Feels like an honor to be able to ask. I've appreciated your work for a few years now especially on the Apollo gear restoration.
Anyway, question on the ones you thought were wrong (I think "just" the trig functions). Is there a running system you can use that can be used to confirm your findings? Especially considering your previous post on the pentium division bug, maybe they got this wrong too?
A running system won't really help me since I'm sure it will give the right answer. I need to know what's happening internally, which remains hidden in a running processor.
My guess is that it made things both easier and harder. Harder in the sense that you couldn't just throw together floating point circuits; you had to deal with lots of special cases. But easier in the sense that the tricky design decisions were already made for you. And easier to test against a known standard.
Are you working your way up through the eras of CPU's? How far do you predict you'll be able to get? (Ps. Thanks for all the awesome insight you've shared)
It's sort of random. My intent is to focus on the 8086, but someone asked about the 386 so I looked at that a bit. Then I saw the Navajo Pentium rug in a museum so I figured I should look at a real Pentium to compare. And then I wondered if I could find the FDIV bug. So one thing leads to another. I don't think I'll be able to go much beyond the Pentium with an optical microscope, though.
Do I understand it right that excluding the two metal layers, there's only a single "layer" of "logic" inside? I reckon newer CPUs have multiple, making imaging based reversing more difficult?
Even modern chips have a single layer of transistors, although there is research into 3D transistor stacking. (Flash memory stacks dies for more density.) Modern CPUs have much, much smaller transistors as well as constructing them more vertically (FinFET) but it is still a single layer. Modern processors can have over a dozen layers of metal, while the Pentium I examined has just 3 metal layers. I'm not going to be reverse-engineering a modern chip since you need an electron microscope to see the features; the features are orders of magnitude smaller than the wavelength of light.
Anyway, question on the ones you thought were wrong (I think "just" the trig functions). Is there a running system you can use that can be used to confirm your findings? Especially considering your previous post on the pentium division bug, maybe they got this wrong too?