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

size_t current_size = strnlen(pos_in, n);
                memcpySmallAllowReadWriteOverflow15(pos, pos_in, current_size);
                pos += current_size;
                *pos = '\0';
                out_offsets[i] = ++pos - begin;
                pos_in += n;
            }
            out_vec.resize(pos - begin);
            if (!out_offsets.empty() && out_offsets.back() != out_vec.size())
                throw Exception("Column size mismatch (internal logical error)", ErrorCodes::LOGICAL_ERROR);
            col_res = std::move(col_str);
            return true;
        }
        else
        {
            return false;
        }
    }
    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t ) const override
    {
        const IColumn * column = arguments[0].column.get();
        ColumnPtr res_column;
        if (tryExecuteFixedString(column, res_column) || tryExecuteString(column, res_column))
            return res_column;
        throw Exception("Illegal column " + arguments[0].column->getName()
                        + " of argument of function " + getName(),
                        ErrorCodes::ILLEGAL_COLUMN);
    }
};
class FunctionIPv6CIDRToRange : public IFunction