Switching to VOIP saves me $400/year.

Posted on July 10, 2008 by Dennis

T-Mobile came out with a new @Home service at the start of July that integrates VOIP and Wi-Fi calling w/ supported phones. Here’s how it works:

If you carry a plan that is $39/month or more, then you qualify to get the @Home router and they add a line to your account. Your existing phones can plug in to the back of the router (up to two lines) and then you make VOIP calls over your existing high speed internet connection.

Here are some cool details:

  1. Unlimited USA calls from the home line.
  2. Calls made using Wi-Fi with a Wi-Fi capable phone are free which leads to…
  3. You don’t need as many minutes on your plan.
  4. They can port your existing home number over.

We lowered our plan minutes and added the @Home service which left our monthly bill the same. Then we canceled Qwest and are now saving $400/year.

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Formatting Source Code with WordPress

Posted on June 17, 2008 by Dennis

Sometimes you get used to doing things one way and you forget to take a step back now and then and see if there isn’t something you’re missing. In my case, I was formatting source code on this blog by putting html non-breaking spaces and < codes for angle brackets etc. Ouch. What was I thinking.

Here is a much better way to do it. Use the CodeHighLigher plugin. All you have to do after enabling the plugin, is place your source code in a pre tag. Add the lang attribute to the pre tag and you’ll end up with code formatted in a number of languages. The usage section of the plugin document has all the details and languages. I’ll not add that again here. Here is an example though:

 
#include 
int main(int argc, char* argv[]) {
 cout << "Hello Code Formatter Plugin" << endl;
}
< /pre>



You can include code that would otherwise be formatted by the plugin by putting a space between the end angle bracket and the forward slash for the pre tag.  The plugin then outputs the ending pre tag correctly for formatting.


Here is the above code formatted by the plugin:


#include 
int main(int argc, char* argv[]) {
 cout << "Hello Code Formatter Plugin" << endl;
}



Again, I'm not sure why I didn't find this sooner.
Posted in Miscellaneous | Tagged , , , , | 1 Comment

A Good Site To Buy Desktop Computer Memory

Posted on June 14, 2008 by Dennis

A while back, I decided to add extra RAM to my iMac. I had heard from a friend that found a deal for 1G of PC5300 SODIMM for the iMac for as low as $25.00. At the time, I got lucky and found a blowout special at a local retailer for about that price. Now, the same piece of Memory costs over $100.00. Ouch!

Enters the scene: http://www.memorydeal.net. They are focused on providing the correct memory for your system, not just a compatible brand that will work. As I browsed through the different products, I was pleasantly surprised that I could Add IMAC Memory for under the same low price that I originally wanted. Sweet!

MemoryDeal.net has more than just great prices on desktop memory. They also have guides that help you understand what you need to know about adding computer RAM to your system. At the bottom of the home page, you can select the type of system you have, the amount of RAM you want, or a number of other criteria to help you decide exactly what you need to fit in your system. For instance if you need DDR PC2700 Memory, you can check that page, read about the different types and brands they have available, and then see all the appropriate products at the bottom of the page.

Anyway, I may be tempted enough to upgrade from 2 to 4 Gigs in my iMac. Nobody every complained about having a little more memory! MemoryDeal.net conveniently takes their orders through PayPal too. You don’t need to worry about the security of there site or their credit card processor. Just use your PayPal account.

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Timing C/C++ Code on Linux

Posted on June 10, 2008 by Dennis

For my last post, I played around with C++ and a little programming competition. While on the topic, I decided I’d get slightly more serious and enter the next challenge.

One of the things that slightly annoyed me during the process is having to compile/run the program on Windows to enter the competion, while I’m not opposed to this, I do most of my work during the day on a Linux machine and wanted to be able to use that to develop too. For the most part, this isn’t much of an issue because the code is pretty much standard C++ and is quite cross platform compatible. I just generated a Makefile as well as the Visual Studio Project [1] and I can work on the challenge whenever I feel like devoting a little time.

Anyway, the timer code supplied is not cross platform. It only works on Windows. Since it isn’t that complicated, and I wanted to see times on both platforms, I modified the hr_time.h and hr_time.cpp to include an additional implementation for Linux.

Here are the details:

Linux Time Structures

In <sys/time.h>, you get a few functions and structures that make high resolution timing easy. The gettimeofday function returns the seconds and microseconds since the Epoch. The function operates on the timeval structure:

#include 
// snip...
timeval t;
gettimeofday(&t,NULL); // ignoring the 2nd parameter which is the timezone

In addition to being able to query the time, there are also functions for adding, subtracting, and comparing times. For this purpose, the timesub function works perfectly. You need two values (already queried with gettimeofday and and result timeval:

timeval start,stop,result;
// query the start/stop with gettimeofday during your program
timersub(&start,&stop,&result);

result now contains the difference between start/stop in seconds and microseconds.

For the sake of compatibility, the hr_time implementation wants a double for the time, where the fraction part is the number of microseconds. The nice thing is that timesub normalizes tv_usec to somewhere in the range [0,100000). Here is what I did to convert the result to a double:

return result.tv_sec + result.tv_usec/1000000.0; // 1000000 microseconds per second

Here are the completed code files if you’d like to download and look closer or use for yourself:
hr_time.h
hr_time.cpp

Have fun coding!

[1] Actually, I used Bakefile to generate the project files.

Posted in Programming | Tagged , , , | 5 Comments

The Difference Between Dijkstra’s Algorithm and A*

Posted on June 2, 2008 by Dennis

Over the last couple weeks, I’ve had an interest in brushing up my C++ skills. Friday, I came across a programming challenge that looked somewhat interesting and I thought I’d give it a shot.

