Fastest way to test if a number is a power of n?

TangentZ · 2002-02-13T00:43:00

Let''s say you need to find out if a number, m, is a power of another number, n. i.e. Does m = n ^ k for some k? e.g. 2048 is a power of 2 since 2 ^ 11 = 2048 34271896307633 is a power of 17 since 17 ^ 11 = 34271896307633 But 317239 is not a power of 5 It''s not too hard when n = 2. You can build a small table of (1,2,4,8,16,32...1024) if your m is small. Similarly for other cases of n. What about when m is 4 billion? Let''s write a function like this: bool PowerOf(unsigned int m, unsigned int n) { //return true if m is a power of n //return false otherwise } What is the best/fastest way to write this C/C++ function? (No assembly please). Premature optimizations can only slow down your project even more.

Math and Physics Programming

Started by TangentZ February 03, 2002 01:26 PM

30 comments, last by TangentZ 23 years ago

utwo007

122

February 12, 2002 07:25 PM

I have a very quick function, but it only works for powers of 1.

int PowerOfOne(x) { return(1); };

Hope that helps.

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Kippesoep

892

February 13, 2002 12:41 AM

I hate to burst your bubble (actually, I don't), but that's incorrect... It should be:

      int PowerOfOne(x){  return x == 1;};

Because the only thing that is a power of 1 is 1 itself.

Edited by - Kippesoep on February 13, 2002 1:43:00 AM

Kippesoep

Fastest way to test if a number is a power of n?

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