Tips for Optimizing C/C++ Code

https://people.cs.clemson.edu/~dhouse/courses/405/papers/optimize.pdf

• Remember Ahmdal's Law. This is often phrased as: "make the common case fast and the rare case correct."
• Code for correctness first, then optimize!
• People I know who write very efficient code say they spend at least twice as long optimizing code as they spend writing code.
• Jumps/branches are expensive. Minimize their use whenever possible.
• Think about the order of array indices.
• Think about instruction-level-parallelism.
• Avoid/reduce the number of local variables.
• Reduce the number of function parameters.
• Pass structures by reference, not by value.
• If you do not need a return value from a function, do not define one.
• Try to avoid casting where possible.
• Be very careful when declaring C++ object variables.
• Make default class constructors as lightweight as possible.
• Use shift operations >> and << instead of integer multiplication and division, where possible.
• Be careful using table-lookup functions.
• For most classes, use the operators += , -= , *= , and /= , instead of the operators + , - , * , and / .
• For basic data types, use the operators + , - , * , and / instead of the operators += , -= , *= , and /= .
• Delay declaring local variables.
• For objects, use the prefix operator `(obj)` instead of the postfix operator `(obj)`.
• Be careful using templates.
• Avoid dynamic memory allocation during computation.
• Find and utilize information about your system’s memory cache.
• Try to early loop termination and early function returns.
• Simplify your equations on paper!
• The difference between math on integers, fixed points, 32-bit floats, and 64-bit doubles is not as big as you might think.
• Consider ways of rephrasing your math to eliminate expensive operations.