underflow

programming (or "floating point underflow", "floating

underflow", after "overflow") A condition that can occur

when the result of a floating-point operation would be

smaller in magnitude (closer to zero, either positive or

negative) than the smallest quantity representable. Underflow

is actually (negative) overflow of the exponent of the

floating point quantity. For example, an eight-bit twoscomplement exponent can represent multipliers of 10^-128 to

10^127. A result less than 10^-128 would cause underflow.

Depending on the processor, the programming language and the

run-time system, underflow may set a status bit, raise an

exception or generate a hardware interrupt or some

combination of these effects. Alternatively, it may just be

ignored and zero substituted for the unrepresentable value,

though this might lead to a later divide by zero error which

cannot be so easily ignored.

(1997-08-25)