Re: [boost] A question about static_log2

From: Vesa Karvonen (vesa_karvonen_at_[hidden])
Date: 2003-01-22 20:26:52

Hi,

I'm sorry, but I have too little time to comment more extensively on this 
subject (other duties demand attention). Below you'll find an algorithm, 
that chooses a proper value of n from where to start the log2<> algorithm 
presented earlier. It does not depend on <limits> and it should always 
produce a value that has the correct properties. Feel free to refine it as 
you see fit. You could use it like this:

   template<unsigned long x, int n = detail::choose_n<>::value>
   struct static_log2 {/*...*/};

-Vesa

#include <iostream>

template<int n = 16>
struct choose_n {
private:
  enum {c = 1ul<<n && !(1ul<<n<<n)};
public:
  enum {value = c ? n : choose_n<(c ? 0 : n*2)>::value};
};

template<>
struct choose_n<0> {
  enum {value = 0};
};

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