## Archive for April, 2009

Here’s a tip to improve the speed and efficiency of your C programs: BIT OPERATIONS ARE MUCH FASTER THAN BYTE OPERATIONS!!! Let’s say you want to multiply a variable by 2 in your C program. Well, you could do:

variable = variable * 2;

But let’s consider that in order to perform this operation, the system will need to deal with at least two pieces of data: the variable, and the constant 2. It would be nice if there were a way to perform some of these basic math operations without having to deal with multiple data points. Alas, there is:

variable << 1; This simply shifts the bits one to the left. Why does this work? Let's say: 00000100 = 4 Shifting the bits one to the left yields: 00001000 = 8 This is simply an underlying principle of the binary system that computers use. This tip also works in reverse - you don't need to ever divide by two, either! You can just bitshift one to the right! Now, I don't have any empirical evidence at the moment to support this claim numerically, but it's true, the bitshift operations will always run much faster than the numerical operation. The proof is simply logical. Now here's the nugget of the day, as found on an interwebs forum, allegedly from the original K&R C book. It's a simple function to determine if a number is a power of two: if(!(phys_mem_size & (phys_mem_size - 1))) { printf("This number is a power of two."); } How's it work? Consider that a power of two will only have one bit set. It follows, therefore, that subtracting one from it will set that bit to zero, and every bit after it equal to one. Taking the binary and of these values results in something like: 16 = 00010000 15 = 00001111 & = 00000000 The important thing is to reverse the statement, that is, if NOT this and that, since if it is a power of two, a zero will be returned, which is false in C. There's plenty of other operations that can be done in C that can take advantage of the bit-patterns and power-of-two-nature of computers. Such ops can be performed on the mantissa of floats sometimes to produce interesting results that are mathematically correct. Do yourself and your computer a favour - think of this sort of low-level trickery first when trying to solve a problem while programming, it'll help you produce cleaner, faster, and more efficient code, not to mention making it look more professional.

Here’s an interesting concept, and one that’s, rather surprisingly, widely unknown. It’s called tetration, a concept brought up so rarely that most computer dictionaries don’t even recognize it as being a word. I was organizing my filesystem hierarchy today, and found this old paper I wrote for my Discrete Mathematics class. I gave it a quick re-read, and the concepts still amaze me. It is truly impossible to ignore the beauty of mathematics, especially after seeing something like this. Drawing of the analytic extension f = F(x + iy) of tetration to the complex plane.

The basic premise of tetration is simply a continuation of what has already been examined since, well, probably kindergarten. Everyone knows what addition, subtraction, multiplication, and division are. But consider this concept for a moment: multiplication is just repeated addition, exponentiation (x^y) is just repeated multiplication, and tetration, well, that’s just repeated exponentiation! It has other names as well. Since it’s concept looks something like a^b^b^b^b, it has been called a power-tower. It is also interesting to note that we’ve all seen an equation somewhere or another that may have looked something like: a^b^2. Now, the simplest way to solve this would be to start by squaring b, then raising a to that power. But if b were to resolve to a value of two – well, that’s tetration! It’s pretty neat to see how tetration can be often be used, yet is relatively unknown.

And here’s where it starts to get even stickier – it doesn’t stop at tetration! If there’s an operation n, that means that there is an operation n+1 which formulates itself as the repeated nth operation. So that means there’s an infinite number of operations that can be performed on numbers. It’s also crazy to think that there’s an operation at infinity, so that given any non-zero inputs, an infinite value would be returned. There’s a lot of power to be found in tetration and nth-term iterative operators, and oddly enough, if I had to guess that the problem had a solution, I would say this would be a good starting point for which to solve the [Riemann hypothesis].This is some crazy stuff here, and if it’ll help anyone to further understand, I’ve uploaded my findings on tetration to this server for download [here]. Enjoy!

So yeah, I think that I will use this little corner of webspace as my own. Hopefully the posts won’t be absolute rubbish, either. I found this template somewhere online. I kind of like it, let me know if you like it too, please.

Make sure to check back somewhat often – I’ll update it as often as I can, when time permits. That’ll probably happen more over this coming summer, when I have some interesting things to talk about, and spare time.

Enjoy.