Archive for December 2009
I wrote a little app to toggle the hiding/showing of hidden files in the OS X Finder, and I’m going to tell you about it. You can find it here (download link) or on my Projects page. The largest part of this application is the icon. The executable file itself is actually just a shell script, the entire source of which is as follows:
#!/bin/sh
if [ `defaults read com.apple.finder AppleShowAllFiles` = "false" ]; then
defaults write com.apple.finder AppleShowAllFiles true
else
defaults write com.apple.finder AppleShowAllFiles false
fi
osascript -e 'tell application "Finder" to quit'
# Finder often tries to open too quickly (causing weird problems)
# so I tell it to wait a second.
sleep 1
osascript -e 'tell application "Finder" to activate'
After seeing that, you might wonder how I got a stupid little shell script all packaged up so nicely in a .app. I’m running low on ideas to blog about, so I guess I’ll explain!
Basically, every OS X application bundle is really just a bunch of files thrown into a folder. The application you see is just a directory with “.app” appended to the end. To view the contents of an app, simply select it in Finder, click the gear in the toolbar, and select “Show Package Contents”. The two things needed to make an application run are the executable (which resides at MyAppName/Contents/MacOS/executablegoeshere) and an Info.plist file. The executable is the code that runs and the Info.plist just tells the OS what everything in the bundle is. If you open up the plist, you’ll see it’s basically an XML document telling the OS what my executable is called, what the icon is called, and giving my app a unique identifier (com.dylanedwards.houdinifile).
I started Project Euler over the Summer and totally forgot about it. The other day I started playing around with ideas of writing a library for integer math with arbitrarily-large numbers in C. As I started writing code, I remember a Project Euler problem (number 13) involving the sum of 100 50-digit numbers that I wanted to solve, so I got some basic arithmetic operations coded and solved it (woohoo, source is now on my Project Euler page).
Anyway, the point of this post is that I wanted to share the code with you. It’s now available here (download link) (moved to http://big-integers.googlecode.com) or on my Projects page. It’s very basic and doesn’t currently support division, comparison, or negative numbers. All of those things (and more!) are coming soon, but I just thought I’d post what I have done. I’ll probably keep updating it (and I’ll post to let you know) over the next week or so.
The algorithms for the three operations that it supports (addition, subtraction, multiplication) are all built off of the basic concepts that we all learned in elementary school. They’re all very simple (the multiplication looks a little confusing at first), and work exactly as if you were solving a problem on paper.
Enjoy!
PS. You can adjust the size (number of digits) of the bignum type in bn.h.
