Die analysis of the 8087 math coprocessor's fast bit shifter (2020) (righto.com)
38 points by Jimmc414 4 hours ago
tasty_freeze 2 hours ago
Northstar made an S-100 card which did FP math, using BCD arithmetic. It had a ucode ROM and a 4b (single digit) ALU, and a few small RAMs to hold the digits. If I remember correctly you could program it to select how many digits you wanted in your representation, up to 14 digits. It did everything one digit at a time, and it had a 256 byte ROM to carry out any digit*digit product in one cycle. For normalization no data was moved -- just the pointer to the appropriate digit was incremented or decremented.
https://s100computers.com/Hardware%20Folder/NorthStar/FP%20B...
trollbridge 2 hours ago
Must…resist…clicking link… I’ve got a lot to today and this is like carefully crafted bait to tie me up for the next 4 hours. :-)
bell-cot 4 hours ago
Closely related, 8 days ago, 138 points & 28 comments:
https://news.ycombinator.com/item?id=48519011 (about the 8087's adder)
Jimmc414 3 hours ago
That's a different article by the same author, Ken Shirriff
https://www.righto.com/2020/05/die-analysis-of-8087-math-cop...
https://www.righto.com/2026/06/intel-8087-adder-reverse-engi...
bell-cot 2 hours ago
Yes - I was just trying to give things a "this is interesting, so upvote & discuss!" kick. In the absence of Ken popping up with good "Author here for your 8087 questions" comment.