NASM 2.05 based x86 Instruction Reference[ch091]

A.5.71 FCLEX, FNCLEX: Clear Floating-Point Exceptions FCLEX ; 9B DB E2 [8086,FPU] FNCLEX ; DB E2 [8086,FPU] FCLEX clears any floating-point exceptions which may be pending. FNCLEX does the same thing but doesn't wait for previous floating-point operations (including the _handling_ of pending exceptions) to finish first.