Re: portable way to get highest bit set?

jak <[email protected]> Wed, 11 Oct 2023 22:26:05 +0200

Newsgroups	comp.lang.c,alt.comp.lang.c
Organization	A noiseless patient Spider
Message-ID	<[email protected]>

candycanearter07 ha scritto:
> Hi,
> 
> What is the best/most portable way to get the highest bit set?
> 
> ie. 011010001
> to  010000000

Hi,
I don't think it's the best but the most portable could be the
mathematical approach:

#include <stdio.h>
#include <math.h>

int main()
{
     unsigned long val = 3000, ret;

     ret = (unsigned long)pow(2., (double)(unsigned 
long)(log((double)val) / log(2.)));

     printf("%lu -> %lu", val, ret);

     return 0;
}