**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]      │
└─────────┴──────────────┘
```

{
        unalignedStore<UInt64>(buf, 0);
        unalignedStore<UInt64>(buf + 8, 0x00000000FFFF0000ull | (static_cast<UInt64>(ntohl(in)) << 32));
    }
};
class FunctionToIPv4 : public FunctionIPv4StringToNum
{
public:
    static constexpr auto name = "toIPv4";
    static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionToIPv4>(); }
    String getName() const override
    {
        return name;
    }
    size_t getNumberOfArguments() const override { return 1; }
    DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
    {
        if (!isString(arguments[0]))
            throw Exception("Illegal type " + arguments[0]->getName() + " of argument of function " + getName(),
            ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
        return DataTypeFactory::instance().get("IPv4");
    }
};
class FunctionToIPv6 : public FunctionIPv6StringToNum