Arithmetic underflow

The term arithmetic underflow (also floating-point underflow, or just underflow) is a condition in a computer program where the result of a calculation is a number of more precise absolute value than the computer can actually represent in memory on its central processing unit (CPU).

Arithmetic underflow can occur when the true result of a floating-point operation is smaller in magnitude (that is, closer to zero) than the smallest value representable as a normal floating-point number in the target datatype. Underflow can in part be regarded as negative overflow of the exponent of the floating-point value. For example, if the exponent part can represent values from 128 to 127, then a result with a value less than 128 may cause underflow.