I’ve had nights like that.

What WIN87EM.DLL Does

The IRQ 13 handler in WIN87EM.DLL performs the following steps:

• Disable interrupts (CLI)
• PUSH and POP the AX register 70 times, maybe it will slow things down
• Write zero to I/O port F0h to clear the PC/AT FPU error latch
• Mask a selection of interrupts
• Write an EOI to the master interrupt controller (but not slave)
• Execute the FNSTSW instruction to store the FPU status word (but only that)
• PUSH and POP the AX register 16 times, because speed kills
• Write zero to I/O port F0h again, in case it didn’t work the first time
• Execute the FNCLEX instruction to clear pending FPU exceptions
• Write zero to I/O port F0h again, because third time’s the charm
• PUSH and POP the AX register 16 times, because it was so much fun last time
• Execute the FNCLEX instruction again, just to be really sure
• PUSH and POP the AX register 16 times, because it’s the thing to do
• Write zero to I/O port F0h again, because three times might not have been enough
• Finally jump to code that doesn’t look crazy

Wow.