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kens 1 hours ago [-]
Author here if anyone has questions about the 8087's microcode...
ChuckMcM 31 minutes ago [-]
I worked in Systems Validation at Intel when the 8087 was current. Intel had an engineer dedicated to validating customer bug reports and reproducing them. Day in, day out, that's pretty much all he did. Sooooo many corner cases, and so many opinions on what the 'right' thing to do was when you lost precision[1].
[1] I'd say that over half of the bug reports were people who were annoyed that doing fp instructions in one order got them the right answer but in another order got them the wrong answer.
mysterydip 55 minutes ago [-]
80 bits always seemed a strange choice for floating point, but as soon as you said there’s a 16-bit exponent and a 64-bit fraction part, it made sense.
I assume microcode was a choice for both ease of development/testing/changes and saving die space. Would there come a point later on where performance could be gained by converting the microcode into a full set of discrete logic, or is that not worth the effort?
mysterion1 38 minutes ago [-]
Wouldn't it be simpler for Intel to have designed a chip, with those 8 identical instructions (xfer, shift, add, arith, far jmp, far call, local jmp, misc), but read/executed from normal RAM accessible by the user, perhaps with a tiny cache, instead all these ROM/microcode special compression/hidden architecture shenanigans?
russdill 24 minutes ago [-]
You're them moving and storing a lot of repetitive instruction data.
[1] I'd say that over half of the bug reports were people who were annoyed that doing fp instructions in one order got them the right answer but in another order got them the wrong answer.
I assume microcode was a choice for both ease of development/testing/changes and saving die space. Would there come a point later on where performance could be gained by converting the microcode into a full set of discrete logic, or is that not worth the effort?