A programming challenge, by Joseph K. Horn

How can you tell, WITH PERFECT ACCURACY, whether or not a number is exactly a
power of 2?

Try it:  Write a program called POW2 which tests whether the number on level 1
is a perfect power of 2, and returns a 1 if true, and a 0 if false.

While enjoying dinner at Sizzler restaurant, a member of our local HP
Calculator Club set this challenge before us.  Everybody came up with a
different answer.  Before you look at mine (POW2 on this disk), come up
with one of your own.  There are a hundred ways to do it; which is best?

By the way, test some difficult cases like 2^4, 2^16, and 2^39.

Have fun!

-jkh-