Author Archives: dave

FreeNATS new virtual appliance trial

Only a mere six years in the planning and five since the release of a corrupted version, a new FreeNATS virtual appliance is available as a trial.

The new VM (Version 6 Alpha Release Candidate One, 6a RC1) is based on the Turnkey LAMP appliance which is built on Debian LTS.

At the moment this is very much a trial so don’t replace your current VM for production use. All feedback is much appreciated, particularly including use in non-VMWare Player environments e.g. ESX, Virtual Box, Hyper-V etc etc which, fingers crossed, it should import into ok.

So any feedback at all, even just a: worked fine on X version Y would be marvellous.

The URL for the wiki page on the trial including a download link is:

Good luck!

Purplepixie on Facebook

In amazing news Purplepixie Systems, purveyors of shoddy freeware such as FreeNATS and PHPDNS, have come fashionably late to the party and have a Facebook page!


You are now free to go and like (or dislike) our page, which is also where you can chat to us for support/questions/comments on any of the Purplepixie products. This may be especially useful as forum registrations are still disabled and little progress is being made on getting it back online.

We can be found in this amazing new world of social media wonder at:

PHPDNS 1.05 Released

The latest version of PHPDNS version 1.05 is now available for download.

This release version wraps up changes from versions 1.04 and 1.05; mainly a fsockopen timeout bug and a typo.

1.05 has been available on the PHPDNS SCM on github for a while and with no errors reported is now available as the general download.

For anyone interested the bleeding edge releases (and source code in an easily-forkable form) is found at:

PHPDNS Main site and downloads:

Working With Big Numbers

Recently a friend asked me a some questions:

“97 raised to the power of 242 has equalled infinity on every calculator I’ve used, but it’s not infinite just very big. Why do they say infinity? And what is 97^242?”

The answer to the first part is easy; precision (and hence maximum values) are limited. Since this isn’t a basic intro to binary and computing we won’t go into it but just say in the good old days this would have resulted in the number simply wrapping. Modern devices and systems detect this overflow and show a special case result, usually Infinity/Inf or sometimes Not-a-Number/NaN.

Big number calculation in R

97^242 in R

96^242 in Matlab

97^242 in Matlab

Above are two common tools (R and Matlab) both running on 64-bit Linux and overflowing for 97^242. The difference in overflow can be seen in that the OSX Calculator can handle 97^71 but overflows at 96^72, whereas both Matlab and R will handle 97^166 but not 97^156.

Ok well Google has a calculator function so maybe we can just ask it for 97^242?

Google for 97^242

Google for 97^242

Alas, no. But maybe if we trick it with 97+242 to get it’s calculator up and then use that?

Google calculator

97^242 in Google Calc

Nope. So how do we go about trying to calculate 97^242?

There are approaches we can use to estimate it (one of the most promising being looking for differences between powers of 100 and 97 then extrapolating, maybe something for another blog post) but we want an exact answer. As shown by Matlab/R and common logic built-in types are just too small and will overflow.

The solution comes, as with so much in life, from GNU in the GNU Multiple Precision Arithmetic Library aka GNU MP Bignum.

Once installed (yum install gmp-devel on Fedora) it’s just a case of hacking together some C to calculate the result (note the below isn’t supposed to be efficient, more transparent):

Build this with: gcc bignum.c -lgmp -o bignum

And voila:

Answer: 6291579554172660514180168586029512181759771859911909633079235697774386086528343277488812886056338013920280508647975158853848809035553070842805751211101339655910548731303652360707362342079349547320620109301210997985503312350525910702941569606402987567610468491227904389508486082138580406254059512446817845870945561908178074689723504831108854735558785367285467641732532222094514773911007516550984383178257067496267923472962067697340265687768345831925754550553895144516227499602812609

Which for those who can’t be bothered to count digits is rounded as 6.29E+480.

Though of course after all this loading of libraries and writing of C it turns out that although Google couldn’t answer it, naturally Wolfram|Alpha could:

Wolfram Alpha Calculation

Wolfram|Alpha Calculates 97^242 with Ease!


PHPDNS, the open source direct DNS query API for PHP, now has its development source code hosted on

Packaged releases (and release source code versions) will continue to be distributed directly from the PHPDNS web site.

