Number of Bits Needed to Represent a Zero-Offset Integer

[Dominikus Dittes Scherkl via Digitalmars-d-learn]

On Monday, 19 January 2015 at 21:23:47 UTC, Nordlöw wrote:
> On Monday, 19 January 2015 at 20:54:50 UTC, Steven 
> Schveighoffer wrote:
>> Cool. I would point out that the commented code suggests you 
>> should be handling the 0 case, but you are not (when T.min == 
>> T.max)
>
> I believe that should trigger a failing static assert with a 
> good error message as it doesn't make any sense to call the 
> function in that case. Thanks.

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;
    }
}