Re: [PATCH] Optimize is_power_of_2().

[Jan Engelhardt <jengelh@computergmbh.de>]

On Jun 15 2007 18:56, Vegard Nossum wrote:
> bool is_power_of_2(unsigned long n)
> {
>-	return (n != 0 && ((n & (n - 1)) == 0));
>+	return n * !(n & (n - 1));
> }

There is a third way which uses neither * nor &&, but []:

bool is_power_of_2(unsigned long n)
{
	static const bool yn[] = {
		[0] = false,
		[1 ... (8 * sizeof(n) - 1)] = true,
	};
	return yn[(n & (n - 1)) == 0];
}



	Jan
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