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Conditional Sum Adder
In electronics, a carry-select adder is a particular way to implement an adder (electronics), adder, which is a logic element that computes the (n+1)-bit sum of two n-bit numbers. The carry-select adder is simple but rather fast, having a gate level depth of O(\sqrt n). Construction The carry-select adder generally consists of ripple-carry adders and a multiplexer. Adding two n-bit numbers with a carry-select adder is done with two adders (therefore two ripple-carry adders), in order to perform the calculation twice, one time with the assumption of the carry-in being zero and the other assuming it will be one. After the two results are calculated, the correct sum, as well as the correct carry-out, is then selected with the multiplexer once the correct carry-in is known. The number of bits in each carry select block can be uniform, or variable. In the uniform case, the optimal delay occurs for a block size of \lfloor \sqrt n \rfloor. When variable, the block size should have a d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adder (electronics)
An adder, or summer, is a digital circuit that performs addition of numbers. In many computers and other kinds of microprocessor, processors adders are used in the arithmetic logic units (ALUs). They are also used in other parts of the processor, where they are used to calculate address space, addresses, database index, table indices, increment and decrement operators and similar operations. Although adders can be constructed for many number representations, such as binary-coded decimal or excess-3, the most common adders operate on binary numbers. In cases where two's complement or ones' complement is being used to represent negative numbers, it is trivial to modify an adder into an adder–subtractor. Other signed number representations require more logic around the basic adder. Binary adders Half adder The half adder adds two single binary digits ''A'' and ''B''. It has two outputs, sum (''S'') and carry (''C''). The carry signal represents an Integer overflow, overflow int ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
