If the destination is single- or double-real, the significand is rounded to the width of the destination according to the RC field of the control word, and the exponent is converted to the width and bias of the destination format. The over/underflow condition is checked for as well.
If ST contains zero, ±∞, or a NaN, then the significand is not rounded, but chopped (on the right) to fit the destination. Nor is the exponent converted; it too is chopped on the right. These operations preserve the value's identity as ∞ or NaN (exponent all ones).
The invalid-operation exception is not raised when the destination is a nonempty stack element.
A denormal operand in ST(0) causes an underflow. No denormal operand exception is raised.