Book Image

The Art of Writing Efficient Programs

By : Fedor G. Pikus
3 (2)
Book Image

The Art of Writing Efficient Programs

3 (2)
By: Fedor G. Pikus

Overview of this book

The great free lunch of "performance taking care of itself" is over. Until recently, programs got faster by themselves as CPUs were upgraded, but that doesn't happen anymore. The clock frequency of new processors has almost peaked, and while new architectures provide small improvements to existing programs, this only helps slightly. To write efficient software, you now have to know how to program by making good use of the available computing resources, and this book will teach you how to do that. The Art of Efficient Programming covers all the major aspects of writing efficient programs, such as using CPU resources and memory efficiently, avoiding unnecessary computations, measuring performance, and how to put concurrency and multithreading to good use. You'll also learn about compiler optimizations and how to use the programming language (C++) more efficiently. Finally, you'll understand how design decisions impact performance. By the end of this book, you'll not only have enough knowledge of processors and compilers to write efficient programs, but you'll also be able to understand which techniques to use and what to measure while improving performance. At its core, this book is about learning how to learn.
Table of Contents (18 chapters)
1
Section 1 – Performance Fundamentals
7
Section 2 – Advanced Concurrency
11
Section 3 – Designing and Coding High-Performance Programs

What is undefined behavior?

The concept of undefined behavior (UB) is shrouded in mystery, complete with arcane warnings for the uninitiated. The Usenet group comp.std.c warns, "When the compiler encounters (an undefined construct), it is legal for it to make demons fly out of your nose." Launching nuclear missiles and neutering your cat (even if you don't own a cat) have been mentioned in a similar context. One of the tangential goals of this chapter is to demystify UB: while the ultimate goal is to explain the relationship between UB and performance and to show how to take advantage of UB, we cannot do that until we can discuss the concept rationally.

First of all, what is UB in the context of C++ (or any other programming language)? There are specific places in the standard where the words the behavior is undefined or the program is ill-formed are used. The standard further says that if the behavior is undefined, the standard imposes no requirements on the results...