1FastRaw(3) User Contributed Perl Documentation FastRaw(3)
2
6 PDL::IO::FastRaw -- A simple, fast and convenient io format for PerlDL.
7
9 use PDL;
10 use PDL::IO::FastRaw;
11 writefraw($pdl,"fname"); # write a raw file
13 $pdl2 = readfraw("fname"); # read a raw file
15 $pdl2 = PDL->readfraw("fname");
16 $pdl3 = mapfraw("fname2",{ReadOnly => 1}); # mmap a file, don't read yet
18 $pdl4 = maptextfraw("fname3",{...}); # map a text file into a 1-D pdl.
20
22 This is a very simple and fast io format for PerlDL. The disk data
23 consists of two files, a header metadata file in ASCII and a binary
24 file consisting simply of consecutive bytes, shorts or whatever.
25 It is hoped that this will not only make for a simple PerlDL module for
27 saving and retrieving these files but also make it easy for other pro‐
28 grams to use these files.
29 The format of the ASCII header is simply
31 <typeid>
33 <ndims>
34 <dim0> <dim1> ...
35 The binary files are in general NOT interchangeable between different
37 architectures since the binary file is simply dumped from the memory
38 region of the piddle. This is what makes the approach efficient.
39 It is also possible to mmap the file which can give a large speedup in
41 certain situations as well as save a lot of memory by using a disk file
42 as virtual memory. When a file is mapped, parts of it are read only as
43 they are accessed in the memory (or as the kernel decides: if you are
44 reading the pages in order, it may well preread some for you).
45 Note that memory savings and copy-on-write are operating-system depen‐
47 dent - see Core.xs and your operating system documentation for exact
48 semantics of whatever. Basically, if you write to a mmapped file with‐
49 out "ReadOnly", the change will be reflected in the file immediately.
50 "ReadOnly" doesn't really make it impossible to write to the piddle but
51 maps the memory privately so the file will not be changed when you
52 change the piddle. Be aware though that mmapping a 40Mb file without
53 "ReadOnly" spends no virtual memory but with "ReadOnly" it does reserve
54 40Mb.
55
57 readfraw
58 Read a raw format binary file
60 $pdl2 = readfraw("fname");
62 $pdl2 = PDL->readfraw("fname");
63 writefraw
65 Write a raw format binary file
67 writefraw($pdl,"fname");
69 mapfraw
71 Memory map a raw format binary file (see the module docs also)
73 $pdl3 = mapfraw("fname2",{ReadOnly => 1});
75 The "mapfraw" command supports the following options (not all combina‐
77 tions make sense):
78 Dims, Datatype
80 If creating a new file or if you want to specify your own
81 header data for the file, you can give an array reference and a
82 scalar, respectively.
83 Creat Create the file. Also writes out a header for the file.
85 Trunc Set the file size. Automatically enabled with "Creat". NOTE:
87 This also clears the file to all zeroes.
88 ReadOnly
90 Disallow writing to the file.
91 maptextfraw
93 Memory map a text file (see the module docs also).
95 Note that this function maps the raw format so if you are using an
97 operating system which does strange things to e.g. line delimiters
98 upon reading a text file, you get the raw (binary) representation.
99 The file doesn't really need to be text but it is just mapped as one
101 large binary chunk.
102 This function is just a convenience wrapper which firsts "stat"s the
104 file and sets the dimensions and datatype.
105 $pdl4 = maptextfraw("fname", {options}
107 The options other than Dims, Datatype of "mapfraw" are supported.
109
111 Should be documented better. "writefraw" and "readfraw" should also
112 have options (the author nowadays only uses "mapfraw" ;)
113
115 Copyright (C) Tuomas J. Lukka 1997. All rights reserved. There is no
116 warranty. You are allowed to redistribute this software / documentation
117 under certain conditions. For details, see the file COPYING in the PDL
118 distribution. If this file is separated from the PDL distribution, the
119 copyright notice should be included in the file.
120perl v5.8.8 2000-03-14 FastRaw(3)