A.I.

Michał ‘mina86’ Nazarewicz | 22 września 2013

While cleaning Tiny Applications Collection a little I’ve dropped both artificial intelligence scripts. However, not wanting to let them disappear, I’ve decided to post them here for posterity.

The first one is an eight line of code version that might just be what Sid wrote as his first program ever:

#!/usr/bin/perl -wWtT
while (<>) {
	if (/[aeiouyAEIOUY][^a-zA-Z]*$/) {
		print "Yes.\n";
	} elsif (!/^\s*$/) {
		print "No.\n";
	}
}

The second one is an “improved” six-line version akin to Pitr’s code:

#!/usr/bin/perl -wWtTn
if (/[aeiouyAEIOUY][^a-zA-Z]*$/) {
	print "No!\n";
} elsif (!/^\s*$/) {
	print "Yes.\n";
}

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Standard-agnostic HTML code

Michał ‘mina86’ Nazarewicz | 17 lipca 2013

HTML has gone quite a long way since its inception. This means a lot of new features but also some small incompatibilities which may pose issues in certain situations. For instance, when posting a code snippet for others to include on their websites, it’s best if it works correctly on as many sites as possible which implies being compatible with as many versions of HTML as possible. But how to create a snippet that works both in HTML and XHTML? Here are a few tips:

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CSS sprites as background

Michał ‘mina86’ Nazarewicz | 6 maja 2013

CSS sprites aren’t anything new. They have been around for years now, and are one of the methods to optimise website load time. The idea is to incorporate several images into a single bigger one and in this way decrease number of round trips between HTTP server and a browser.

In its traditional use, CSS sprites work as a replacement for images and cannot be used as a background. But background is exactly how I’d implemented quote image left of long quotes and flags indicating language paragraph was written in, e.g.:

A few of the entries on my blog have text both in English and Polish. On those, I use some simple icons to indicate which is which:

Polish flag on the left indicates paragraph is written in Polish.

Union Jack on the left indicates paragraph is written in English.

After a bit of playing around I finally figured out how to get this working, and even though there are some caveats, sprites can be used as a top-left no-repeat background image as well.

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The fifth generation

Michał ‘mina86’ Nazarewicz | 29 marca 2013

This day must have come sooner or later. Even more so since I love squeezing every byte out of the data being sent over the network, which is why source of this website is so unreadable (don’t worry though, readable sources are available in a git repository).

So yeah. I’ve switched this website to HTML5 with some of it’s new elements and optional tags removed. After years of using XHTML 1.1 it feels a bit weird not closing tags, but I guess a few saved bytes are worth it, aren’t they? ;)

I’ve even got my electric slash working in Emacs’s html-mode (ie. if I press slash after < sign, inner most element is closed automatically).

Unfortunately, not all is so shiny. For some reason, automatic pagination on entries list page and “load content” link stopped working under Opera. The way those work is by making an XMLHttpRequest and injecting portion of the fetched document in appropriate place. For some reason, Opera ends up with a DOMException: INVALID_STATE_ERR.

SSL and dropping “www.” with mod_rewrite

Michał ‘mina86’ Nazarewicz | 10 lutego 2013

Surprisingly I couldn’t find any HTTPS-aware examples how to drop the www. prefix from web hosts in Apache, so I had to come up with one myself. Firstly, the following lines need to find their way to the end of Apache configuration file (/etc/httpd/conf/httpd.conf or something):

RewriteEngine on
RewriteCond %{HTTPS} off
RewriteCond %{HTTP_HOST} ^www\.(.*)$
RewriteRule ^(.*)$ http://%1$1 [L,R=301]

Secondly, analogous lines need to be added inside of the <VirtualHost _default_:443> directive of mod_ssl configuration file (/etc/httpd/conf.d/ssl.conf or similar), like so:

<VirtualHost _default_:443>
	# … various directives …

	# Here’s what needs to be added:
	RewriteEngine on
	RewriteCond %{HTTP_HOST} ^www\.(.*)$
	RewriteRule ^(.*)$ https://%1$1 [L,R=301]
</VirtualHost>

Now, after a restart, Apache will drop the www. prefix for both secure and insecure connections.

