Re: On disable_cost

On Tue, 2019-12-10 at 15:50 -0700, Jim Finnerty wrote:
> As a proof of concept, I hacked around a bit today to re-purpose one of the
> bits of the Cost structure to mean "is_disabled" so that we can distinguish
> 'disabled' from 'non-disabled' paths without making the Cost structure any
> bigger. In fact, it's still a valid double. The obvious choice would have
> been to re-purpose the sign bit, but I've had occasion to exploit negative
> costs before so for this POC I used the high-order bit of the fractional
> bits of the double. (see Wikipedia for double precision floating point for
> the layout).
>
> The idea is to set a special bit when disable_cost is added to a cost.
> Dedicating multiple bits instead of just 1 would be easily done, but as it
> is we can accumulate many disable_costs without overflowing, so just
> comparing the cost suffices.

Doesn't that rely on a specific implementation of double precision (IEEE)?
I thought that we don't want to limit ourselves to platforms with IEEE floats.

Yours,
Laurenz Albe