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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: "A diagram of C23 basic types"
Date: Wed, 16 Apr 2025 16:11:01 -0700
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BGB <cr88192@gmail.com> writes:
> On 4/16/2025 3:04 PM, Scott Lurndal wrote:
>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>> candycanearter07 <candycanearter07@candycanearter07.nomail.afraid>
>>> writes:
[...]
>>>> Datetime is a nightmare, this is why we use a simple seconds-since-X
>>>> system.
>>>
>>> Indeed.  That makes it a slightly less unpleasant nightmare.
>> Back in the mainframe days, it was common to use julian dates
>> as they were both concise (5 BCD digits/20 bits) and sortable.
>>    YYDDD
>> If time was neeeded, it was seconds since midnight in a reference
>> timezone.
>
> One shorthand is to assume a year is 365.25 days (31557600 seconds),
> and then base everything else off this (initially ignoring things like
> leap-years, etc, just assume that the number of days per year is
> fractional).
>
> Then, say, 2629800 seconds per month, ...

So, a month is 30 days, 26 hours, and 15 minutes.  How is that useful?

> For some other calculations, one can assume an integer number of days
> (365), just that each day is 0.07% longer.
>
> For date/time calculations, one could then "guess" the date, and
> jitter it back/forth as needed until it was consistent with the
> calendar math.
>
> Estimate and subtract the year, estimate and subtract the month, then
> the day. Then if we have landed on the wrong day, adjust until it
> fits.
>
> Not really sure if there was a more standard way to do this.

Keeping track of time in a manner that's entirely consistent with
the Gregorian calendar is a solved problem.  C's standard library
has functions that will do that for you.  What is the point of
inventing a new and less accurate approximation?

[...]

> As for time since epoch:
> Microseconds (in a power-of-10 sense) are more common...

The C standard library already has "struct timespec", which represents
time with nanosecond precision.  Why invent something new with poorer
precision?

[...]

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */