jmmcg::LIBJMMCG_VER_NAMESPACE::dyn::lookup::count_setbits< NumBits > Struct Template Reference

Count the number of set bits in the input number. More...

#include <count_setbits.hpp>

Public Types
typedef unsigned long long	element_type

Public Member Functions
	BOOST_STATIC_ASSERT ((sizeof(element_type) *8)<=std::numeric_limits< typename cache_t::range_type >::max())

Static Public Member Functions
static	__attribute__ ((pure)) element_type result(element_type num) noexcept(true)
constexpr static float	efficiency () noexcept(true)

Detailed Description

template<u_int8_t NumBits>
struct jmmcg::LIBJMMCG_VER_NAMESPACE::dyn::lookup::count_setbits< NumBits >

Count the number of set bits in the input number.

Because the operator>>() is poorly defined this only works for unsigned types. This is because there may be a sign bit or two's complement representation of the negative number. Then shifting might cause the sign bit to be shifted into the number itself, possibly causing an infinite loop.

Complexity: run-time: O(n/s) where n is at most the number of bits used to represent the input type, and s is the number of bits used to represent the size of the cache. Space: O(s)

Definition at line 223 of file count_setbits.hpp.

Member Typedef Documentation

element_type

template<u_int8_t NumBits>

typedef unsigned long long jmmcg::LIBJMMCG_VER_NAMESPACE::dyn::lookup::count_setbits< NumBits >::element_type

Definition at line 231 of file count_setbits.hpp.

Member Function Documentation

__attribute__()

template<u_int8_t NumBits>

static jmmcg::LIBJMMCG_VER_NAMESPACE::dyn::lookup::count_setbits< NumBits >::__attribute__ ( (pure)  )

inlinestaticnoexcept

A loop-based implementation, using a cache. Note that this implementation assumes that the % and / operations when using divisors that are powers of 2 is fast either because:

• The compiler is a good optimising compiler and can covert the % & / to shift operations or,
• the core has either at least one pipelined execution unit that can perform % and / or two execution units that can each perform either % or /.

Definition at line 240 of file count_setbits.hpp.

BOOST_STATIC_ASSERT()

template<u_int8_t NumBits>

jmmcg::LIBJMMCG_VER_NAMESPACE::dyn::lookup::count_setbits< NumBits >::BOOST_STATIC_ASSERT

(

(sizeof(element_type) *8)<=std::numeric_limits< typename cache_t::range_type >::max()

)

efficiency()

template<u_int8_t NumBits>

constexpr static float jmmcg::LIBJMMCG_VER_NAMESPACE::dyn::lookup::count_setbits< NumBits >::efficiency ( )

inlinestaticconstexprnoexcept

Definition at line 248 of file count_setbits.hpp.

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The documentation for this struct was generated from the following file:

• core/count_setbits.hpp