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

return true;
        }
        else
        {
            return false;
        }
    }
    bool useDefaultImplementationForConstants() const override { return true; }
    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t ) const override
    {
        const IColumn * column = arguments[0].column.get();
        ColumnPtr res_column;
        if (tryExecuteUInt<UInt8>(column, res_column) ||
            tryExecuteUInt<UInt16>(column, res_column) ||
            tryExecuteUInt<UInt32>(column, res_column) ||
            tryExecuteUInt<UInt64>(column, res_column) ||
            tryExecuteString(column, res_column) ||
            tryExecuteFixedString(column, res_column) ||
            tryExecuteFloat<Float32>(column, res_column) ||
            tryExecuteFloat<Float64>(column, res_column) ||
            tryExecuteDecimal<Decimal32>(column, res_column) ||
            tryExecuteDecimal<Decimal64>(column, res_column) ||
            tryExecuteDecimal<Decimal128>(column, res_column))
            return res_column;
        throw Exception("Illegal column " + arguments[0].column->getName()
                        + " of argument of function " + getName(),
                        ErrorCodes::ILLEGAL_COLUMN);
    }
};
class FunctionUnhex : public IFunction