[PATCH] MOD of oxygen at pO2 of 1.6 is 20ft

[Dirk Hohndel]

On Sun, Jul 05, 2015 at 12:11:15PM -0700, Linus Torvalds wrote:
> On Sun, Jul 5, 2015 at 11:56 AM, Dirk Hohndel <dirk at hohndel.org> wrote:
> > static inline depth_t gas_mod(struct gasmix *mix, pressure_t po2_limit, int roundto) {
> >         depth_t depth;
> >         depth.mm = ((po2_limit.mbar * 1000 / get_o2(mix) * 10 - 10000) / roundto) * roundto;
> >         return depth;
> > }
> >
> > So all we need to do is adjust this function to add (roundto - 1) to the
> > enumerator before deviding by roundto, correct?
> 
> Ugh. I think it would be better to write it more readably first.
> That's a particularly unreadable line of noise.

Well, Robert wrote it, now he can fix it.

> At the very least, split it up, and do the rounding separately. And
> no, you shouldn't add "roundto-1" unless you always want to round
> _up_. I'd assume you'd want to round-to-nearest, and add "roundto/2"
> instead.

Umm. Err. Yeah. That's what I meant to say...

> Or just use floating point and "rint()".
> 
> So something like
> 
>      depth.mm = po2_limit.mbar * 1000 / get_o2(mix) * 10 - 10000;
>      depth.mm = rint(depth.mm / (double) roundto) * roundto;

That ceratinly would be much more readable.

> Which just leaves the initial actual depth math, which is also qutie
> debatably wrong.
> 
> Looking at that first line, it truncates the depth to cm because it
> does that "*10" last, after having done a truncating divide. So it
> does the math in steps of 10mm, which looks bogus too. Of course, that
> math is just hardcoding the "one bar per 10m of water", which might be
> a bit questionable to begin with. But I guess that's how people
> calculate PO2 limits, so..

And of course you could just send a patch... you used to do that  :-)

/D