From: Pip Cet <pipcet@gmail.com>
To: Paul Eggert <eggert@cs.ucla.edu>
Cc: Emacs development discussions <emacs-devel@gnu.org>
Subject: Re: Floating-point constant folding in Emacs byte compiler
Date: Fri, 23 Mar 2018 20:52:52 +0000 [thread overview]
Message-ID: <CAOqdjBdWdq32C1r8qzguSWmr1_cVAShZcPMnRgmi4vQX6j3R-w@mail.gmail.com> (raw)
In-Reply-To: <2ce39e5c-cd1b-65d6-b125-719caad67932@cs.ucla.edu>
Is this really specific to floating-point expressions, though?
(byte-compile (lambda (x) (* #x10000 #x10000 #x10000 #x10000)))
#[(x) "À\207" [0] 1]
(at least on this somewhat oudated version of Emacs). Note the 0 in
the constant vector, which hardcodes the <65-bit-ness of fixnums.
I imagine that on a 32-bit version of emacs, (byte-compile (lambda (x)
(* #x10000 #x10000))) similarly produces a constant-zero function,
which will produce the wrong result when fixnums are actually 62 bits
long.
(This is tangential, but I think that it might make sense, at some
point in the future, to switch to JavaScript-like
everything-is-a-float-but-there's-just-one-NaN "numbers"; that would
be quite a bit of work already, since several functions do different
things for integer and float arguments (I feel they should be fixed
anyway), and it would be nice to be able to point to the current
byte-opt situation as evidence that if you're relying on unusual
number behavior, you're already doing something wrong)
next prev parent reply other threads:[~2018-03-23 20:52 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-22 23:04 Floating-point constant folding in Emacs byte compiler Paul Eggert
2018-03-23 1:26 ` Stefan Monnier
2018-03-23 5:22 ` Paul Eggert
2018-03-23 8:24 ` Eli Zaretskii
2018-03-23 20:00 ` Paul Eggert
2018-03-23 8:15 ` Eli Zaretskii
2018-03-23 20:52 ` Pip Cet [this message]
2018-03-24 6:25 ` Eli Zaretskii
2018-03-26 9:39 ` Robert Pluim
2018-03-26 15:13 ` Eli Zaretskii
2018-03-26 15:57 ` Robert Pluim
2018-03-26 16:02 ` Eli Zaretskii
2018-03-26 18:23 ` Pip Cet
2018-03-26 18:29 ` Eli Zaretskii
2018-03-27 0:28 ` Paul Eggert
2018-03-27 23:28 ` Paul Eggert
2018-03-30 16:26 ` Pip Cet
2018-03-30 16:31 ` Noam Postavsky
2018-03-30 16:39 ` Paul Eggert
2018-04-02 10:56 ` Pip Cet
2018-04-02 11:22 ` Eli Zaretskii
2018-04-02 11:42 ` Pip Cet
2018-04-02 12:50 ` Eli Zaretskii
2018-04-02 14:50 ` Stefan Monnier
2018-04-02 15:02 ` Pip Cet
2018-04-02 12:57 ` Noam Postavsky
2018-04-02 13:30 ` Eli Zaretskii
2018-04-02 14:48 ` Stefan Monnier
2018-04-02 19:20 ` Paul Eggert
2018-04-02 19:39 ` Pip Cet
2018-04-02 19:58 ` Eli Zaretskii
2018-04-02 20:55 ` Pip Cet
[not found] ` <<83y3i568i0.fsf@gnu.org>
2018-04-02 13:37 ` Drew Adams
2018-04-02 14:05 ` Eli Zaretskii
2018-04-02 14:54 ` Pip Cet
2018-04-02 15:02 ` Drew Adams
2018-03-26 17:52 ` Stefan Monnier
2018-03-26 18:30 ` Eli Zaretskii
2018-03-27 0:08 ` Paul Eggert
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