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
function, yielding the bitwise-and of IAND
— Bitwise logical andi
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) |