http://www.shlomifish.org/me/blogs/ http://shlomif-tech.livejournal.com/72971.html <p> If you are using <a href="http://en.wikipedia.org/wiki/Travis_CI" rel="nofollow">Travis CI</a>, you can check the latest build after a failed build by going to the “Build History” tab in your project’s main page (= https://travis-ci.org/shlomif/fc-solve or equivalent), and selecting the new commit. </p> <h2>Licence</h2> <p> Copyright by Shlomi Fish, 2016. </p> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> on how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux tip tech open-source tech tip foss http://shlomif-tech.livejournal.com/72971.html http://shlomif-tech.livejournal.com/72971.html Fri, 27 May 2016 12:43:21 GMT http://fc-solve.blogspot.com/2016/03/freecell-solver-420-was-released.html <p> <a href="http://fc-solve.shlomifish.org/">Freecell Solver</a> version 4.2.0, has been released. It is available in the form of a source archive, from <a href="http://fc-solve.shlomifish.org/download.html">the download page</a>. Freecell Solver is an open source library and some command line applications, for automatically solving several variants of card Solitaire / Patience games, including Freecell. </p> <p> This release sports the new configuration theme “-l conspiracy-theory” (or “-l ct”) which is somewhat faster than the best contender up to it, “-l amateur-star”, some relatively minor bug fixes, new compile-time options, and many small and somewhat larger code cleanups, refactorings, and optimisations. </p> <p> “conspiracy-theory” is a reference to the Jewish holiday of <a href="https://en.wikipedia.org/wiki/Purim">Purim</a>, which took place around the time of its release and an <a href="http://shlomif.livejournal.com/62243.html">old post</a> of mine about it. </p> <p> Enjoy! </p> Shlomi Fish ( shlomif@shlomifish.org ) freecell open source release solitaire solver solving tag:blogger.com,1999:blog-96099636168698788.post-3011534562121233530 Fri, 25 Mar 2016 16:14:00 +0000 2016-03-25T09:14:51.183-07:00 http://shlomif.livejournal.com/68825.html <p> In order to sync the clock using <a href="http://en.wikipedia.org/wiki/Network_Time_Protocol" rel="nofollow">NTP</a>, the network time protocol so your computer clock won't be skewed, one should run the following command as root: “<code>ntpd -q -g -x</code>”. This has been a constant problem for me in part because SSL/HTTPS sites may not work if your clock is out-of-date. </p> <p> You can find the meaning of the individual flags in the <a href="http://linux.die.net/man/8/ntpd" rel="nofollow">ntpd man page</a>. </p> <p> Cheers and happy upcoming <a href="http://en.wikipedia.org/wiki/Purim" rel="nofollow">Purim</a> in case you celebrate. </p> <h2>Licence</h2> <p> Copyright by Shlomi Fish, 2015. </p> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> on how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) foss linux tip tech http://shlomif.livejournal.com/68825.html http://shlomif.livejournal.com/68825.html Thu, 10 Mar 2016 20:03:32 GMT http://shlomif-tech.livejournal.com/72917.html <h2>2015-12-03: Tech Tip: Speed up building perl 5 by not installing the man pages</h2> <p> When building <a href="http://dev.perl.org/perl5/source.html" rel="nofollow">perl 5 from source</a>, one can speed up the "make" and "make install" stages significantly by not installing the man pages. To do so, pass the options “-Dman1dir=none -Dman3dir=none” to “sh Configure”. </p> <p> Cheers, and happy upcoming <a href="https://en.wikipedia.org/wiki/Hanukkah" rel="nofollow">Chanukkah</a>, and happy Christmas and/or Yulth or whatever winter holiday you celebrate. </p> <h2>Call for action</h2> <p> Creative Commons has set up <a href="http://creativecommons.org/campaigns/stop-the-tpp" rel="nofollow">a campaign</a> to stop <a href="http://creativecommons.org/weblog/entry/46455" rel="nofollow">TPP - the Trans-Pacific Partnership</a>. Please consider signing it and spreading the word. </p> <h2>Licence</h2> <p> Copyright by Shlomi Fish, 2015. </p> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> on how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux tip perl tech open-source tech tip foss http://shlomif-tech.livejournal.com/72917.html http://shlomif-tech.livejournal.com/72917.html Thu, 03 Dec 2015 16:37:51 GMT http://shlomif-tech.livejournal.com/72545.html <p> When pressing «Ctrl+B;"» in <a href="https://en.wikipedia.org/wiki/Tmux" rel="nofollow">tmux</a> to split a pane vertically there, one will notice that tmux splits the existing pane into two which can result in smaller and smaller panes. In order to fix this, one can type «Ctrl+B;M-2» (where “M” is the <a href="https://en.wikipedia.org/wiki/Meta_key" rel="nofollow">Meta key</a> and is normally “Alt” on most keyboards.) which will make all the panes equally heighted. </p> <p> I found this feature after wondering whether it existed, and then searching for it in the tmux man page. </p> <h2>Licence</h2> <p> Copyright by Shlomi Fish, 2015. </p> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> on how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux tip tech open-source tech tip foss http://shlomif-tech.livejournal.com/72545.html http://shlomif-tech.livejournal.com/72545.html Fri, 06 Nov 2015 10:19:27 GMT http://fc-solve.blogspot.com/2015/09/freecell-solver-400-was-released.html <p> <a href="http://fc-solve.shlomifish.org/">Freecell Solver</a> version 4.0.0, has been released. It is available in the form of a source archive, from <a href="http://fc-solve.shlomifish.org/download.html">the download page</a>. Freecell Solver is an open source library and some command line applications, for automatically solving several variants of card Solitaire / Patience games, including Freecell. </p> <p> This release sports the integration of the scans of Tom Holroyd’s patsolve for improved atomic moves-based solving, some other new flags with bug fixes, a transition of the Python code to Python 3, and some other changes that are mentioned in <a href="http://fc-solve.shlomifish.org/docs/distro/NEWS.html">the NEWS file</a>. </p> <p> The most significant digit was increased due to the integration of patsolve. Enjoy! </p> Shlomi Fish ( shlomif@shlomifish.org ) freecell open source release solitaire solver solving tag:blogger.com,1999:blog-96099636168698788.post-4449217081539455140 Mon, 28 Sep 2015 14:51:00 +0000 2016-03-11T09:10:58.814-08:00 http://shlomif-tech.livejournal.com/72415.html <p> A constant annoyance when trying to use the Firefox extension “<a href="http://barisderin.com/?p=120" rel="nofollow">Personas Rotator</a>” was that downloading the favourites file from the Firefox addons site failed, which made it stop rotating. I recently found a solution for that which I'd like to share. </p> <p> First of all, login to <a href="https://addons.mozilla.org/en-US/firefox/themes/" rel="nofollow">the Mozilla addons site</a> and access and bookmark <a href="https://addons.mozilla.org/en-US/firefox/collections/mine/favorites/format%3Ajson?src=" rel="nofollow">the JSON data file’s URL</a>. Save it to a file and host it using a local HTTP service (such as Apache, <a href="http://www.garyrobinson.net/2004/03/one_line_python.html" rel="nofollow">the one line Python HTTP service</a> command line, or <a href="http://opensource.dyc.edu/sthttpd" rel="nofollow">sthttpd</a>’s “thttpd -p $PORT” invocation). </p> <p> Then, go to Firefox’s “about:config”, access the “extensions.personas.favorites-feed.url” key and change it to the locally served one. It should work fine after restarting Firefox, and one upside to it would be that you no longer need to be logged in to addons.mozilla.org for it to work. </p> <p> Remember to save the file again every