Bitwise logical operators (The GNU Fortran Compiler)

#### 5.1.30 Bitwise logical operators ¶

With `-fdec`, GNU Fortran relaxes the type constraints on logical operators to allow integer operands, and performs the corresponding bitwise operation instead. This flag is for compatibility only, and should be avoided in new code. Consider:

      INTEGER :: i, j
      i = z'33'
      j = z'cc'
      print *, i .AND. j

In this example, compiled with `-fdec`, GNU Fortran replaces the `.AND.` operation with a call to the intrinsic ``IAND` — Bitwise logical and` function, yielding the bitwise-and of `i` and `j`.

Note that this conversion occurs if at least one operand is of integral type. As a result, a logical operand is converted to an integer when the other operand is an integer in a logical operation. In this case, `.TRUE.` is converted to `1` and `.FALSE.` to `0`.

Here is the mapping of logical operator to bitwise intrinsic used with `-fdec`:

Operator | Intrinsic | Bitwise operation
--- | --- | ---
`.NOT.` | `NOT` | complement (see `NOT` — Logical negation)
`.AND.` | `IAND` | intersection (see `IAND` — Bitwise logical and)
`.OR.` | `IOR` | union (see `IOR` — Bitwise logical or)
`.NEQV.` | `IEOR` | exclusive or (see `IEOR` — Bitwise logical exclusive or)
`.EQV.` | `NOT IEOR` | complement of exclusive or (see `IEOR` — Bitwise logical exclusive or)