Rounding up to next power of 2
Check the Bit Twiddling Hacks. You need to get the base 2 logarithm, then add 1 to that. Example for a 32-bit value:
Round up to the next highest power of 2
unsigned int v; // compute the next highest power of 2 of 32-bit vv--;v |= v >> 1;v |= v >> 2;v |= v >> 4;v |= v >> 8;v |= v >> 16;v++;
The extension to other widths should be obvious.
next = pow(2, ceil(log(x)/log(2)));This works by finding the number you'd have raise 2 by to get x (take the log of the number, and divide by the log of the desired base, see wikipedia for more). Then round that up with ceil to get the nearest whole number power.
This is a more general purpose (i.e. slower!) method than the bitwise methods linked elsewhere, but good to know the maths, eh?
I think this works, too:
int power = 1;while(power < x) power*=2;And the answer is power.