[Octave-patch-tracker] [patch #7748] Improved speed for textscan & textread for format repeat count

[Philip Nienhuis]

URL:
  <http://savannah.gnu.org/patch/?7748>

                 Summary: Improved speed for textscan & textread for format
repeat count
                 Project: GNU Octave
            Submitted by: philipnienhuis
            Submitted on: Wed 21 Mar 2012 12:09:31 AM CET
                Category: None
                Priority: 5 - Normal
                  Status: None
                 Privacy: Public
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any

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Details:

Inspired by this thread:

https://mailman.cae.wisc.edu/pipermail/help-octave/2012-March/050944.html

I have replaced some naive and extremely slow code in textread.m & textscan.m
and replaced it by block reading code. While there I also made some
improvement elsewhere.
Results on a Core Duo 2.5 GHz (WinXP):


octave-3.6.1.exe:1> dlmwrite ('test.csv', rand (16390, 4), ' ');

# Old textread:
octave-3.6.1.exe:2> tic; [a, b, c, d] = textread ('test.csv', "%f %f %f %f",
16384); toc
Elapsed time is 244.719 seconds.
octave-3.6.1.exe:3>

# New textread
octave-3.6.1.exe:1> tic; [a, b, c, d] = textread ('test.csv', "%f %f %f %f",
16384); toc
Elapsed time is 3.422 seconds.
octave-3.6.1.exe:2> test textread
PASSES 6 out of 6 tests
octave-3.6.1.exe:3>

# Old textscan:
octave-3.6.1.exe:1> fid = fopen ('test.csv');
octave-3.6.1.exe:2> tic; C = textscan (fid, "%f %f %f %f", 16384); toc
Elapsed time is 244.141 seconds.
octave-3.6.1.exe:3>

# New textscan:
octave-3.6.1.exe:1> fid = fopen ('test.csv');
octave-3.6.1.exe:2> tic; C = textscan (fid, "%f %f %f %f", 16384); toc
Elapsed time is 3.422 seconds.
octave-3.6.1.exe:3> test textscan
PASSES 13 out of 13 tests
octave-3.6.1.exe:4> fclose (fid);

# Just for comparison:
octave-3.6.1.exe:5> tic; C = dlmread ( 'test.csv', ' ', 'A1:D16384'); toc
Elapsed time is 0.2 seconds.
octave-3.6.1.exe:6> size (C)
ans =

   16384       4

octave-3.6.1.exe:7>


.... so a binary textscan would still be preferrable. 
Yet a 70+ times faster script version (for moderately sized files) isn't bad
either.

changeset attached, + the files themselves for those who can't wait nor
patch.

Enjoy




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File Attachments:


-------------------------------------------------------
Date: Wed 21 Mar 2012 12:09:31 AM CET  Name: textread_textscan.patch  Size:
13kB   By: philipnienhuis

<http://savannah.gnu.org/patch/download.php?file_id=25421>
-------------------------------------------------------
Date: Wed 21 Mar 2012 12:09:31 AM CET  Name: textread.m  Size: 6kB   By:
philipnienhuis

<http://savannah.gnu.org/patch/download.php?file_id=25422>
-------------------------------------------------------
Date: Wed 21 Mar 2012 12:09:31 AM CET  Name: textscan.m  Size: 13kB   By:
philipnienhuis

<http://savannah.gnu.org/patch/download.php?file_id=25423>

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