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Message-ID: <4310373-42d-9611-639-e5e462f22ef@redhat.com>
Date: Thu, 25 Jul 2024 14:57:42 +0000 (UTC)
From: Joseph Myers <josmyers@...hat.com>
To: libc-coord@...ts.openwall.com
Subject: Re: #pragma STDC FENV_ACCESS ON
On Thu, 25 Jul 2024, enh wrote:
> btw, see also https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2746r0.pdf
> where the guy down the hall is suggesting that rather than copy
> FENV_ACCESS into C++, C++ should just say "the <fenv.h> rounding mode
> stuff is too broken --- let's replace it with _types_ that carry a
> rounding mode".
Rounding modes are logically a property of operations, not types (and in
particular, for interval arithmetic you may want to do operations on the
same value but with different rounding modes). The FENV_ROUND pragma (in
TS 18661-1 / C23), assigning a constant rounding direction to a region of
source code, is better fitted to practical uses of rounding modes than
dynamic rounding modes are (it's unfortunate that IEEE 754-1985 was rather
influential in processors tending to support dynamic and not constant
modes).
--
Joseph S. Myers
josmyers@...hat.com
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