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Re: Checking for loss of information on integer conversion
From: |
Eli Zaretskii |
Subject: |
Re: Checking for loss of information on integer conversion |
Date: |
Sun, 18 Feb 2018 22:24:34 +0200 |
> From: Paul Eggert <address@hidden>
> Cc: address@hidden, address@hidden
> Date: Sun, 18 Feb 2018 12:04:20 -0800
>
> > Emacs Lisp is not used to write software that controls
> > aircraft and spaceships
>
> Actually, I maintain Emacs Lisp code that controls timestamps used in
> aircraft
> and spaceships. I'm not saying that Emacs itself runs the aircraft and
> spaceships, but it definitely is used to develop software and data used
> there.
> As luck would have it, I'm currently engaged in an email thread about time
> transfer between Earth and Mars (yes, this is really a thing and people are
> trying to do it with millisecond precision) that is related to a project
> where I
> regularly use Emacs Lisp. See the thread containing this message:
Interesting, but not really relevant to the issue at hand, IMO. I was
talking about real-time control, not off-line calculations. And I did
propose to have this feature as opt-in, so the kind of calculations
that transfer me to Mars could still be held safely and accurately.
> > More generally, why signaling an error by default in this case is a
> > good idea? ... That would
> > be similar to behavior of equivalent constructs in C programs
>
> Sure, and C compilers typically issue diagnostics for situations similar to
> what's in Bug#30408. For example, for this C program:
>
> int a = 18446744073709553664;
>
> GCC issues a diagnostic, whereas for the similar Emacs Lisp program:
>
> (setq b 18446744073709553664)
>
> Emacs silently substitutes a number that is off by 2048.
I'm okay with flagging such constants during byte compilation. I was
talking only about run-time diagnostics, not compile-time diagnostics.
> When people write a floating-point number they naturally expect it to have
> some
> fuzz. But when they write an integer they expect it to be represented
> exactly,
> and not to be rounded.
That is true, but Emacs behaved like it does today for many years, and
I'm worried by the possible breakage such a significant behavior
change could have, including on our own code.
- Checking for loss of information on integer conversion, Paul Eggert, 2018/02/17
- Re: Checking for loss of information on integer conversion, Eli Zaretskii, 2018/02/18
- Re: Checking for loss of information on integer conversion, Juliusz Chroboczek, 2018/02/18
- Re: Checking for loss of information on integer conversion, Richard Stallman, 2018/02/19
- Re: Checking for loss of information on integer conversion, Juliusz Chroboczek, 2018/02/22
- Re: Checking for loss of information on integer conversion, Eli Zaretskii, 2018/02/22