recursive template at ctfe

[Shammah Chancellor]

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;
  }
}