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In computing, an arithmetic logic unit (ALU) is a combinational digital circuit that performs arithmetic and bitwise operations on integer binary numbers. [ 1 ] [ 2 ] This is in contrast to a floating-point unit (FPU), which operates on floating point numbers.
It can however in theory also be used to implement unary operations, such as logical shift left, in cases where limited by a fixed amount (e.g. for address generation unit). One way to implement a barrel shifter is as a sequence of multiplexers where the output of one multiplexer is connected to the input of the next multiplexer in a way that ...
The two basic types are the arithmetic left shift and the arithmetic right shift. For binary numbers it is a bitwise operation that shifts all of the bits of its operand; every bit in the operand is simply moved a given number of bit positions, and the vacant bit-positions are filled in.
The ALU (or arithmetic logic unit) has the following input, output and control lines: 2 32-bit input lines: one for the B bus and one for the bus that is connected directly to the H register. 1 32-bit output line, which is connected directly to the shifter. 6 control lines aimed to select which operation to perform.
A data path is a collection of functional units such as arithmetic logic units (ALUs) or multipliers that perform data processing operations, registers, and buses. [1] Along with the control unit it composes the central processing unit (CPU). [1] A larger data path can be made by joining more than one data paths using multiplexers.
Most C and C++ implementations, and Go, choose which right shift to perform depending on the type of integer being shifted: signed integers are shifted using the arithmetic shift, and unsigned integers are shifted using the logical shift. In particular, C++ uses its logical shift operators as part of the syntax of its input and output functions ...
In the 1970s and 1980s, a number of research and commercial computers used bit slicing, in which the CPU's arithmetic logic unit (ALU) was built from multiple 4-bit-wide sections, each section including a chip such as an Am2901 or 74181. The Zilog Z80, although it is an 8-bit microprocessor, has a 4-bit ALU. [11] [12]
GCC and compatible compilers signal the presence of 128-bit arithmetic when the macro __SIZEOF_INT128__ is defined. [10] For the C programming language , 128-bit support is optional, e.g. via the int128_t type, or it can be implemented by a compiler-specific extension.