A.5.109 FXAM: Examine Class of Value in ST0
FXAM ; D9 E5 [8086,FPU]
FXAM sets the FPU flags C3, C2 and C0 depending on the type of value
stored in ST0:
Register contents Flags
Unsupported format 000
NaN 001
Finite number 010
Infinity 011
Zero 100
Empty register 101
Denormal 110
Additionally, the C1 flag is set to the sign of the number.