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

Chapter 11:

  1. Undefined behavior is what happens when a program is executed out of contract: the specification says what the valid inputs are and what the results should be. If invalid input is detected, this is also a part of the contract. If the invalid input is not detected and the program proceeds on the (false) assumption that the input is valid, the results are undefined: the specification does not say what must happen.
  2. In C++, there are two main reasons for allowing undefined behavior. First of all, there are operations that require hardware support or are executed differently on different hardware. It may be very difficult or even impossible to deliver a specific result on some hardware systems. The second reason is performance: it may be expensive to guarantee a specific outcome across all computing architectures.
  3. No, an undefined result does not mean that the result must be wrong. The desired result is also permitted under undefined behavior, it's just not...