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8087 Emulation on 8086 Systems

63 points by ingve

by wglb

0 subcomment

While I was at Mark Williams back in the day, the engineers wrote 8087 emulation floating point for the Mark Williams 8086 compiler. This involved some quality time with the Volume 2 of Knuth in the log division section.

by watersb

1 subcomments

> Because the 8086 had no facility for emulating an FPU (unlike the 80286 and later processors), the emulation mechanism was somewhat complex and required tight cooperation of assemblers/compilers, linkers, and run-time libraries.
The article goes into some detail on the extra effort required to implement FPU hardware emulation on a platform that did not especially support it.
Modern implementation of FPU emulation might be more straightforward.
I haven't worked with FPU emulation on microcontrollers, which is probably the most common use case these days.

by xattt

11 subcomments

The article states that the 8087 was an expensive add-on.
Was this price point a deliberate market differentiator, or was there some special sauce within FPU that was otherwise difficult to attain?

by bombcar

2 subcomments

The interesting thing about the 8087 is that the co-processor interface was kind of generic. In theory you could have had things beyond just an FPU, but I don't know if much was ever done using it.

by dehrmann

1 subcomments

by anthk

0 subcomment

https://github.com/howerj/muxleq (subleq and muxleq). Look at the EForth code on how a small FP it's implemented. Also, learn about Forth, it's dumb easy to understand.