once-in-a-while, after you have added new favourites. A final note is that a “file://” URL may work fine as well, but I have not tried it yet. </p> <p> Happy rotating, and <a href="http://en.wikipedia.org/wiki/Rosh_Hashanah" rel="nofollow">Shanah Tovah</a> if appropriate! </p> <h2>Licence</h2> <p> Copyright by Shlomi Fish, 2015. </p> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> on how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux firefox tip tech mozilla open-source tech tip foss http://shlomif-tech.livejournal.com/72415.html http://shlomif-tech.livejournal.com/72415.html Tue, 15 Sep 2015 12:18:06 GMT http://shlomif-hsite.livejournal.com/19649.html <p> Here are the recent updates for <a href="http://www.shlomifish.org/" rel="nofollow">Shlomi Fish’s Homepage</a>. </p> <ol> <li> <p> A new bit <a href="http://www.shlomifish.org/humour/bits/HTML-6/" rel="nofollow">“Announcing ‘HTML 6’, the New Version of the Web”</a> was published on 1 April 2015: </p> <blockquote> <p> <b>1 April, 2015, Tel Aviv, Israel:</b> Today, the World Wide Web Consortium (W3C) announced the immediate availability of the new version of the web — <b>HTML 6</b> — pronounced “HTML Sicks [sic]” with the motto “HTML 6 is sick!”. “We concluded that the previous version of the World Wide Web’s standards suite, HTML5, has exceeded its flexibility and usability, and we need to start over”, said Tim Berners-Lee, the director of the W3C. </p> </blockquote> </li> <li> <p> There’s a new <a href="http://www.shlomifish.org/philosophy/computers/web/models-for-commerce/" rel="nofollow">list of “Alternative” commercial models</a> for Web-based commerce that do not involve intrusive advertising. </p> </li> <li> <p> There’s a new <a href="http://www.shlomifish.org/open-source/resources/graphics-programs/" rel="nofollow">list of graphics software applications</a>. </p> </li> <li> <p> We now mirror <a href="http://www.shlomifish.org/humour/by-others/funroll-loops/" rel="nofollow">funroll-loops.info (“Gentoo is Rice”)</a>, and the old feature <a href="http://www.shlomifish.org/humour/by-others/how-to-make-square-corners-with-CSS/" rel="nofollow">“How to Make Square Corners with CSS”</a>, which disappeared from the Web. </p> </li> <li> <p> There are new factoids in <a href="http://www.shlomifish.org/humour/bits/facts/" rel="nofollow">the collections of factoids about people and thing</a>: </p> <blockquote> <p> A rose by a name picked by Chuck Norris, will smell sweeter. </p> <p> The reason the Messiah has not come yet, is because Chuck Norris keeps finding faults in God’s plan for his coming. </p> </blockquote> </li> <li> <p> There are <a href="http://www.shlomifish.org/humour.html#dizzying_intellect" rel="nofollow">new quotes</a> in the collection of Aphorisms: </p> <blockquote> <p> Some people grow older and wiser. Not I. I grow older and more foolish. </p> </blockquote> </li> </ol> <p> Hope you enjoy all that, and if you’re Jewish, I hope you enjoy the upcoming <a href="http://en.wikipedia.org/wiki/Rosh_Hashanah" rel="nofollow">Rosh Hashanah</a> and the rest of the Jewish Autumn holidays. </p> Shlomi Fish ( shlomif@shlomifish.org ) quotes facts html5 chuck norris open humor html 5 humour http://shlomif-hsite.livejournal.com/19649.html http://shlomif-hsite.livejournal.com/19649.html Thu, 03 Sep 2015 18:49:52 GMT http://shlomif-tech.livejournal.com/72038.html <p> In order to build <a href="http://en.wikipedia.org/wiki/GNU_Guile" rel="nofollow">GNU Guile</a> (or at least its version 2.x), it is important not to pass the “-j$N” flag to “make”. Without the flag, the compilation will be faster (counterintuitively I admit), because some of the build tasks spawn as many processes or threads as the CPU cores on the machine, and with the flag, they get congested and the build is slower. Cheers! </p> <h2>Licence</h2> <p> Copyright by Shlomi Fish, 