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Changed precalculated sqrt(2) values selection to use enable_if.

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[SVN r41282]
This commit is contained in:
Ion Gaztañaga
2007-11-21 16:39:48 +00:00
parent 44f7a47914
commit f6d9bb7b78
1 changed files with 13 additions and 11 deletions
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24
include/boost/intrusive/detail/utilities.hpp
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@@ -515,33 +515,35 @@ inline std::size_t ceil_log2 (std::size_t x)
return ((x & (x-1))!= 0) + floor_log2(x); return ((x & (x-1))!= 0) + floor_log2(x);
} }
template<std::size_t N> template<class SizeType, std::size_t N>
struct numbits_eq
{
static const bool value = sizeof(SizeType)*CHAR_BIT == N;
};
template<class SizeType, class Enabler = void >
struct sqrt2_pow_max; struct sqrt2_pow_max;
template<> template <class SizeType>
struct sqrt2_pow_max<32> struct sqrt2_pow_max<SizeType, typename enable_if< numbits_eq<SizeType, 32> >::type>
{ {
static const boost::uint32_t value = 0xb504f334; static const boost::uint32_t value = 0xb504f334;
static const std::size_t pow = 31; static const std::size_t pow = 31;
}; };
#ifdef BOOST_HAS_LONG_LONG template <class SizeType>
struct sqrt2_pow_max<SizeType, typename enable_if< numbits_eq<SizeType, 64> >::type>
template<>
struct sqrt2_pow_max<64>
{ {
static const boost::uint64_t value = 0xb504f333f9de6484ull; static const boost::uint64_t value = 0xb504f333f9de6484ull;
static const std::size_t pow = 63; static const std::size_t pow = 63;
}; };
#endif
// Returns floor(pow(sqrt(2), x * 2 + 1)). // Returns floor(pow(sqrt(2), x * 2 + 1)).
// Defined for X from 0 up to the number of bits in size_t minus 1. // Defined for X from 0 up to the number of bits in size_t minus 1.
inline std::size_t sqrt2_pow_2xplus1 (std::size_t x) inline std::size_t sqrt2_pow_2xplus1 (std::size_t x)
{ {
const std::size_t value = (std::size_t)sqrt2_pow_max<sizeof(std::size_t)*CHAR_BIT>::value; const std::size_t value = (std::size_t)sqrt2_pow_max<std::size_t>::value;
const std::size_t pow = (std::size_t)sqrt2_pow_max<sizeof(std::size_t)*CHAR_BIT>::pow; const std::size_t pow = (std::size_t)sqrt2_pow_max<std::size_t>::pow;
return (value >> (pow - x)) + 1; return (value >> (pow - x)) + 1;
} }