**Use case**

Convert bitmask to position.
It would allow us to directly use FLAT dictionary or Enum datatype without jumping around slow `bitmasktoArray` and `arrayMap`

**Describe the solution you'd like**

```
SELECT
    arrayMap(x -> log2(x), bitmaskToArray(100)) AS bitmask,
    bitPositions(100)  AS bitpositions

┌─bitmask─┬─bitpositions─┐
│ [2,5,6] │ [2,5,6]      │
└─────────┴──────────────┘
```

{
private:
#if defined(__SSE2__)
    #include <emmintrin.h>
    static inline void applyCIDRMask(const UInt8 * __restrict src, UInt8 * __restrict dst_lower, UInt8 * __restrict dst_upper, UInt8 bits_to_keep)
    {
        __m128i mask = _mm_loadu_si128(reinterpret_cast<const __m128i *>(getCIDRMaskIPv6(bits_to_keep).data()));
        __m128i lower = _mm_and_si128(_mm_loadu_si128(reinterpret_cast<const __m128i *>(src)), mask);
        _mm_storeu_si128(reinterpret_cast<__m128i *>(dst_lower), lower);
        __m128i inv_mask = _mm_xor_si128(mask, _mm_cmpeq_epi32(_mm_setzero_si128(), _mm_setzero_si128()));
        __m128i upper = _mm_or_si128(lower, inv_mask);
        _mm_storeu_si128(reinterpret_cast<__m128i *>(dst_upper), upper);
    }
#else
    
    static void applyCIDRMask(const UInt8 * __restrict src, UInt8 * __restrict dst_lower, UInt8 * __restrict dst_upper, UInt8 bits_to_keep)
    {
        const auto & mask = getCIDRMaskIPv6(bits_to_keep);
        for (size_t i = 0; i < 16; ++i)
        {
            dst_lower[i] = src[i] & mask[i];
            dst_upper[i] = dst_lower[i] | ~mask[i];
        }
    }
#endif
public:
    static constexpr auto name = "IPv6CIDRToRange";
    static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionIPv6CIDRToRange>(); }