Highly Divergent Profiles: For routing configurations that are not pre-calculated as common scenarios and whose costs vary too much from default configurations, the original A* algorithm might still be faster (and is often used as an automatic fallback).
Real-mode programs freely execute CLI and STI to control interrupts, PUSHF and POPF to manipulate flags, INT n for DOS and BIOS calls, and IN/OUT for hardware I/O. In normal protected mode, these instructions are privilege-checked -- they execute normally if the caller has sufficient privilege, and fault otherwise. The 386 can't simply let V86 tasks execute them freely -- a DOS program disabling interrupts would bring down the whole system -- but trapping on every INT 21h call would make V86 impractically slow.
，这一点在搜狗输入法下载中也有详细论述
Original OSM: ~2.07 billion points, ~2.42 billion edges
"Of course, there were no women astronauts back then. But I just thought, I'll be a lady astronaut."