If the terms to
be
operated
on
are not already integers. they are converted to
integer form; the Boolean operation
is
performed. and the result
is
presented
as
a
single integer value. This
is
also how Boolean operations
work
on
the true/false
expressions. That
is.
there
is
no operational difference between a mixed Boolean
operation such
as:
A=1
OR
C<2
and a simple Boolean operation
su
ch
as:
A
OR
C
The only practical difference
is
that. since a relational expression
is
evalu-
ated to
-1
or
O.
the Boolean operation
will
always
be
performed on quantities of
-1
and 0 for a relational expression. For example:
IF
A=B
AND
C<D
GOTO
40
First the relational expressions are evaluated. Assume
that
the first expression
is
true and the second one
is
false. In effect. the
following
Boolean expression
is
evaluated:
IF
-1
AND 0
GOTO
40
Performing the AND yields a 0 result:
IF
0
GOTO
40
Recall
that
a single term
has
an
implied
"<
>0"
following
it. The expression
therefore becomes:
IF
0<
>0
GOTO
40
Thus. the branch
is
not taken.
ln contrast. a Boolean operation performed
on
two
variables may yield any
integer number:
IF
A% AND
B%
GOTO
40
Assume
that
A%=255
and B%=240. The Boolean operation 255 AND 240 yields
240. The statement. therefore.
is
equivalent to:
IF
240
GOTO
40
or.
with
the
"<
>0":
IF
240 <
>0
GOTO
40
Therefore the branch
will
be
taken.
Now
compare the
two
assignment statements:
A = A
AND
10
A=A<lO
ln the first example. the current value of A
is
logically ANDed
with
10 and
the result becomes the new value of
A.
A must
be
in
the integer range
±32767.
In
the second example. the relational expression A <
lOis
evaluated
to
-1
or
0,
so A
must
end up
with
a value of
-1
or
O.
68
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