Number of Bits Needed to Represent a Zero-Offset Integer

[H. S. Teoh via Digitalmars-d-learn]

On Fri, Feb 13, 2015 at 12:28:23PM +0000, bearophile via Digitalmars-d-learn wrote:
> Dominikus Dittes Scherkl:
> 
> >I would recommend to use something like this:
> >
> >/// returns the number of the highest set bit +1 in the given value
> >/// or 0 if no bit is set
> >size_t bitlen(T)(const(T) a) pure @safe @nogc nothrow if(isUnsigned!T)
> >{
> >   static if(T.sizeof <= size_t.sizeof) // doesn't work for ulong on 32bit sys
> >   {
> >      return x ? core.bitop.bsr(x)+1 : 0;
> >   }
> >   else static if(T.sizeof == 8) // ulong if size_t == uint
> >   {
> >      return x ? x>>32 ? core.bitop.bsr(x)+33 : core.bitop.bsr(x)+1 : 0;
> >   }
> >}
> 
> Is this good to be added to Phobos? Perhaps with a more descriptive
> name?
[...]

Isn't it essentially floor(log_2(a)), mathematically speaking? Maybe
that could be the basis of a better name?


T

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