Ten Ways to Check if an Integer Is a Power Of Two in C

Re:Ten Ways to Check if an Integer Is a Power Of Two in C by Jabbles on Tuesday July 26, 2011 @10:13AM (#2807382)

Because the methods clearly get more complicated. Starting simply and naively and then improving is a perfectly standard way of teaching.

Articles like these, which provide detailed explanation of the methods involved and results of benchmarks help greatly.

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Re:Ten Ways to Check if an Integer Is a Power Of Two in C by esrauch on Tuesday July 26, 2011 @10:44AM (#2807553)

The benchmarks would probably be somewhat misleading in a lot of cases here. I'm fairly certain that most compilers will replace a /2 with >>1 for example, so that isn't really going to end up being reflected when you compile it.

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Re:Ten Ways to Check if an Integer Is a Power Of Two in C by feb on Tuesday July 26, 2011 @11:21AM (#2807729)

That depends on the CPU used. Modern CPU have more arithmetic units than logical units and can perform more divisions than bit shifts. There was a good video presentation of that, but I can't find the link now.

EDIT: http://blogs.msdn.com/b/shawnhar/archive/2007/03/19/a-story-... gives other reasons why multiplications can be faster than bit shifts.

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Re:Ten Ways to Check if an Integer Is a Power Of Two in C by aidenn0 on Tuesday July 26, 2011 @03:12PM (#2808993)

That's multiplies, not divides. Modern CPUs are still faster at shifts than divides, even the pentium4, which lacked a single-cycle shift unit.

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