[Libguestfs] [PATCH nbdkit v2 1/6] Add new public nbdkit_parse_probability function

[Laszlo Ersek]

On 5/17/23 23:05, Eric Blake wrote:

> [Side note: if you really want a trip, read the 2023 SIGBOVIK article
> on "GradIEEEnt half decent" about 16-bit floating point values being
> exploited for their non-linear rounding properties as a way to create
> non-monotonic functions that can in turn form the basis of a Turing
> complete system capable of running a 36-second solution of Mario level
> 1-1 in 19k minutes of wall time using only half-precision
> floating-point operations... https://sigbovik.org/2023/,
> http://tom7.org/grad/murphy2023grad.pdf]

I've read the first few pages of this paper. It's amazing how capable
and dedicated the author is! (And I love his humor!)

Anyway: one of the footnotes says,

    There is seldom reason to change the rounding mode, and since it is
    a stateful act, you’re asking for it if you do. But the round-to-
    negative-infinity and round-to-positive-infinity modes are are
    useful for interval arithmetic, which is arguably the only truly
    reasonable way to use floating point. What you do is represent
    numbers as intervals (low and high endpoints) that contain the true
    value, and then perform each calculation on both endpoints. For
    computations on the low endpoint, you round down, and symmetrically
    for the high endpoint. This way, the true value is always within the
    interval, and you also know how much inaccuracy you have
    accumulated!

This echoes my earlier encounters with "interval arithmetic", and only
strengthens my aversion towards floating point in the present context.

Please proceed with collaborating on this series, I need to withdraw
from it.

Laszlo