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Re: Floating-point constant folding in Emacs byte compiler
From: |
Pip Cet |
Subject: |
Re: Floating-point constant folding in Emacs byte compiler |
Date: |
Fri, 23 Mar 2018 20:52:52 +0000 |
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)
- Floating-point constant folding in Emacs byte compiler, Paul Eggert, 2018/03/22
- Re: Floating-point constant folding in Emacs byte compiler,
Pip Cet <=
- Re: Floating-point constant folding in Emacs byte compiler, Eli Zaretskii, 2018/03/24
- Re: Floating-point constant folding in Emacs byte compiler, Robert Pluim, 2018/03/26
- Re: Floating-point constant folding in Emacs byte compiler, Eli Zaretskii, 2018/03/26
- Re: Floating-point constant folding in Emacs byte compiler, Robert Pluim, 2018/03/26
- Re: Floating-point constant folding in Emacs byte compiler, Eli Zaretskii, 2018/03/26
- Re: Floating-point constant folding in Emacs byte compiler, Pip Cet, 2018/03/26
- Re: Floating-point constant folding in Emacs byte compiler, Eli Zaretskii, 2018/03/26
- Re: Floating-point constant folding in Emacs byte compiler, Paul Eggert, 2018/03/26
- Re: Floating-point constant folding in Emacs byte compiler, Paul Eggert, 2018/03/27
- Re: Floating-point constant folding in Emacs byte compiler, Pip Cet, 2018/03/30