## ALP Programming Guide and Reference

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### Notes

FSTSW checks for unmasked floating-point error conditions before storing the status word; FNSTSW does not.

FSTSW and FNSTSW are used primarily in conditional branching (after a comparison, FPREM, FPREM1, or FXAM instruction). They can also be used to invoke exception handlers (by polling the exception bits) in environments that do not use interrupts.

When FNSTSW AX is run, the AX register is updated before the processor runs any further instructions. The status stored is that from the completion of the prior ESC instruction.