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

Why have undefined behavior?

The obvious question that arises from the last section is, why does the standard have UB at all? Why doesn't it specify the result for every situation? A slightly subtler question that acknowledges the reality that C++ is used on a wide variety of hardware with very different properties is this: why doesn't the standard fall back on implementation-defined behavior instead of leaving it undefined?

The last example from the previous section provides us with a perfect demonstration vehicle for the rationale behind the existence of UB. The statement is that an infinite loop is UB; another way of saying that is that the standard does not require a specific outcome from a program that enters an infinite loop (the standard is more nuanced than that, and some forms of infinite loops will cause the program to hang, but these details are not important at the moment). To understand why the rule is there, consider the following code:

size_t n1 = 0,...