From: Richard Henderson <richard.henderson@linaro.org>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-devel@nongnu.org, "Alex Bennée" <alex.bennee@linaro.org>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Eduardo Habkost" <eduardo@habkost.net>,
"Laurent Vivier" <laurent@vivier.eu>
Subject: Re: [PATCH 06/10] fpu: Move m68k_denormal fmt flag into floatx80_behaviour
Date: Thu, 20 Feb 2025 10:39:49 -0800 [thread overview]
Message-ID: <d7a0260d-5cdb-4e87-b12c-32e1dee4df1c@linaro.org> (raw)
In-Reply-To: <CAFEAcA_upC=ty1PWXOSsHHgk67EoPi6rB2DhK2M5_q2mzUCW=Q@mail.gmail.com>
On 2/20/25 09:12, Peter Maydell wrote:
> That suggests that we are correctly implementing the x87
> required behaviour in QEMU, and so that the TODO comment
> I add in this patch isn't right. But then I'm a bit confused
> about what the code is actually doing. Why do we need to look
> at fmt->m68k_denormal in the input (canonicalize) code (i.e.
> to have different behaviour here for x86 and m68k), if
> both x86 and m68k accept these pseudodenormals as input?
>
> Is the difference that for x86 we accept but canonicalize
> into the equivalent normal number immediately on input,
> whereas for m68k we accept and leave the pseudodenormal
> as a pseudodenormal (well, m68k calls these a kind of
> normal number) ?
The difference is in interpretation: x86 ignores the explicit integer bit of the
pseudo-denormal, m68k considers it part of the input value. This gives m68k one extra bit
of range in their denormal, which allows representation of smaller numbers.
r~
next prev parent reply other threads:[~2025-02-20 18:40 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-02-17 12:50 [PATCH 00/10] fpu: Remove remaining target ifdefs and build only once Peter Maydell
2025-02-17 12:50 ` [PATCH 01/10] fpu: Make targets specify floatx80 default Inf at runtime Peter Maydell
2025-02-17 18:09 ` Richard Henderson
2025-02-21 14:42 ` Philippe Mathieu-Daudé
2025-02-21 15:16 ` Peter Maydell
2025-02-17 12:50 ` [PATCH 02/10] target/m68k: Avoid using floatx80_infinity global const Peter Maydell
2025-02-17 18:10 ` Richard Henderson
2025-02-21 13:51 ` Philippe Mathieu-Daudé
2025-02-17 12:50 ` [PATCH 03/10] target/i386: " Peter Maydell
2025-02-17 18:10 ` Richard Henderson
2025-02-21 13:40 ` Philippe Mathieu-Daudé
2025-02-17 12:50 ` [PATCH 04/10] fpu: Make targets specify whether floatx80 Inf can have Int bit clear Peter Maydell
2025-02-17 18:13 ` Richard Henderson
2025-02-21 13:12 ` Philippe Mathieu-Daudé
2025-02-17 12:50 ` [PATCH 05/10] fpu: Make floatx80 invalid encoding settable at runtime Peter Maydell
2025-02-17 18:45 ` Richard Henderson
2025-02-21 13:14 ` Philippe Mathieu-Daudé
2025-02-17 12:50 ` [PATCH 06/10] fpu: Move m68k_denormal fmt flag into floatx80_behaviour Peter Maydell
2025-02-17 19:14 ` Richard Henderson
2025-02-20 17:12 ` Peter Maydell
2025-02-20 18:39 ` Richard Henderson [this message]
2025-02-20 18:54 ` Peter Maydell
2025-02-21 14:14 ` Philippe Mathieu-Daudé
2025-02-21 22:24 ` Richard Henderson
2025-02-17 12:50 ` [PATCH 07/10] fpu: Always decide no_signaling_nans() at runtime Peter Maydell
2025-02-17 13:13 ` Philippe Mathieu-Daudé
2025-02-17 19:25 ` Richard Henderson
2025-02-17 12:50 ` [PATCH 08/10] fpu: Always decide snan_bit_is_one() " Peter Maydell
2025-02-17 13:15 ` Philippe Mathieu-Daudé
2025-02-17 19:26 ` Richard Henderson
2025-02-17 12:50 ` [PATCH 09/10] fpu: Don't compile-time disable hardfloat for PPC targets Peter Maydell
2025-02-17 19:27 ` Richard Henderson
2025-02-17 12:50 ` [PATCH 10/10] fpu: Build only once Peter Maydell
2025-02-17 19:28 ` Richard Henderson
2025-02-20 8:48 ` [PATCH 00/10] fpu: Remove remaining target ifdefs and build " Philippe Mathieu-Daudé
2025-02-20 9:00 ` Philippe Mathieu-Daudé
2025-02-21 10:48 ` Philippe Mathieu-Daudé
2025-02-21 13:05 ` Philippe Mathieu-Daudé
2025-02-21 13:28 ` Peter Maydell
2025-02-21 13:48 ` Philippe Mathieu-Daudé
2025-02-21 14:41 ` Philippe Mathieu-Daudé
2025-02-21 15:19 ` Peter Maydell
2025-02-21 16:21 ` Philippe Mathieu-Daudé
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