Carry flag

The carry bit (English carry bit) is a term used in computer science. It indicates a bit which includes the transfer of an addition or subtraction of bits to the next higher order bit.

The measures provided for an elementary computation in a processor values ​​mostly have a fixed memory size, for example n bits with the points a0 to an -1. These values ​​are usually bit by bit edited ( by 1- bit ALUs). A result of the processing of a point ai a result with two points, the higher the priority system digit of the result 1 is the passed as a carry bit to the next ( the higher value) point ai values ​​to be calculated so that this point can be calculated correctly.

The last carry bit of the calculation to the most significant digit of 1 is used by processors often (English carry flag ) stored in a status register as a carry flag, to process, for example in a plurality of computation steps numbers that are greater than the bit width of the ALU. According to the same recursive principle how the n-bit wide numbers calculated from the 1-bit can thus also adding m (m = k * m, k Z ) calculate bit wide numbers.

The carry flag is in principle represents the transfer of the site to- 1, while the overflow depends on the number interpretation and indicates the excess of the applicable speed range.