompress(const char* inbuf, int inbufsz, char*& outbuf, int& outbufsz,
                   CompressType ctype);

};

DESCRIPTION

 
This class is a C++ wrapper around the CADC "press" routines for FITS
image compression. The methods all do the same thing: compress or
decompress an image.  Some methods take file names as arguments,
others pointers to memory areas. The type of compression is specified
as an enum value "CompressType".

The methods called "compress" all take an optional flag argument that
indicates compression or decompression. The methods called
"decompress" are shortcut, inline methods that call compress with the
decompress flag on.

CONSTRUCTORS

 
Compress()
        Initialize the object.

METHODS

 
compress(read_fd, write_fd, type, compress_flag)
        Compress (or decompress), reading from the given read file
        descriptor and writing the results to the given write fd. If
        compress_flag is true, compress, otherwise decompress the
        file.

decompress(read_fd, write_fd, type)
        Decompress, reading from the given read file descriptor and
        writing the results to the given write fd.

compress(infile, outfile, type, compress_flag, mmap_flag)
        Compress (or decompress) the given input file and put the
        result in outfile.  If compress_flag is true, compress,
        otherwise decompress the file.  If mmap_flag is true, use mmap
        to map the file to memory.  Note: we can just open the file
        and use the fd, but the "press" C routines do unbuffered I/O
        on each char, which is slow. We can mmap the file to memory
        and use the "mem to mem" version to improve speed somewhat.

decompress(infile, outfile, type, mmap_flag)
        Decompress the given input file and put the result in outfile.

compress(file, type, compress_flag, mmap_flag)
        Compress (decompress) the file in place using the given
        compress type.  If compress_flag is true, compress, otherwise
        decompress the file.

decompress(file, type, mmap_flag)
        Decompress the file in place.

compress(inbuf, inbufsz, outbuf, outbufsz, ctype, compress_flag)
        Compress (or decompress) the contents of inbuf using the given
        compress type and allocate the results to outbuf.  inbufsz is
        the size of the input buffer.  outbufsz is an estimate of the
        outbuf size on input and the actual size on output.  If
        compress_flag is true, compress, otherwise decompress the
        file.  It is the caller's responsibility to free() the outbuf
        when no longer needed.

decompress(inbuf, inbufsz, outbuf, outbufsz, ctype)
        Decompress inbuf and allocate results in outbuf.

 


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Last change: 08 Sep 98