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When adding two unsigned registers of the same size, an overflow occurs when the carry flag is set. (The term 'carry' is normally used for unsigned overflow, so the term 'overflow' itself can be used for the signed overflow specifically; but, it is valid to use the same word for unsigned arithmetic too.)

The inclusive definition of signed overflow is as follows: When adding two signed (2's complement) registers of the same size, an overflow occurs when both operands have the same sign but the result has the opposite sign. The less inclusive definition is this: When adding two signed registers of the same size, and both of them are positive, and the result is negative, an overflow occurs. The less inclusive definition is useful for distinguishing between the two different types of wraparound, and an underflow is defined as being when adding two negative registers gives a nonnegative result. This makes the word 'overflow' the signed equivalent of the 'carry', and the word 'underflow' the signed equivalent of the 'borrow'.

When using multiple-word signed arithmetic, treat every word except for the most significant as if they were unsigned, use the carry and borrow as normal, and treat only the most significant word as being signed.

O`ver*flow" (?), v. t. [imp. & p. p. Overflowed (?); p. pr. & vb. n. Overflowing.] [AS. oferflwan. See Over, and Flow.]


To flow over; to cover woth, or as with, water or other fluid; to spread over; to inundate; to overwhelm.

The northern nations overflowed all Christendom. Spenser.


To flow over the brim of; to fill more than full.


© Webster 1913.

O`ver*flow", v. i.


To run over the bounds.


To be superabundant; to abound.



© Webster 1913.

O"ver*flow` (?), n.


A flowing over, as of water or other fluid; an inundation.



That which flows over; a superfluous portion; a superabundance.



An outlet for the escape of surplus liquid.

Overflow meeting, a meeting constituted of the surplus or overflow of another audience.


© Webster 1913.

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