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

Unnecessary copying

Unnecessary copying of objects is probably C++ inefficiency #1. The main reason is that it’s easy to do and hard to notice. Consider the following code:

std::vector<int> v = make_v(… some args …);
do_work(v);

How many copies of the vector v are made in this program? The answer depends on the details of the functions make_v() and do_work() as well as the compiler optimizations. This tiny example covers several language subtleties that we will now discuss.

Copying and argument passing

We are going to start with the second function, do_work(). What matters here is the declaration: if the function takes the argument by reference, const or not, then no copies are made.

void do_work(std::vector<int>& vr) {
  … vr is a reference to v …
}

If the function uses pass-by-value, then a copy must be made:

void do_work(std::vector<int> vc) {
  … vc is a copy of v …
...