The object was to find the lowest cost route between 10 cities encoded in a map of integers. Each integer represented the cost to get from that any adjacent location to that spot. This is a classic case of a graph navigation algorithm. Unfortunately, I didn’t have time to test my submission before I had to hand mine in. The deadline was Saturday so I did what I could and turned a solution in before I had to leave Saturday evening.

I ended up with the 3rd best solution for the lowest route and the 2nd best solution for time. I’m not going to discuss Dijkstra’s Algorithm here. You can view the Wikipedia definition or look it up elsewhere if you’re interested in implementing it. I’m simply going to discuss the difference between Dijkstra and A* and show what I could have done with more time to get a top score in the competition.

In Dijkstra’s algorithm you search all the verticies in the graph to determine the lowest cost route between each point. A* is a modification of Dijkstra’s algorithm that uses a heuristic to determine which vertices to search. The heuristic is the estimated cost (or distance) from the node you’re searching to the target node. The lower the heuristic, the more likely you’ll search that node’s edges next instead of some node that is further away. This leads you from the source to the target in a much faster manner. A* allows you to trade off the most accurate result for CPU time.

My route cost was quite a bit higher because I chose a heuristic that was too high. After testing a bit further, I found I could come up with a 2nd place route cost by simply lowering the heuristic a bit. This causes more nodes to be searched, and the algorithm run time to climb, but the result is more accurate. Doing away with the heuristic altogether yields a route cost of 2801, which is the same route cost that the 1st place entry received. The execution time goes up to 36 seconds in that case however. The more accurate Euclidian heuristic (linear distance) yields 2819 and costs 10 seconds.

My 2nd issue was implementation details. I think the algorithm is actually coded correctly but I used data structures that needed constructed and destroyed many times during the algorithm search. I planned on coding the algorithm correctly 1st and then optimizing it but didn’t have time to do the latter. The 1st optimization I’d make is to store node pointers instead of nodes and then only construct a node once during the algorithm’s search cycle. I don’t know if this would have yielded the fastest program or not. Either way, it’ll save a lot of cpu cycles.

Anyway, I accomplished my goal of re-familiarizing myself with lots of STL structures, some iostream details and a few C++ quirks that I hadn’t used or remembered for a while. Perhaps I’ll do better with Challenge 13.

Posted in Programming | Tagged , , , | 1 Comment

GTK+ programs with GtkBuilder and dynamic signal handlers.

Posted on May 22, 2008 by Dennis

Well, I decided to review some GTK+ and Gnome development lately. With GTK+, a nice way to create a user interface is with the Glade Interface Designer. Glade produces an xml file with a glade-interface element that can be loaded by libglade. You can then change attributes of the user interface without having to recompile your program. You just edit the design xml file and you’re good to go. Here are a couple things I noted during the process that weren’t too clear from the documentation:

  1. You have to work with C, not C++, if you want to dynamically load the signal handlers. Many times, it is convenient to write a program mostly in C, but use the C++ compiler and take advantage of a few of the niceties in C++. You can’t do that in this case. According to the libglade documentation, you’ll need to add -export-dynamic flag so that the dynamic loader for the signal handlers can locate the functions in the executable with the gmodule library. That doesn’t work with a C++ compiled executable. You’ll have to stick with C. If you really want to use GTK+ with C++, you can always try the glademm bindings instead of the default C bindings. You could also use gtkmm and write the entire program w/ C++ instead.

    UPDATE: I think you could get around this by using extern “C” around the function calls for the signal handlers. Then you could still use the automatic signal handlers while compiling with g++.

  2. As of GTK+ 2.0, libglade is deprecated. There is a new GtkBuilder interface that does the same thing. You no longer need to compile and link against the libglade libraries. I searched all over for a new interface designer to replace Glade but found a lot of references to people still using Glade. The xml file produced by glade is not exactly the same and not compatible with the GtkBuilder interface however. I finally found that there is a conversion function included with GTK+ 2.0 that converts the glade file to a GtkBuilder xml file.

    gtk-builder-convert <input file> <output file>

Anyway, with those two items taken care of, here is a really simple program and a really simple Makefile I put together to show how to get a GTK+ 2.0 program window showing.

hello.c

#include 
void close_app(GtkWidget* widget,gpointer user_data) {
 gtk_main_quit();
}
int main (int argc, char **argv) {
 GtkBuilder *gtkBuilder;
 GtkWidget *mainwin;
 gtk_set_locale();
 /* Initialize the widget set */
 gtk_init (&argc, &argv);
 /* Create the main window */
 gtkBuilder= gtk_builder_new();
 gtk_builder_add_from_file(gtkBuilder,"hello.ui",NULL); 
 gtk_builder_connect_signals ( gtkBuilder, NULL );
 mainwin= GTK_WIDGET(gtk_builder_get_object(gtkBuilder,"window1"));
 g_object_unref ( G_OBJECT(gtkBuilder) );
 /* Show the application window */
 gtk_widget_show_all ( mainwin );
 /* Enter the main event loop, and wait for user interaction */
 gtk_main ();
 /* The user lost interest */
 return 0;
}

MakeFile
LIBS=$(shell pkg-config --cflags --libs gtk+-2.0)
CFLAGS=-Wall -g -export-dynamic
hello: hello.c hello.ui
    gcc -o hello hello.c $(LIBS) $(CFLAGS)
hello.ui: hello.glade
    gtk-builder-convert hello.glade hello.ui

hello.glade
For the sake of space, I’ll leave the xml contents out. Suffice it to say that there is a window, “window1”, and I set the destroy handler to “close_app”.

The Makefile converts hello.glade to hello.ui, which is loaded by the hello program at runtime to produce the UI. You can of course build a window dynamically at runtime and you can also choose to connect the signal handlers manually. It just struck me as a lot less C code to do it like this.

Posted in Programming | Tagged , , , , , , , | 4 Comments