Write A Function To Determine If A Number Is A Power Of 2

Re:Write A Function To Determine If A Number Is A Power Of 2 by msluyter on Monday October 18, 2010 @12:11PM (#1804012)

Correct me if I'm wrong, but I don't believe the bit twiddling trick would work on floating point representations, would it?

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Re:Write A Function To Determine If A Number Is A Power Of 2 by effigies on Monday October 18, 2010 @12:18PM (#1804045)

With floating point, the first 9 bits are sign and exponent. You could thus check with:

    int ispoweroftwo(float x) {
        return !(*(int*)(&x) << 9);
    }

This only works for exact powers of two, though. It's possible to get something that's really close that will fail this.

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Re:Write A Function To Determine If A Number Is A Power Of 2 by mfukar on Monday October 18, 2010 @12:14PM (#1804026)

Correct, it would not. (I'm assuming IEEE floats)

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