Bit Aligning for Space and Performance Boosts

Question

In the book Game Coding Complete, 3rd Edition, the author mentions a technique to both reduce data structure size and increase access performance. In essence it relies

Answer 1

The compiler is going to either optimize for size or speed and unless you explicitly tell it you wont know what you get. But if you follow the advice of that book you will win-win on most compilers. Put the biggest, aligned, things first in your struct then half size stuff, then single byte stuff if any, add some dummy variables to align. Using bytes for things that dont have to be can be a performance hit anyway, as a compromise use ints for everything (have to know the pros and cons of doing that)

The x86 has made for a lot of bad programmers and compilers because it allows unaligned accesses. Making it hard for many folks to move to other platforms (that are taking over). Although unaligned accesses work on an x86 you take a serious performance hit. Which is why it is important to know how compilers work both in general as well as the particular one you are using.

having caches, and as with the modern computer platforms relying on caches to get any kind of performance, you want to both be aligned and packed. The simple rule being taught gives you both...in general. It is very good advice. Adding compiler specific pragmas is not nearly as good, makes the code non-portable, and doesnt take much searching through SO or googling to find out how often the compiler ignores the pragma or doesnt do what you really wanted.