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

" argument of function " + getName() +
                                ", expected FixedString(" + toString(uuid_bytes_length) + ")",
                                ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
            const auto size = col_in->size();
            const auto & vec_in = col_in->getChars();
            auto col_res = ColumnString::create();
            ColumnString::Chars & vec_res = col_res->getChars();
            ColumnString::Offsets & offsets_res = col_res->getOffsets();
            vec_res.resize(size * (uuid_text_length + 1));
            offsets_res.resize(size);
            size_t src_offset = 0;
            size_t dst_offset = 0;
            for (size_t i = 0; i < size; ++i)
            {
                formatUUID(&vec_in[src_offset], &vec_res[dst_offset]);
                src_offset += uuid_bytes_length;
                dst_offset += uuid_text_length;
                vec_res[dst_offset] = 0;
                ++dst_offset;
                offsets_res[i] = dst_offset;
            }
            return col_res;
        }
        else
            throw Exception("Illegal column " + arguments[0].column->getName()
                + " of argument of function " + getName(),
                ErrorCodes::ILLEGAL_COLUMN);
    }
};
class FunctionUUIDStringToNum : public IFunction