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Meaning of NOT-A-NUMBER

Computing Dictionary

(NaN) An ieee floating point representation for the result of a numerical operation which cannot return a valid number value. A NaN can result from multiplying an infinity by a zero, or from subtracting one infinity from another.

NaN is encoded as a special bit pattern which would otherwise represent a floating-point number. It is used to signal error returns where other mechanisms are not convenient, e.g. a hardware floating-point unit and to allow errors to propagate through a calculation.

Similar bit patterns represent positive and negative overflow and underflow and the positive and negative infinities resulting from division by zero.

bit patterns.

[ANSI/IEEE Std 754-1985].