FSCALE can be used as an inverse to FXTRACT. Because FSCALE does not pop the exponent part, however, FSCALE must be followed by FSTP ST(1) in order to completely undo the effect of a preceding FXTRACT.
There is no limit on the range of the scale factor in ST(1). If the value is not integral, FSCALE uses the nearest integer smaller in magnitude; i.e., it chops the value toward 0. If the resulting integer is zero, the value in ST is not changed.