Stop Misquoting Donald Knuth!

Donald Knuth once wrote these unfortunate words:

” We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil.”

This statement is often quoted in an attempt to de-emphasize code performance in favor of other factors which are considered more important:

  • Ease of use
  • Rapid development
  • Clarity and readability
  • Reusability
  • Risk of accidental bugs
  • Extensibility
  • Elegance
  • Object-Oriented Purity

.. The irony about Knuth’s quote is that the people who most often quote it would be horrified by its original context. Knuth made this statement in an article in which he argued in favor of the careful use of go-to statements for micro-optimization in performance-intensive loops


.. The improvement in speed from Example 2 to Example 2a is only about 12%, and many people would pronounce that insignificant. The conventional wisdom shared by many of today’s software engineers calls for ignoring efficiency in the small; but I believe this is simply an overreaction to the abuses they see being practiced by penny-wise- and-pound-foolish programmers, who can’t debug or maintain their “optimized” programs. In established engineering disciplines a 12% improvement, easily obtained, is never considered marginal; and I believe the same viewpoint should prevail in software engineering. Of course I wouldn’t bother making such optimizations on a one-shot job, but when it’s a question of preparing quality programs, I don’t want to restrict myself to tools that deny me such efficiencies.


..  As software engineers, we have largely forgotten about our obligation to create quality programs where efficiency is concerned. We have built for ourselves a culture in which constant factors are the compiler’s problem and the hardware’s problem, in which our productivity, comfort, and profit are more important than the effective utilization of the user’s resources, and the quality of their experience under load.