Lesson 3: Boolean Logic
Unary and Binary Operators
| Symbol |
Usage |
Binary Operation |
| & |
A & B |
AND |
| | |
A | B |
OR |
| ^ |
A ^ B |
XOR |
| ~ |
~A |
NOT |
Figure 3-1 Table of Boolean Operators
Unary and binary operators only are usable within expressions. Expressions are evaluated during assembly of the program and are useful in making the
code easier to understand, usually by breaking up constants into smaller units which are easier to understand. For example, if B is in actuality "going
to the beach and it is sunny outside", then it may be broken up into an equivalent statement. If C is "going to the beach" and D is "it is sunny outside",
then the expression C&D is equivalent to B. Though very helpful in some situations, use of expressions for runtime calculations should be avoided.
Instructions should be used for runtime calculations.
| MOV A, B |
MOV A, C&D |
B = "going to the beach
and it is sunny outside"
(B is a constant)
|
C = "going to the beach"
D = "it is sunny outside"
(C and D are constants)
|
Fig 3-2 Equivalent Statements
Instructions
| Instruction |
Parameters |
Meaning |
| AND |
dest, src |
Logical AND |
| OR |
dest, src |
Logical OR |
| XOR |
dest, src |
Logical XOR |
| NOT |
dest |
Logical NOT |
Figure 3-1 Table of Boolean Operators
Instructions are not evaluated during code assembly as operators are. Therefore, variables may be used in conjunction with constants in the
boolean instructions (except for NOT). For all of the boolean instructions, the Z (zero) flag is set when the result is zero. They are extremely
useful in constructing conditional if/else statements when the if/else directives aren't ideal, such as when cycles must be counted and
synchronized to some outside I/O device.