ceph/src/boost/libs/heap/include/boost/heap/detail/ilog2.hpp

   1 // boost heap: integer log2
   2 //
   3 // Copyright (C) 2010 Tim Blechmann
   4 //
   5 // Distributed under the Boost Software License, Version 1.0. (See
   6 // accompanying file LICENSE_1_0.txt or copy at
   7 // http://www.boost.org/LICENSE_1_0.txt)
   8
   9 #ifndef BOOST_HEAP_DETAIL_ILOG2_HPP
  10 #define BOOST_HEAP_DETAIL_ILOG2_HPP
  11
  12 #include <string> // std::size_t
  13
  14 namespace boost {
  15 namespace heap {
  16 namespace detail {
  17
  18 template <typename IntType>
  19 struct log2
  20 {
  21     IntType operator()(IntType value)
  22     {
  23         IntType l = 0;
  24         while( (value >> l) > 1 )
  25             ++l;
  26         return l;
  27     }
  28 };
  29
  30 #ifdef __GNUC__
  31 template<>
  32 struct log2<unsigned int>
  33 {
  34     unsigned int operator()(unsigned int value)
  35     {
  36         return sizeof(unsigned int)*8 - __builtin_clz(value - 1);
  37     }
  38 };
  39
  40 template<>
  41 struct log2<unsigned long>
  42 {
  43     unsigned long operator()(unsigned long value)
  44     {
  45         return sizeof(unsigned long)*8 - __builtin_clzl(value - 1);
  46     }
  47 };
  48
  49 #endif
  50
  51 } /* namespace detail */
  52
  53
  54 template <typename IntType>
  55 IntType log2(IntType value)
  56 {
  57     detail::log2<IntType> fn;
  58     return fn(value);
  59 }
  60
  61 } /* namespace heap */
  62 } /* namespace boost */
  63
  64 #endif /* BOOST_HEAP_DETAIL_ILOG2_HPP */