Dumpyard

Data alignment is an important issue for all programmers who directly use memory. Data alignment affects how well your software performs, and even if your software runs at all. As this article illustrates, understanding the nature of alignment can also explain some of the “weird” behaviors of some processors.

This manual provides an introduction to the GNU C and C++ Compilers, gcc and g++, which are part of the GNU Compiler Collection (GCC). The development of this manual was funded entirely by Network Theory Ltd. Copies published by Network Theory Ltd raise money for more free documentation.

I have written Optimizing C++ because I believe that this common attitude is incorrect, and that a knowledge of optimization is essential to a professional programmer. One very important reason is that we often have little control over the hardware on which our programs are to be run. In this situation, the simplistic approach of adding more hardware is not feasible. Optimizing C++ provides working programmers and those who intend to be working programmers with a practical, real-world approach to program optimization. Many of the optimization techniques presented are derived from my reading of academic journals that are, sadly, little known in the programming community. This book also draws on my nearly 30 years of experience as a programmer in diverse fields of application, during which I have become increasingly concerned about the amount of effort spent in reinventing optimization techniques rather than applying those already developed.

Welcome to smallcode, an educational wiki where you can share your programming tips and contribute to research projects. Old smallcode blog was moved.

It looks as though primes tend to concentrate in certain curves that swoop away to the northwest and southwest, like the curve marked by the blue arrow. On the next few pages of this website, we’ll investigate these patterns and try to make sense out of them.

Linux processes execute in a virtual environment that makes it appear as if each process had the entire address space of the CPU available to itself. This virtual address space extends from address 0 all the way to the maximum address. On a 32-bit platform, such as IA-32, the maximum address is 232 - 1 or 0xffffffff. On a 64-bit platform, such as IA-64, this is 264 -1 or 0xffffffffffffffff.

This is C++ FQA Lite. C++ is a general-purpose programming language, not necessarily suitable for your special purpose. FQA stands for “frequently questioned answers”. This FQA is called “lite” because it questions the answers found in C++ FAQ Lite.

Suppose you run on the x86 and you don’t like its default FPU settings. For example, you want your programs to dump core when they divide by zero or compute a NaN, having noticed that on average, these events aren’t artifacts of clever numerical algorithm design, but rather indications that somebody has been using uninitialized memory. It’s not necessarily a good idea for production code, but for debugging, you can tweak the x86 FPU thusly:

The really short answer is that computers do not have two kinds of storage any more. It used to be that you had the primary store, and it was anything from acoustic delaylines filled with mercury via small magnetic dougnuts via transistor flip-flops to dynamic RAM. And then there were the secondary store, paper tape, magnetic tape, disk drives the size of houses, then the size of washing machines and these days so small that girls get disappointed if think they got hold of something else than the MP3 player you had in your pocket. And people program this way.