December 31, 2017

A year ends, a new year begins

2017 is ending. It’s been a rather uneventful year, I’d say. About 6 months ago I started working on my master’s thesis - it plays with adding linear types to Go - and I handed that in about 1.5 weeks ago. It’s not really complete, though - you cannot actually use it on a complete Go program. The source code is of course available on GitHub, it’s a bunch of Go code for the implementation and a bunch of Markdown and LaTex for the document. ... Read more

February 14, 2017

jak-linux.org moved / backing up

In the past two days, I moved my main web site jak-linux.org (and jak-software.de) from a very old contract at STRATO over to something else: The domains are registered with INWX and the hosting is handled by uberspace.de. Encryption is provided by Let’s Encrypt. I requested the domain transfer from STRATO on Monday at 16:23, received the auth codes at 20:10 and the .de domain was transferred completely on 20:36 (about 20 minutes if you count my overhead). ... Read more

September 25, 2016

Introducing TrieHash, a order-preserving minimal perfect hash function generator for C(++)

Abstract I introduce TrieHash an algorithm for constructing perfect hash functions from tries. The generated hash functions are pure C code, minimal, order-preserving and outperform existing alternatives. Together with the generated header files,they can also be used as a generic string to enumeration mapper (enums are created by the tool). Introduction APT (and dpkg) spend a lot of time in parsing various files, especially Packages files. APT currently uses a function called AlphaHash which hashes the last 8 bytes of a word in a case-insensitive manner to hash fields in those files (dpkg just compares strings in an array of structs). ... Read more

April 9, 2014

ThinkPad X230 UEFI broken by setting a setting

Today, I decided to set my X230 back to UEFI-only boot, after having changed that for a bios upgrade recently (to fix a resume bug). I then choose to save the settings and received several error messages telling me that the system ran out of resources (probably storage space for UEFI variables). I rebooted my machine, and saw no logo appearing. Just something like an underscore on a text console. The system appears to boot normally otherwise, and once the i915 module is loaded (and we’re switching away from UEFI’s Graphical Output Protocol [GOP]) the screen works correctly. ... Read more

September 7, 2013

Review: ThinkPad X230

This week, a few hours after Lenovo announced the X240, I bought an X230. Normally, the X230 model I bought comes with a Core i5-3320M CPU, 4GB RAM, 500GB HDD. My model was a special set including a second 4GB RAM stick and a 128 GB mSATA Plextor SSD. It came without Windows; and the ThinkVantage button is black instead of blue and has no label. I put a fresh installation of unstable on it and tweaked it to save more power when on battery (enabled RC6++, and enabled autosuspend and other powertop suggestions with a script in /etc/pm/power. ... Read more

August 11, 2012

Implicit preferences in OR dependencies

Debian packages commonly use or dependencies of the form “a | b” to mean that a or b should be installed, while preferring option a over b. In general, for resolving an or dependency, we will try all options from the left to the right, preferring the left-most option. We also prefer real packages over virtual ones. If one of the alternatives is already installed we use that. def solve_or(or): best_real = None best_virtual = None for dep in or: for target in dep: if target. ... Read more

May 31, 2012

Memory allocators

In the past days, I looked at various memory allocators in a quest to improve performance in my multi-threaded test cases of a reference counting language runtime / object allocator (a fun project). It turns out the glibc’s memory allocator is relatively slow, especially if you do loops that create one element and destroy one element at the same time (for example, map() on a list you no longer use after you passed it to map). ... Read more

April 22, 2012

Reference Counting and Tail Calls

One thing I thought about today is reference counting in combination with tail calls. Imagine a function like this: function f(x) { return g(x+1); } Now consider that x is a reference counted object and that x + 1 creates a new object. The call to g(x + 1) shall be in tail call position. In most reference counted languages, the reference to an argument is owned by the caller. ... Read more

April 2, 2012

Currying in the presence of mutable parameters

In the language introduced yesterday, mutable parameters play the important role of representing the side effects of actions in the type system and thus ensure referential transparency. One of the questions currently unaddressed is how to handle currying in the presence of mutable parameters. In order to visualise this problem, consider a function printLn(mutable IO, String line) If we bind the the first parameter, what should be the type of the function, and especially important how do we get back the mutable parameter? ... Read more

April 1, 2012

Functional programming language for Python programmers and friends

Just for you, and this time in the Pythonesque rendering. module main: import std (range) import std.io (printf, IO) # print the Fahrenheit-Celcius table for fahr = 0, 20, ..., 300 function main(mutable IO io): Int lower = 0 # lower bound Int upper = 300 # upper bound Int step = 20 # step for Int fahr in range(lower, upper, step): Double celcius = 5 * (fahr - 32) / 9 std. ... Read more

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