Re: [PATCH 4/5] tm.3type: describe tm_zone, tm_gmtoff

["G. Branden Robinson" <g.branden.robinson@gmail.com>]

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Hi Alex,

At 2025-10-29T11:21:27+0100, Alejandro Colomar wrote:
> On Wed, Oct 29, 2025 at 04:07:18AM -0500, G. Branden Robinson wrote:
> > At 2022-07-19T14:17:15+0200, Alejandro Colomar wrote:
> > > Could you come up with a more mathematically precise term for
> > > "reverse"?  What is reverse?  The additive inverse?  Maybe use
> > > "additive inverse"?  I think "opposite" also has the meaning of
> > > additive inverse in maths, and it's maybe a simpler term (although
> > > additive inverse is more precise, IMHO).  But reverse is
> > > definitely confusing to me.
> > 
> > I think the idiomatic term is "inverse".
> 
> Inverse is too generic.  Inverse functions do something else.  The
> specific terms are "opposite (of a) number" and "additive inverse",
> AFAIK, and maybe also "inverse (of a) number".

Yes, but `tm_gmtoff` and `timezone` are _scalars_, not functions.

tzset(3):
     extern long timezone;

tm(3type):
     struct tm {
...
         /* Since POSIX.1‐2024:  */
         long        tm_gmtoff; /* Seconds East of UTC */
...
}

Consequently, if they possess an inversional relationship at all, they
must be either additive or multiplicative inverses of the other,[1] and
the page now makes it clear which.

tm(3type):
     tm_gmtoff is the difference, in seconds, of the timezone
     represented by this broken‐down time and UTC (this is the additive
     inverse of timezone(3)).

I apologize for re-raising an old and as far as I can tell,
satisfactorily settled issue.  I was looking at messages in neomutt with
a non-obvious filter in place (meaning one I'd applied, wandered away
from the computer, and forgot about), and since your message of 19 July
was still in my inbox, I got confused and thought it was an item still
solicting my input.

Regards,
Branden

[1] If there's another kind of inverse that can apply over the integers,
    I don't know what it is.

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