The source code management (SCM) repository for development code can be found at:

All Purplepixie projects hosted on github can be found at:

C/C++ CGI File Upload

A long time ago when I still had (some) hair and hadn’t bitten the PHP bullet I played around with C++ CGIs. Owing to a lack of then available HOW-TO docs I went on to write a (badly written and error-filled) CGI in C/C++ HOW-TO and also a CGI Variable Wrapper. The HOW-TO did what it said on the tin and the wrapper provided an easy API to read/write GET and POST variables as well as cookies.

Surprisingly both the HOW-TO and the wrapper are still in use and I get contacted form time to time with queries. The most common query regards file upload which the wrapper doesn’t support. To illustrate a simple file upload I cobbled together a quick and dirty C example which I’ve provided via email ever since.

So here, for general reference, is my demonstration C code. Please note this is very untested and unrobust, even dodgier than my usual fare. I keep meddling with the idea of finding time to do a proper job either of a standalone file upload API or integrating support into the CGI wrapper. All of this is really just for kicks though as there are better solutions available.


Forum Enabled for New Registrations

A while back I was forced to disable registrations to the Purplepixie Support Forum thanks to a massive quantity of spam, most of which was of a very unseemly nature (very very unseemly).

Following an update to the Purplepixie Forum phpBB and enabling of reCAPTCHA I’ve now re-enabled user registration.

Apologies to anyone who’s had difficulty getting support and had to end up emailing me directly, but I hope the new changes will allow the forum to operate from now on.


Variable Length Arguments in C++, Java, and PHP

Normally in software development we define methods with a given number of parameters (and their type in some languages). Quite often however we want to be able to deal with different numbers of arguments and there are two widely used approaches; different methods and default parameters.

Different methods relies on the concept that the call to function is matched not just on the name of the method but also the count (and type if applicable) of the parameters. So if we wanted a method that could accept one or two integers in C++ we could define two methods:

So if we called SomeFunction(1) the first would be used, SomeFunction(1,2) would use the second.

Default parameters allows us to define some of the parameters as optional and their default values if not passed so the definition:

Would accept one or two integer parameters. SomeMethod(1,2) would have a=1 and b=2 whereas SomeMethod(1) would use the default value and so b=0.

This is all very good and highly useful in a variety of situations but suppose you wanted to handle any number of parameters, from a very small set (or zero) to a large number. Using either of these techniques would require a lot of additional coding, creating a method for each length or the longest set of default parameters imaginable.

This is where the concept of variable length arguments for a method comes in; we want to be able to define a method and accept an arbitrary number of arguments which it can process (please note in most if not all cases the best option for this would be to pass something like a Vector in C++ or an array in PHP, but best practice is not the point of the exercise).

Let’s consider a problem.

We want to have a LineShape function. This function takes a series of Points (a simple class just containing an X and Y coordinate). In a proper system it would then start with the first point and draw a line to each consecutive one but for our example we just want it to print a list of the points it will draw to/from in order.

This could be two points (a single line) or a complex shape of an undetermined total number of points (again note the caveat above that a Vector/List/Array would be the best and safest way to do this in TRW).

So for our implementation we need:

  • A simple Point class
  • A method (LineShape) that takes an arbitrary number of Points and prints out the coordinates
  • Code to create a set of Points and pass them to LineShape

How to do this varies from language to language and, as you might assume, it’s hardest and most dangerous in C++ (because of it’s lack of type safety), slightly easier in Java and PHP (Java because of it’s high type safety and PHP because of it’s lack of any enforced typing).

Variable Length Arguments in C++

To implement in C++ we make use of the va_ functionality provided in stdarg.h. The function is defined as taking the number of parameters passed (int) and then the parameters themselves represented by “…”.

We read the parameter count and then iterate through reading each in turn with va_arg and specifying the type to be used. Note in C++ you must specify the number of parameters being passed when calling the method.

There you have it in C++ (well actually using C libraries); but don’t do it (see above).

Variable Length Arguments in Java

In Java it’s a lot easier as the functionality is built-in to the language. Additionally you don’t need to pass the number of parameters and also the type is determined for the entire set of parameters (in our case Point).

Note that in order for Point to be instantiated as non-static it must be in a seperate file (

So our Point class is:

And the main contains:

So in Java we just need to declare a method with Type… name and then iterate through the array in a for loop.

Variable Length Arguments in PHP

PHP isn’t quite as built-in as Java (an actual language construct) but PHP natively provides functions to support variable length parameters to methods such as func_num_args (number of arguments) and func_get_args (arguments as an array).