A.5.87 FISUB: Floating-Point/Integer Subtraction
FISUB mem16 ; DE /4 [8086,FPU]
FISUB mem32 ; DA /4 [8086,FPU]
FISUBR mem16 ; DE /5 [8086,FPU]
FISUBR mem32 ; DA /5 [8086,FPU]
FISUB subtracts the 16-bit or 32-bit integer stored in the given memory
location from ST0, and stores the result in ST0. FISUBR does the
subtraction the other way round, i.e. it subtracts ST0 from the given
integer, but still stores the result in ST0.