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The logical AND numerical operator compares two values in respect of their bits. If both bits at a certain position in both values are set, then that bit position is set in the result.
result = firstvalue AND secondvalue
- AND compares the bits of the firstvalue against the bits of the secondvalue, the result is stored in the result variable.
- If both bits are on (1) then the result is on (1).
- All other conditions return 0 (bit is off).
- AND is often used to see if a bit is on by comparing a value to an exponent of 2.
- Can turn off a bit by subtracting the bit on value from 255 and using that value to AND a byte value.
The results of the bitwise logical operations, where A and B are operands, and T and F indicate that a bit is set or not set:
| A | B | NOT B | A AND B | A OR B | A XOR B | A EQV B | A IMP B | |
|---|---|---|---|---|---|---|---|---|
| T | T | F | T | T | F | T | T | |
| T | F | T | F | T | T | F | F | |
| F | T | F | F | T | T | F | T | |
| F | F | T | F | F | F | T | T |
Relational Operations return negative one (-1, all bits set) and zero (0, no bits set) for true and false, respectively. This allows relational tests to be inverted and combined using the bitwise logical operations.
Example 1:
101
AND
011
-----
001
The 101 bit pattern equals 5 and the 011 bit pattern equals 3, it returns the bit pattern 001 which equals 1. Only the Least Significant Bits (LSB) match. So decimal values 5 AND 3 = 1.
Example 2:
11111011
AND
11101111
----------
11101011
Both bits have to be set for the resulting bit to be set. You can use the AND operator to get one byte of a two byte integer this way:
firstbyte = twobyteint AND 255
Since 255 is 11111111 in binary, it will represent the first byte completely when compared with AND.
To find the second (HI) byte's decimal value of two byte INTEGERs use: secondbyte = twobyteint \ 256
Finding the binary bits on in an INTEGER value.
DO
INPUT "Enter Integer value from -32768 to 32767 (Enter quits): ", INTvalue&
IF INTvalue& < -32768 OR INTvalue& > 32767 OR INTval& = 0 THEN EXIT DO
FOR exponent = 15 TO 0 STEP -1
IF (INTvalue& AND 2 ^ exponent) THEN PRINT "1"; ELSE PRINT "0";
NEXT
PRINT " "
LOOP UNTIL INTvalue& = 0 'zero entry quits
Example output for 6055.
0001011110100111
Note: The value of 32767 sets 15 bits. -1 sets all 16 bits. Negative values will all have the highest bit set. Use LONG variables for input values to prevent overflow errors.