I wish to count the number of places to the most significant bit in an unsigned integer.
For example
unsigned int i = b0000 1010 0110; // not proper C, b = binary representation
^ MSB: number of places is 8
This is equivalent to counting the number of >>= operations required to obtain 0.
This is useful in algorithms which allocate storage on a 'power-of-2' basis. ie; if one requests 6 elements, 8 are allocated, if one requests 8 elements, 8 are allocated, if one requests 9 elements, 16 are allocated.
(Note: To obtain that allocation scheme, one must decrement by 1 first.)
Is there a faster way to do this operation with bit-hacks? My "simple" method just counts the number of shift-left operations required to obtain 0. (ie; my algorithm has a counter c, which is incremented in a loop while >>= is called repeatedly.)
The actual code I use is the following.
size_t nextpow2(size_t size)
{
if(size == 0)
return 0;
-- size;
size_t c = 0;
for(; size != 0; size >>= 1, ++ c);
return (1 << c);
}
I should add that I need to do this in a cross-platform manner. ie; the code must compile on GCC and Visual Studio 2013.