2015. </p> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> of how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux tip speed tech open-source tech tip foss http://shlomif-tech.livejournal.com/72038.html http://shlomif-tech.livejournal.com/72038.html Tue, 01 Sep 2015 15:22:55 GMT http://shlomif-tech.livejournal.com/71746.html <p> <a href="https://metacpan.org/pod/distribution/CPAN-Mini/bin/minicpan" rel="nofollow">minicpan</a> is a tool to create or update a minimal local mirror of CPAN (= the “Comprehensive Perl Archive Network”), that contains only the latest releases of CPAN distributions. Now, one problem I ran into when using it is that “minicpan” did not seem to delete the older downloaded releases after they were superseded by newer ones. A few days ago I found a solution to this problem. </p> <p> What you can do is: </p> <ol> <li> <p> Move away the minicpan’s mirror’s top directory (<b>do not delete it!</b>) </p> </li> <li> <p> Set up a localhost HTTP service on a high TCP port which will serve the moved minicpan directory. For that you can use <a href="http://www.garyrobinson.net/2004/03/one_line_python.html" rel="nofollow">the one line Python HTTP service</a> command line or <a href="http://opensource.dyc.edu/sthttpd" rel="nofollow">shttpd</a>’s “thttpd -p $PORT” invocation or whatever. </p> </li> <li> <p> Run the “minicpan” command while pointing the remote to the localhost mirror of the old minicpan mirror, using the “-r” flag or by temporarily editing the “~/.minicpanrc” file. </p> </li> </ol> <p> Voila! Now the mirror will only contain the latest releases, and you can remove the old, moved-away, minicpan directory, and cancel the HTTP service. </p> <h2>Licence</h2> <p> Copyright by Shlomi Fish, 2015. </p> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> of how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux tip perl tech open-source tech tip cpan foss http://shlomif-tech.livejournal.com/71746.html http://shlomif-tech.livejournal.com/71746.html Mon, 20 Jul 2015 10:54:09 GMT http://shlomif-tech.livejournal.com/71570.html <p> Let’s suppose you are packaging a software application using <a href="https://en.wikipedia.org/wiki/RPM_Package_Manager" rel="nofollow">RPM</a> or a similar packaging system, and this application contains some automated tests that can be run using “make test”, “make check” or similar. You may opt to put them inside a “%check” section, but the problem now is that they may fail. </p> <p> The solution I used in this case (assuming fixing the tests was out of scope of my work as a packager) was to comment out the command that ran the tests, but this is not ideal because that way the tests will also be disabled in subsequent versions of the application, unless the packager remembers to reenable them. </p> <p> Recently, I discovered a better way to do that, after inspecting the source of a <a href="http://www.mageia.org/en/" rel="nofollow">Mageia Linux</a> package. One needs do something like that: </p> <pre> %define known_to_fail_version 1.82 %check if test "%{version}" = "%{known_to_fail_version}" ; then true else # Run the tests. make check fi </pre> <p> This way, the tests will get run again for subsequent versions of the packaged application, and if they fail again one can set “known_to_fail_version” to a new value. </p> <p> I hope you also find it a cool trick. Cheers! </p> <h2>Licence</h2> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> of how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux tip tech open-source rpm tech tip foss http://shlomif-tech.livejournal.com/71570.html http://shlomif-tech.livejournal.com/71570.html Tue, 14 Jul 2015 08:53:24 GMT http://shlomif-tech.livejournal.com/71385.html <p> In order to debug Mozilla Firefox’s User Interface code (so-called “chrome” code), you should toggle the “Enable chrome and add-on