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CMA po polsku

Michał ‘mina86’ Nazarewicz | 22 stycznia 2013

Będę miał dzisiaj przyjemność prezentować Contiguous Memory Allocator na seminarium dyplomowym (CMA jest bowiem tematem mojej pracy). Dostępny jest również referat opisujący z większą ilością detali zawartość slajdów. Aktualizacja: Z racji, że jestem już po obronie, dodaję również link do pracy inżynierskiej.

Prezentacja nie opisuje sposobu użycia CMA zatem po więcej szczegółów odsyłam do materiałów z LCE 2012. No i oczywiście jest również strona mina86.com/cma/, z której linkuję do przeróżnych materiałów dotyczących CMA.

CMA on LCE/ELCE 2012

Michał ‘mina86’ Nazarewicz | 7 listopada 2012

LinuxCon / Embedded Linux Conference Europe 2012 is nearly over, and I had a pleasure of talking about the Contiguous Memory Allocator. The slides from the talk are embedded below, are available for download from Google Drive, and their source code can be accessed at GitHub.

Unfortunately, in contrast to other LCE/ELCE conferences, talks were not recorded, so the video of the presentation is not available.

For more links regarding CMA, I have set up a resource page at mina86.com/cma/. Beside the link to the final CMA patchset and to the LCE/ELCE presentation, it links to various articles and patches relating to CMA directly or indirectly.

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LazyProxy in Python

Michał ‘mina86’ Nazarewicz | 8 lipca 2012

Paths of destiny lead mysterious ways. Not so long ago, I was a hard-core C hacker and now, I spend a lot of the time coding in Python.

In somehow related news, I have discovered that my search-foo is not good enough, when I was unable to find a decent implementations of several design patterns in Python.

What I needed was a generic proxy that would defer initialisation of an object to the moment it is first used. Here is what I came up with:

class LazyProxy(object):
    __slots__ = '__get'

    def __init__(self, cls, *args, **kw):
        object.__setattr__(self, '_LazyProxy__get',
                           lambda: self.__set(cls(*args, **kw)))

    def __set(self, obj):
        object.__setattr__(self, '_LazyProxy__get', lambda: obj)
        return obj

    def __getattr__(self, name):
        return getattr(self.__get(), name)

    def __setattr__(self, name, value):
        return setattr(self.__get(), name, value)

    def __delattr__(self, name):
        return delattr(self.__get(), name)

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Deep Dive into Contiguous Memory Allocator

Michał ‘mina86’ Nazarewicz | 10 czerwca 2012

This is the first part of an extended version of an LWN article on CMA. It contains much more detail on how to use CMA, and a lot of boring code samples. Should you be more interested in an overview, consider reading the original instead.

Contiguous Memory Allocator (or CMA) has been developed to allow big physically contiguous memory allocations. By initialising early at boot time and with some fairly intrusive changes to Linux memory management, it is able to allocate big memory chunks without a need to grab memory for exclusive use.

Simple in principle, it grew to be a quite complicated system which requires coöperation between boot-time allocator, buddy system, DMA subsystem, and some architecture-specific code. Still, all that complexity is usually hidden away and normal users won’t be exposed to it. Depending on perspective, CMA appears slightly different and there are different things to be done and look for.

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Null: The never-ending story

Michał ‘mina86’ Nazarewicz | 27 marca 2011

I have already mentioned some problems with the null pointer but my recent discovery knocked my socks off.

By now, it should come with no surprise to anyone that 0 in pointer context acts as a null pointer (no matter of its actual representation). Moreover, it takes only a tiny bit of experimenting to figure out that expressions like (int)0 do as well. The latter is in itself a bit of a pita but it is conforming to the C++ standard which says:

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