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

Using undefined behavior for efficient design

In this section, we are going to talk about UB not as it is specified by the standard and applies to C++, but as it is specified by you, the programmer, and applies to your software. To get there, it is helpful first to consider UB from a different point of view.

All the examples of UB that we have seen so far can be divided into two kinds. The first kind is code such as ++k + k. These are bugs, since such code has no defined behavior at all. The second kind is code such as k + 1, where k is a signed integer. This code is everywhere, and most of the time, it works just fine. Its behavior is well defined except for certain values of the variables.

In other words, the code has implicit preconditions: as long as these preconditions are satisfied, the program is well behaved. Note that in the larger context of the program, these preconditions may or may not be implicit: the program may validate the inputs or intermediate results and...