Commodore VIC-20 - Page 85

Logical operators work by converting their operands to
sixteen-bit, signed, two's-complement integers in the range
-32768 to -i- 32767. (If the operands are not in this range, an error
results.) If both operands are supplied as 0 or -1, logical operators
return 0 or -1. The given operation is performed on these integers
in bitwise fashion, i.e., each bit of the result is determined by the
corresponding bits in the two operands.
Thus, it is possible to use logical operators to test bytes for a
particular bit pattern. For example, the AND operator may be used
to "mask" all but one of the bits of a status byte at a machine I/O
port. The OR operator may be used to "merge" two bytes to create
a particular binary value. The following examples will demonstrate
how the logical operators work:
63 AND 16 - 16 63 - binary 111111 and 16 = binary
10000, so 63 AND 16=16
15 AND 14 =14 15 - binary 1111 and 14 = binary
1110, so 15 AND 14 = 14 (binary 1110)
-1 AND 8 = 8 -1 = binary 11111111 and 8 =
binary 1000, so -1 AND 8 = 8
4 OR 2 = 6 4 = binary 100 and 2 = binary 10, so 4
or 2 = 6 (binary 110)
10 OR 10 =10 10 = binary 1010, so 1010 OR 1010 -
1010 (10)
-1 OR -2 = -1 -1 m binary 11111111 and -2 = binary
11111110, so
- 1 OR - 2 = -1. The bit complement of
sixteen zeros is sixteen ones, which
is the two's complement representation
of -1.
NOT X= {-X) + 1 The two's complement of any integer is
the bit complement plus one.
STRING OPERATIONS
Strings may be concatenated using + . For example:
10 A$ = "FILE" : B$ = "NAME"
20 PRINT AS - BS
30 PRINT "NEW1 + AS - BS
RUN
FILENAME
NEW FILENAME
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