C++ count_bits

[codesafer]

template< class T >

auto    count_bits( T val )

{

    using R = make_unsigned_t< T >;

    const R mask_x55 = ~R( 0 ) / 0x03;

    const R mask_x33 = ~R( 0 ) / 0x0F * 0x03;

    const R mask_x0F = ~R( 0 ) / 0xFF * 0x0F;

    const R mask_x01 = ~R( 0 ) / 0xFF;

    const R to_MSB   = ( sizeof( R ) - 1 ) * CHAR_BIT;

    R v = R( val );

    v = v - ( ( v >> 1 ) & mask_x55 );

    v = ( v & mask_x33 ) + ( ( v >> 2 ) & mask_x33 );

    v = v + ( v >> 4 ) & mask_x0F;

    return  v * mask_x01 >> to_MSB;

}

[씨알메리]

이게 머얌 무서어