debugging” checkbox in the Developer Toolbar’s setting and then go to “Tools → Web Developer → Browser Toolbox”. Thanks to jdm on irc.mozilla.org for part of this tip. Cheers and happy <a href="http://en.wikipedia.org/wiki/Independence_Day_%28United_States%29" rel="nofollow">United Stated Independence Day</a> (4th of July) in case you are an American. </p> <h2>Licence</h2> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> of how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux firefox tip tech open-source debugging tech tip foss http://shlomif-tech.livejournal.com/71385.html http://shlomif-tech.livejournal.com/71385.html Fri, 03 Jul 2015 08:39:31 GMT http://shlomif-tech.livejournal.com/71047.html <p> I noticed that one can often fix poor home Internet connectivity (I have an <a href="https://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_line" rel="nofollow">ADSL connection</a> but it may apply to other types of Internet connection), by powering off the router and starting it again (“restart/reboot”). So I’ve made a mental note to keep it in mind and now it’s in this blog as a tip. Cheers! </p> <h2>Licence</h2> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> of how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux tip tech open-source tech tip foss http://shlomif-tech.livejournal.com/71047.html http://shlomif-tech.livejournal.com/71047.html Thu, 25 Jun 2015 09:48:32 GMT http://shlomif-tech.livejournal.com/70747.html <p> “git” is an open-source distributed version control system that has recently gained a lot of popularity. The “git bisect start” synopsis in “git help bisect” is somewhat misleading: </p> <pre> git bisect start [--no-checkout] [&lt;bad&gt; [&lt;good&gt;...]] [--] [&lt;paths&gt;...] </pre> <p> One has to specify both the “bad” and the “good” revisions explicitly or else “git bisect” will wait for the missing ones to be specified, which will be confusing. So specify them immediately at the “git bisect start” invocation. </p> <p> Incidentally, <a href="http://www.nntp.perl.org/group/perl.perl5.porters/2015/06/msg228300.html" rel="nofollow">perl-5.22.0</a> was released a few days ago. Grab it while it’s hot! </p> <h2>Licence</h2> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> of how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux tip tech open-source tech tip foss http://shlomif-tech.livejournal.com/70747.html http://shlomif-tech.livejournal.com/70747.html Sat, 06 Jun 2015 17:11:00 GMT http://shlomif-tech.livejournal.com/70518.html <p> Here's a tip you may find useful about how to determine which program is emitting sounds on a modern <a href="http://en.wikipedia.org/wiki/Linux" rel="nofollow">Linux</a> system. This tip requires <a href="http://en.wikipedia.org/wiki/PulseAudio" rel="nofollow">PulseAudio</a> to be enabled , and if that's the case, just start up <a href="http://www.kde.org/applications/multimedia/kmix/" rel="nofollow">KDE’s KMix</a> and see which applications spring up in the “Playback Streams” tab. Hope it helps, and good luck. </p> <h2>Licence</h2> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version of it. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> of how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux tip tech tech tip http://shlomif-tech.livejournal.com/70518.html http://shlomif-tech.livejournal.com/70518.html Tue, 02 Jun 2015 15:02:25 GMT http://shlomif-tech.livejournal.com/70256.html <p> In the <a href="http://www.vim.org/" rel="nofollow">Vim</a> and GVim text editors, one can use <code>Ctrl+W;t</code> (or <tt>Ctrl+w;Ctrl+t</tt>) to go to the topmost/most top window (= a section of the screen in Vim terminology) and <code>Ctrl+W;b</code> to go to the bottommost/most bottom one. </p> <p> Cheers! </p> Shlomi Fish ( shlomif@shlomifish.org ) tip vim tip tech vim tech tip http://shlomif-tech.livejournal.com/70256.html