recursive template at ctfe

[bioinfornatics]

On Tuesday, 26 November 2013 at 21:18:29 UTC, Shammah Chancellor 
wrote:
> On 2013-11-26 21:00:56 +0000, bioinfornatics said:
>
>> On Tuesday, 26 November 2013 at 20:50:13 UTC, bioinfornatics 
>> wrote:
>>> On Tuesday, 26 November 2013 at 20:29:00 UTC, bearophile 
>>> wrote:
>>>> bioinfornatics:
>>>> 
>>>>> I wrote some template to compute at compile time how many 
>>>>> bits is need for a number x. 
>>>>> http://www.dpaste.dzfl.pl/99a842fd
>>>>> 
>>>>> That works for small number but after i got an error about 
>>>>> limit recursion
>>>> 
>>>> Instead of template recursion, have you tried regular code 
>>>> run at compile time?
>>>> 
>>>> http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogObvious
>>>> 
>>>> Bye,
>>>> bearophile
>>> 
>>> Thanks i will take a look
>> 
>> this one seem to be interesting 
>> http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogLookup
>> 
>> is like i do but use a table than me i used a recursive way. I 
>> go to try it :-)
>
> I think you just have a bug in your template code not 
> terminating.   At most you should execute 4 times.   I think 
> there's a problem with casting down from byte to bool.
>
> However, not user if LesserType is what you're after, but this 
> works:
>
> template log2(ulong x)
> {
>  static if( x >> 8 )
>  {
>    enum log2 = log2!(x >> 8) + 8;
>  }
>  else static if( x >> 1)
>  {
>    enum log2 = log2!(x>>1) + 1;
>  } else
>  {
>    enum log2 = 1;
>  }
> }

Thanks your way is much easier to write, works fine :-)