Mill Computing, Inc. Forums The Mill Architecture Posit math instead of IEEE FP?

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  • jpmhouston
    Participant
    Post count: 1
    #2783 |

    Interested in Mill insiders thoughts on “Posit” math, apparently John Gustafson’s third crack at a replacement for IEEE Floating Point, and the chances of being implemented in the Mill CPU. Would it make sense to be implemented as desired in only some concrete CPUs, or would it have to be in the spec across the whole family?

    John Gustafson presents: Beyond Floating Point – Next Generation Computer Arithmetic

    … patiently looking forward to more any juicy details about the Mill beyond the new years post, whether that be more videos or anything. (last year’s update vacuum after a semi-regular stream of videos had me wondering if a secretive company bought you guys up! admission: I daydream about Mill-powered Mac Pros)

  • Ivan Godard
    Keymaster
    Post count: 629

    Gustafson’s work is interesting but very controversial. I’m not enough of a floating point maven to comment on the mathematics of it. It seems clear that FP apps would need to be re-analyzed and most likely rewritten to take advantage of the format; the economics of that suggest very low and slow adoption rates, even with a hardware implementation available.

    However, the Mill is specification-driven. To add Gustafson-numbers (GNs) as a computation domain and their operation set is pretty trivial on the software side -a day or two to get the specification machinery to accept them and the tool chain to handle them and produce code. Then somebody has to figure out what a given operation on GNs actually does at the bit level and code that into the sim – maybe a week or two. Getting from there to gates is more, but not intolerably so. The biggest hassle would be getting them into clang/llvm as a recognized (and properly constant-folded and otherwise optimized) data type.

    Would GNs sell more Mills? Almost certainly not. However, certain very specialized needs might want GNs badly enough to NRE a machine with them. And if such a party cared about costs, we surely can produce a GN-supporting Mill a lot cheaper than they could be added to any other machine. Interested parties please apply here 🙂

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