I can now explain the microcode for an instruction called FSCALE that scales a number by a power of 2. It sounds simple, but the 8087 has an appalling number of special cases: positive and negative 0, two infinities, four rounding modes, three number sizes, six exceptions... so the code is complex.
The 8087's microcode is too complicated and low-level to explain here. For details, see my latest article:
https://www.righto.com/2026/09/8087-microcode-reverse-engineering-fscale.html
Credits: I've been working on this with the members of the "Opcode Collective", especially Smartest Blob and @gloriouscow, who converted the ROM images to microcode data and extensively analyzed the contents.
7/7
At the time, this bad boy would cost nearly $600 in today's money. Which is sadly in line with a baller PC upgrade in 2026