http://shlomif-tech.livejournal.com/70256.html Fri, 29 May 2015 17:08:46 GMT http://shlomif-tech.livejournal.com/69991.html <p> Recently, I noticed that when running the VLC-2.2.0 prerelease, which is based on Qt 5 for its GUI, on my <a href="http://www.mageia.org/en/" rel="nofollow">Mageia</a> Linux 5 system on top of KDE 4, then in the playlist a single-click immediately played a file instead of selecting it, while reserving a double click for activation. After a long amount of research and thought, I figured out a way to configure Qt 5 on top of KDE. </p> <p> To do so: </p> <ol> <li> <p> Install lxqt-config and the “lxqt-qtplugin”. </p> </li> <li> <p> Add the line “<code>export QT_QPA_PLATFORMTHEME=lxqt</code>” somewhere before the desktop startup in your “.Xclients” or “.xinitrc” file (or in your “.bashrc”). </p> </li> <li> <p> Restart the X/KDE environment. </p> </li> <li> <p> Run “lxqt-config” to configure the appropriate behaviour. </p> </li> </ol> <p> This way one can use the Qt5 customisations of lxqt in KDE 4. Enjoy! </p> <h2>Licence</h2> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> of how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux tip tech tech tip kde http://shlomif-tech.livejournal.com/69991.html http://shlomif-tech.livejournal.com/69991.html Sat, 28 Feb 2015 12:12:47 GMT http://shlomif-tech.livejournal.com/69835.html <p> The book <a href="http://www.amazon.com/Fortune-Failure-Missed-Opportunities-Discoveries/dp/0631160876/ref=sr_1_2?ie=UTF8&amp;qid=1424966727&amp;sr=8-2&amp;keywords=fortune+or+failure" rel="nofollow"><i>Fortune or Failure: Missed Opportunities and Chance Discoveries</i></a> (which my family used to own, but which I did not read) gives the case to the important role of luck and chance in scientific discoveries. Recently, when working on <a href="https://projecteuler.net/problem=146" rel="nofollow">Project Euler Problem No. 146</a> I came up with a case of an accidental bug, that in turn led to an idea for a significant optimisation. </p> <p> The C code with the bug (which was in turn translated from some Perl code) looked something like that: </p> <pre> #define DIV 9699690 #define NUM_MODS 24024 #define NUM_PRIMES 8497392 int primes[NUM_PRIMES]; int mods[NUM_MODS]; typedef long long LL; static inline bool is_prime(LL n) { LL lim = (LL)(sqrt(n)); for (int p_idx=0; p_idx &lt; NUM_MODS ; p_idx++) { typeof (primes[p_idx]) p = primes[p_idx]; if (p &gt; lim) { return true; } if (n % p == 0) { return false; } } return true; } . . . for (int y_idx=0;y_idx&lt;sizeof(y_off)/sizeof(y_off[0]);y_idx++) { if (! is_prime(sq + y_off[y_idx])) { goto fail; } } for (int n_idx=0;n_idx&lt;sizeof(n_off)/sizeof(n_off[0]);n_idx++) { if (is_prime(sq + n_off[n_idx])) { goto fail; } } </pre> <p> As you can notice eventually, the problem was that in the <code>p_idx</code> loop, <code>NUM_MODS</code> should have been the larger <code>NUM_PRIMES</code>. This caused the test for primality to finish faster, but to sometimes return true instead of false. As a result, I noticed that some numbers were erroneously reported as suitable, but the program finished much faster. </p> <p> I corrected it and reran the program which was now much slower, but this led me to think that maybe the lower limit to the count of primes can be a pre-filter for primality for the “y_idx”/“y_off” numbers, that will run quicker and eliminate some numbers. As a result, I did this: </p> <pre> #define NUM_PRIMES__PRE_FILTER 24024 static inline bool is_prime__pre_filter(LL n) { LL lim = (LL)(sqrt(n)); for (int p_idx=0; p_idx &lt; NUM_PRIMES__PRE_FILTER ; p_idx++) { typeof (primes[p_idx]) p = primes[p_idx]; if (p &gt; lim) { return true; } if (n % p == 0) { return false; } } return true; } . . . for (int y_idx=0;y_idx&lt;sizeof(y_off)/sizeof(y_off[0]);y_idx++) { if (! is_prime__pre_filter(sq + y_off[y_idx])) { goto fail; } } for (int y_idx=0;y_idx&lt;sizeof(y_off)/sizeof(y_off[0]);y_idx++) { if (! is_prime(sq + y_off[y_idx])) { goto fail; } } for (int n_idx=0;n_idx&lt;sizeof(n_off)/sizeof(n_off[0]);n_idx++) { if (is_prime(sq + n_off[n_idx])) { goto fail; } } </pre> <p> This made the program finish in under a minute, while yielding the correct solution. The original program, with the bug fix, was still running after several minutes. </p> <p> So the bug proved to be useful and insightful. One possible future direction is to merge the two “y_idx” loops into a single function that will accept an array of numbers, and will check them all for primality using the same divisors simultaneously, so as soon as one of them is found to be non-prime, a verdict will be reached. </p> <h2>Licence</h2> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by-nc/3.0/" rel="nofollow">the Creative Commons Attribution Noncommercial 3.0 Unported</a> licence, or at your option any later version. See the <a href="http://www.shlomifish.org/meta/copyrights/" rel="nofollow">instructions</a> of how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux bug optimize http://shlomif-tech.livejournal.com/69835.html http://shlomif-tech.livejournal.com/69835.html Thu, 26 Feb 2015 18:23:14 GMT http://shlomif-tech.livejournal.com/69529.html <p> This will come as a surprise to few, but performing a separate <a href="https://en.wikipedia.org/wiki/Fork_%28system_call%29" rel="nofollow">fork()</a> and <a href="https://en.wikipedia.org/wiki/Exec_%28computing%29" rel="nofollow">EXECVE</a> system calls (e.g: for <code>`factor "$n"`</code> in Perl or <code>popen</code> in C), on each iteration of a loop can really kill performance. One option to reduce that would be to read individual lines from a <code>seq 2 999999 | xargs factor</code> loop, or avoid forking altogether. </p> <p> I discovered this issue while working on <a href="https://projecteuler.net/problem=141" rel="nofollow">Project Euler problem #141</a>, and I should have realised that the sub-100% CPU utilisation of the program was caused by the excessive spawning of new processes. </p> <h2>Licence</h2> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> of how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux tip optimize tech tech tip http://shlomif-tech.livejournal.com/69529.html http://shlomif-tech.livejournal.com/69529.html Sun, 22 Feb 2015 13:33:16 GMT http://shlomif-tech.livejournal.com/69336.html <p> If you’re having a problem playing <a href="https://en.wikipedia.org/wiki/Jamendo" rel="nofollow">Jamendo</a> tracks after pressing the “Listen” button (such as on <a href="https://www.jamendo.com/en/list/a132792/nanofly" rel="nofollow">this page</a>) on Firefox running on Linux, then try to install the packages «gstreamer0.10-plugins-bad gstreamer0.10-plugins-good gstreamer0.10-plugins-ugly gstreamer0.10-mpeg gstreamer0.10-ffmpeg» (relevant to Mageia; try their equivalent in other distributions), restart Firefox and try again. The problem is that Firefox needs extra gstreamer plugins to play proprietary formats in <a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Supported_media_formats" rel="nofollow">HTML audio and video elements</a>. Cheers! </p> <p> (Thanks to “dolske” from #firefox on irc.mozilla.org for their help.) </p> <h2>Licence</h2> <p> You can reuse this entry under <a href="http://creativecommons.org/licenses/by/3.0/" rel="nofollow">the Creative Commons Attribution 3.0 Unported</a> licence, or at your option any later version. See the <a href="http://www.shlomifish.org/meta/copyrights/#cc_by_intr" rel="nofollow">instructions</a> of how to comply with it. </p> Shlomi Fish ( shlomif@shlomifish.org ) linux firefox tip tech tech tip http://shlomif-tech.livejournal.com/69336.html http://shlomif-tech.livejournal.com/69336.html Thu, 05 Feb 2015 08:34:51 GMT