Not-a-Number

mathematics (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 [what else?].

NaN is encoded as a special bit pattern [what 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].

[Correct?]

(2001-04-01)