Erica Sadun put together a great tool for iPhone users who’d like to keep tabs on their iPhone’s location. Instead of GPS tracking, a small binary called ‘findme’ is used to geolocate the device based on nearby cell towers.
Combined with a simple curl shell script, a private Twitter account, and a scheduled launch daemon, your iPhone can then report its location at regular intervals, which you (or anyone you authorize) can follow using Twitter and Google Maps. You could use this to find your phone if it’s lost or stolen, or you might just use it to give your friends and family a way to track your current location.
Related posts:
Command Line Twitter
Open GPS Tracker
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I wonder why these stupid things keep coming up every 5 to 10 years.
Ever thought about cache behaviour ?
Or the fact that an “decrease, compare and jump” is basically free ?
Please take a look at the assembler that gets generated from “Duff’s Device” and then tell me again that it’s a good idea to use it.
Please you young and innocent out there:
Forget that you ever saw this, there is a good reason why it has been buried long time ago.
:)
function duffFasterLoop8(iterations) {
var testVal=0;
for(n = iterations; n > 8; n -= 8)
{
testVal++;
testVal++;
testVal++;
testVal++;
testVal++;
testVal++;
testVal++;
testVal++;
}
do
{
testVal++;
}
while (–n);
}
I’m one of those who re-discovered same optimization several years ago. And it works. Benchmarks show real speed improvements. And it probably worked even better in 1983, when C compilers were really bad.
What about code size and cache issues? As long as code completely fits into L1, who cares?
Nice explanation. People don’t understand that micro-optimizations are still useful. Not every compiler in the world is gcc-like. You may have to use different compilers for different projects, different devices and many compilers need hand-holding to produce better results, even gcc performs better if you provide more info to it. Here is another article about getting compilers to produce better code for loops:
http://www.safercode.com/blog/2009/01/27/tweak-your-code-for-speed-unroll-those-loops-part-1.html