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. I’m happy about the code coverage, though: As a properly developed software project, it achieves about 96% code coverage - the missing parts happening at the end, when time ran out ;) ... Read more 》

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). The .org domain I had to ACK, which I did at 20:46 and at 03:00 I received the notification that the transfer was successful (I think there was some registrar ACKing involved there). So the whole transfer took about 10 1/2 hours, or 7 hours since I retrieved the auth code. I think that’s quite a good time :) ... Read more 》

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 》

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 》

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.d); and configured hdparm.conf to put my hard disk into standby after 5 seconds (it’s only used for big data anyway, so most of the time it is unused). It now consumes 5W in idle with minimum brightness, and 8-10W with brightness 13 of 15. Consumption when surfing is 10 - 15 watts. Booting from grub to gdm is fast, I did not measure it, but it probably took about 5 seconds. ... Read more 》

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.name == dep.name and best_real is None: best_real = target if target.name != dep.name and best_virtual is None: best_virtual = target if target.is_installed(): return target return best_real if best_real is not None else best_virtual Now, this way of solving dependencies is slightly problematic. Let us consider a package that depends on: a | b, b. APT will likely choose to install ‘a’ to satisfy the first dependency and ‘b’ to satisfy the second. I currently have draft code around for a future version of APT that will cause it to later on revert unneeded changes, which means that APT will then only install ‘b’. This result closely matches the CUDF solvers and cupt’s solver. ... Read more 》

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). To fix this problem, I considered various options. ... Read more 》

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. That is, f() owns the reference to x + 1. In that case, the call to g() would no longer be in a tail call position, as we still have to decrease the reference count after g() exits. ... Read more 》

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? Consider the partially applied form printLn1: ... Read more 》

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.io.printf(io, "%3d\t%6.1f\n", fahr, celcius) It does not really look like it, but this language is purely functional. It represents side effects using unique types. If you declare a mutable parameter, you basically declare a unique input parameter and a unique output parameter. ... Read more 》