arithmeticlogic

Arithmetic logic refers to the computational capability of a processor to perform integer arithmetic and bitwise logical operations. In most CPUs, this functionality is realized by the arithmetic logic unit (ALU), a core component of the data path that accepts operands from registers, applies an operation, and writes the result back to a register or memory.

Operations performed typically include addition and subtraction, with multiplication and division included in some designs or handled by separate units. Bitwise logical operations such as AND, OR, XOR, and NOT, as well as bit shifts and rotates, are standard. Many ALUs also perform comparison operations that set processor status flags. Output status bits commonly include zero, carry, sign (or negative), and overflow, which are used for conditional branches and multi-precision arithmetic.

ALUs are implemented as combinational circuits, often built from adders, multiplexers, and logic gates. Modern architectures use wide, pipelined ALUs or multiple parallel units to execute several operations per cycle. Common adder designs include ripple-carry, carry-lookahead, and carry-select variants. Floating-point arithmetic is typically handled by a separate unit, distinct from integer ALUs.

Architecturally, the ALU is controlled by the control unit via the instruction set encoding, mapping opcodes to specific ALU operations. The design of the ALU affects processor speed, power, and area, and influences compiler behavior and microarchitectural decisions such as pipelining and out-of-order execution.

Historically, ALUs evolved from simple adders and logic gates to sophisticated, multi-issue units integrated into modern microprocessors. In educational and practical contexts, arithmetic and logic are described as two fundamental categories of CPU operations used to implement software.