C# math question: smallest power of 2 bigger than X?

    public int CalcBrackets(int teamCount)
    {
        int positions = 1;

        while (positions < teamCount)
            positions *= 2;

        return positions;
    }

I want the smallest number that is a power of 2 and bigger or equal than teamCount. Is this really开发者_开发百科 the best way to do it? It sure looks horrible :(

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If you need to calculate the least power of 2 (not the multiple) smaller then teamCount, then possibly it is the best way. Taking logarithm is a costy operation and can take more time then a simple cycle.

upd Here is an algorithm (C++) using bitwise operations (http://aggregate.org/MAGIC/, section Next Largest Power of 2)

unsigned int nlpo2(unsigned int x)
{
    x--; // comment out to always take the next biggest power of two, even if x is already a power of two
    x |= (x >> 1);
    x |= (x >> 2);
    x |= (x >> 4);
    x |= (x >> 8);
    x |= (x >> 16);
    return (x+1);
}

First, it sets all relevant bits of the number to ones (for example, 0x3ff) and then increments it (0x400) to get the power of two.

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That while loop doesn't go over multiples of two, but rather powers of two.

If u really need the multiple just add 1, divide by 2 to get the half part and then multiply back by two:

return ((teamCount+1)/2)*2

so that if it was even then you obtain back the same nuber, while if it was odd, since you add 1 and then divide, you get the next even number.

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Smallest multiple

return (teamCount % 2 == 0 ? teamCount : teamCount + 1);

Smallest power, you can take the log. Something like

2 ** (ceil(log_2(teamCount)))

For suitable ceil and log_2 functions. Your technique is fine though.

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this way is simple enough:

if (teamCount % 2 == 0)
    return teamCount;
else
    return (teamCount + 1);

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Not bigger smaller and if you mean multiple 2*2*2*2* log aritm best way that is use logaritma function in base 2 and round result to lower base.That is if team count equals 35 log 2 base 35 gives you 5,xxx round it to 5.