PDL::IO::FastRaw--3pm

FastRaw(3pm)          User Contributed Perl Documentation         FastRaw(3pm)



NAME
       PDL::IO::FastRaw -- A simple, fast and convenient io format for PerlDL.

SYNOPSIS
        use PDL;
        use PDL::IO::FastRaw;

        writefraw($pdl,"fname");         # write a raw file

        $pdl2 = readfraw("fname");       # read a raw file
        $pdl2 = PDL->readfraw("fname");

        $pdl3 = mapfraw("fname2",{ReadOnly => 1}); # mmap a file, don't read yet

        $pdl4 = maptextfraw("fname3",{...}); # map a text file into a 1-D pdl.

DESCRIPTION
       This is a very simple and fast io format for PerlDL.  The disk data
       consists of two files, a header metadata file in ASCII and a binary
       file consisting simply of consecutive bytes, shorts or whatever.

       It is hoped that this will not only make for a simple PerlDL module for
       saving and retrieving these files but also make it easy for other pro-
       grams to use these files.

       The format of the ASCII header is simply

               <typeid>
               <ndims>
               <dim0> <dim1> ...

       The binary files are in general NOT interchangeable between different
       architectures since the binary file is simply dumped from the memory
       region of the piddle.  This is what makes the approach efficient.

       It is also possible to mmap the file which can give a large speedup in
       certain situations as well as save a lot of memory by using a disk file
       as virtual memory. When a file is mapped, parts of it are read only as
       they are accessed in the memory (or as the kernel decides: if you are
       reading the pages in order, it may well preread some for you).

       Note that memory savings and copy-on-write are operating-system depen-
       dent - see Core.xs and your operating system documentation for exact
       semantics of whatever. Basically, if you write to a mmapped file with-
       out "ReadOnly", the change will be reflected in the file immediately.
       "ReadOnly" doesn't really make it impossible to write to the piddle but
       maps the memory privately so the file will not be changed when you
       change the piddle. Be aware though that mmapping a 40Mb file without
       "ReadOnly" spends no virtual memory but with "ReadOnly" it does reserve
       40Mb.

FUNCTIONS
       readfraw

       Read a raw format binary file

        $pdl2 = readfraw("fname");
        $pdl2 = PDL->readfraw("fname");

       writefraw

       Write a raw format binary file

        writefraw($pdl,"fname");

       mapfraw

       Memory map a raw format binary file (see the module docs also)

        $pdl3 = mapfraw("fname2",{ReadOnly => 1});

       The "mapfraw" command supports the following options (not all combina-
       tions make sense):

       Dims, Datatype
               If creating a new file or if you want to specify your own
               header data for the file, you can give an array reference and a
               scalar, respectively.

       Creat   Create the file. Also writes out a header for the file.

       Trunc   Set the file size. Automatically enabled with "Creat". NOTE:
               This also clears the file to all zeroes.

       ReadOnly
               Disallow writing to the file.

       maptextfraw

       Memory map a text file (see the module docs also).

       Note that this function maps the raw format so if you are using an
       operating system which does strange things to e.g.  line delimiters
       upon reading a text file, you get the raw (binary) representation.

       The file doesn't really need to be text but it is just mapped as one
       large binary chunk.

       This function is just a convenience wrapper which firsts "stat"s the
       file and sets the dimensions and datatype.

        $pdl4 = maptextfraw("fname", {options}

       The options other than Dims, Datatype of "mapfraw" are supported.

BUGS
       Should be documented better. "writefraw" and "readfraw" should also
       have options (the author nowadays only uses "mapfraw" ;)

AUTHOR
       Copyright (C) Tuomas J. Lukka 1997.  All rights reserved. There is no
       warranty. You are allowed to redistribute this software / documentation
       under certain conditions. For details, see the file COPYING in the PDL
       distribution. If this file is separated from the PDL distribution, the
       copyright notice should be included in the file.



perl v5.8.8                       2000-03-14                      FastRaw(3pm)