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Boolean NOT
summary
This subchapter looks at Boolean NOT.
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Boolean NOT
This subchapter looks at Boolean NOT.
Please note the differences between a logical Boolean operation, an integer Boolean operation, and a bit-wise Boolean operation.
NOT
NOT (also called negation or complement) simply reverses the value of an object, changing true into false and changing false into true.
The truth table for NOT is as follows:
| A | result |
|---|---|
| 0 | 1 |
| 1 | 0 |
The NOT gate (or inverter) in logic circuits looks like:
As in ordinary algebra, in mixed expressions, all ANDs (Boolean multiplication) are performed before ORs (Boolean addition). For example, A+B·C is evaluated by ANDing B with C and then ORing A with the result of the first operation (BC).
Parenthesis can be used to change the ordinary order of evaluation. For example, (A+B)·C is evaluated by ORing A with B and then ANDing C with the result of the first operation (A+B). Parenthesis can be used for clarity.
Negation of a single variable or object is done before using the result in an expression. Negation of an entire expression is done after the expression is evaluated.
assembly language instructions
Logical instructions typically work on a bit by bit basis, although some processors use the entire contents of the operands as whole flags (zero or not zero input, zero or negative one output). Typical logical operations include logical negation or logical complement (NOT), logical and (AND), logical inclusive or (OR or IOR), and logical exclusive or (XOR or EOR). Logical tests are a comparison of a value to a bit string (or operand treated as a bit string) of all zeros. Some processors have an instruction that sets or clears a bit or byte in registers or memory based on the processor condition codes.
- NOT Logical Complement; Motorola 680x0, Motorola 68300; calculates the one’s complement (logical negation) of the contents of memory or a register (8, 16, or 32 bits); sets or clears flags
- NOT One's Complement Negation; Intel 80x86; calculates the one’s complement (logical negation) of the contents of memory or a register (8, 16, or 32 bits); does not modify flags
See also Logical Instructions in Assembly Language
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