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

static inline bool tryParseIPv4(const char * pos)
    {
        UInt32 result = 0;
        return DB::parseIPv4(pos, reinterpret_cast<unsigned char *>(&result));
    }
    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 std::make_shared<DataTypeFixedString>(IPV6_BINARY_LENGTH);
    }
    bool useDefaultImplementationForConstants() const override { return true; }
    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t ) const override
    {
        const ColumnPtr & column = arguments[0].column;
        if (const auto * col_in = checkAndGetColumn<ColumnString>(column.get()))
        {
            auto col_res = ColumnFixedString::create(IPV6_BINARY_LENGTH);
            auto & vec_res = col_res->getChars();
            vec_res.resize(col_in->size() * IPV6_BINARY_LENGTH);
            const ColumnString::Chars & vec_src = col_in->getChars();
            const ColumnString::Offsets & offsets_src = col_in->getOffsets();
            size_t src_offset = 0;
            char src_ipv4_buf[sizeof("::ffff:") + IPV4_MAX_TEXT_LENGTH + 1] = "::ffff:";
            for (size_t out_offset = 0, i = 0; out_offset < vec_res.size(); out_offset += IPV6_BINARY_LENGTH, ++i)
            {