The Cutest Littlest Forkbomb

February 24, 2015

In one of his last tweets @levans posted the cutest Rust-lang fork bomb:

fn main(){std::thread::spawn(main);main()}

at 42 characters longs, which he sees like a sign. Excluding headers, you can do even shorter in C++:

main(){boost::thread x(main);main();}

It’s not really a terrifying forkbomb (as Linux, for e.g., kills everything after a while because processes run out of memory), and we could have done much worse with a process-level (rather than a thread-level) forkbomb:

main() { fork(); main(); }

This variant creates separate processes… none of which individualy can exhaust its memory! Don’t try this one on your main box (but it could be fun in a virtual machine).

bobomb


No post today

February 17, 2015

I’ve been insanely busy elsewhere lately, so no blog post today ¯\_(ツ)_/¯ .


Easy Timestamping with Bash

February 10, 2015

Here’s a quick Bash script to prefix lines read from standard input by a time stamp.

#!/usr/bin/env bash

while read line
do
    echo $(date "$@") "$line"
done

This script takes the same arguments as the traditional Unix date program. With no arguments, it prints some default-formatted date, but if you feel like it, you can pass it the same arguments as date. For example:

.../geolocalisation> cat /dev/ttyACM0 | ts.sh +"%H:%I:%M:%S.%N" | grep GPRMC | tee $(date | tr \  - | tr : - ).dat
15:03:42:57.355437828 $GPGGA,204226.000,4821.6737,N,06844.4790,W,1,08,1.2,-0.9,M,,,,00$GPRMC,204247.000,A,4821.6740,N,06844.4799,W,0.00,181.2,060215,,*2B
15:03:42:57.629415235 $GPRMC,204248.000,A,4821.6740,N,06844.4799,W,0.00,181.2,060215,,*24
15:03:42:57.881812555 $GPRMC,204249.000,A,4821.6740,N,06844.4800,W,0.00,181.2,060215,,*2A
15:03:42:58.150091204 $GPRMC,204250.000,A,4821.6740,N,06844.4800,W,0.00,181.2,060215,,*22
15:03:42:58.420285771 $GPRMC,204251.000,A,4821.6740,N,06844.4800,W,0.00,181.2,060215,,*23
15:03:42:58.682492676 $GPRMC,204252.000,A,4821.6740,N,06844.4800,W,0.00,181.2,060215,,*20

So Let’s examine the script more closely. The $@ passed as argument to date is the series of all arguments passed to the script. Why is it enclosed in quotes? Because it preserves the structures of the arguments passed to the script for date. In the specific case of date it might not be necessary because of the nature of its arguments, but should you replace date with some other command, it may cause problems to remove the quotes. The $line is also enclosed in quotes because otherwise the script misbehaves: it would, for example, try to expand *.


Comparing GPSes (yet more GPS data)

February 3, 2015

In a few other entries, I’ve toyed with GPS, either getting or parsing the data with Bash, assessing or using the GPS data. However, when we use GPS, we suppose that the precision varies by brand and model&mdashsome will have greater precision—but our intuition tells us that two GPS devices of the same brand and model should perform identically. That’s what we’re used to with, or at least expect from, computers. But what about USB GPS devices?

162px-Gray_compass_rose.svg

So I got two instances of the same model+brand GPS. Let them call them GPS-1 and GPS-2. Do they perform similarly?

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Unfair Coin Tossing

January 27, 2015

Suppose you want a fair coin, one that yields heads and tails with equal probability, but only have a bizarre coin that yields a side more often than the other. Can we remove the bias?

coin-obverse-small

John von Neumann gave us a surprisingly simple procedure to remove bias from a coin and yield a fair toss.

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Building a Book Scanner (Part II: Tray)

January 20, 2015

Last week, I showed how I built the lectern for my book scanner prototype. This week, let’s have a look at the tray holding the glass needed to keep the book evenly opened.

book_stack

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Building a Book Scanner (Part I: Lectern)

January 13, 2015

I’ve been thinking of making my own book scanner for a while now. Since only thinking about something doesn’t get you anywhere, I’ve actually started building it.

book_stack

But before we get to the building of the device—still in progress—let me explain by design goals. The first and foremost goal is that the scanner has to be book-friendly. If you’re going to destroy the book, you might as well use a bandsaw and cut its back off, and use a paper-feed scanner of some sort. So to avoid damage, the lectern on which the book will rest has to be soft, and avoid the need to split the book open.

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