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From: Eduardo Habkost <ehabkost@redhat.com>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: "Greg Kurz" <groug@kaod.org>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	"Luis Pires" <luis.pires@eldorado.org.br>,
	qemu-ppc@nongnu.org, "David Gibson" <david@gibson.dropbear.id.au>,
	"Philippe Mathieu-Daudé" <f4bug@amsat.org>
Subject: Re: [PATCH v3 03/22] host-utils: introduce uabs64()
Date: Thu, 21 Oct 2021 18:34:42 -0400	[thread overview]
Message-ID: <CAOpTY_r21YorsZVWyV8D7yOD-wXvNfhj-i9YO2VKgLWjq=_jbg@mail.gmail.com> (raw)
In-Reply-To: <e324a9af-daab-273b-e448-33386c79e4e6@linaro.org>

On Thu, Oct 21, 2021 at 4:04 PM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 9/10/21 4:26 AM, Luis Pires wrote:
> > Introduce uabs64(), a function that returns the absolute value of
> > a 64-bit int as an unsigned value. This avoids the undefined behavior
> > for common abs implementations, where abs of the most negative value is
> > undefined.
>
> I do question the comment there wrt undefined. We compile with -fwrapv, which means that
> *no* overflow is undefined; we always have properly truncated twos-compliment values.

Can we really assume that -fwrapv would make llabs(LLONG_MIN) not
undefined? We would be calling a function compiled by somebody else
(possibly without -fwrapv).

--
Eduardo



  reply	other threads:[~2021-10-21 22:40 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10 11:26 [PATCH v3 00/22] target/ppc: DFP instructions using decodetree Luis Pires
2021-09-10 11:26 ` [PATCH v3 01/22] host-utils: Fix overflow detection in divu128() Luis Pires
2021-09-10 11:26 ` [PATCH v3 02/22] host-utils: fix missing zero-extension in divs128 Luis Pires
2021-10-21 20:02   ` Richard Henderson
2021-09-10 11:26 ` [PATCH v3 03/22] host-utils: introduce uabs64() Luis Pires
2021-10-21 20:04   ` Richard Henderson
2021-10-21 22:34     ` Eduardo Habkost [this message]
2021-10-21 23:23       ` Richard Henderson
2021-09-10 11:26 ` [PATCH v3 04/22] i386/kvm: Replace abs64() with uabs64() from host-utils Luis Pires
2021-09-10 11:26 ` [PATCH v3 05/22] host-utils: move checks out of divu128/divs128 Luis Pires
2021-10-21 20:11   ` Richard Henderson
2021-09-10 11:26 ` [PATCH v3 06/22] host-utils: move udiv_qrnnd() to host-utils Luis Pires
2021-10-21 20:14   ` Richard Henderson
2021-09-10 11:26 ` [PATCH v3 07/22] host-utils: add 128-bit quotient support to divu128/divs128 Luis Pires
2021-10-21 21:14   ` Richard Henderson
2021-10-25 18:51     ` Luis Fernando Fujita Pires
2021-09-10 11:26 ` [PATCH v3 08/22] host-utils: add unit tests for divu128/divs128 Luis Pires
2021-10-21 21:16   ` Richard Henderson
2021-09-10 11:26 ` [PATCH v3 09/22] libdecnumber: introduce decNumberFrom[U]Int128 Luis Pires
2021-09-10 11:26 ` [PATCH v3 10/22] target/ppc: Move REQUIRE_ALTIVEC/VECTOR to translate.c Luis Pires
2021-09-10 11:26 ` [PATCH v3 11/22] target/ppc: Introduce REQUIRE_FPU Luis Pires
2021-09-10 11:26 ` [PATCH v3 12/22] target/ppc: Implement DCFFIXQQ Luis Pires
2021-10-21 21:27   ` Richard Henderson
2021-09-10 11:26 ` [PATCH v3 13/22] host-utils: Introduce mulu128 Luis Pires
2021-09-10 11:26 ` [PATCH v3 14/22] libdecnumber: Introduce decNumberIntegralToInt128 Luis Pires
2021-09-10 11:26 ` [PATCH v3 15/22] target/ppc: Implement DCTFIXQQ Luis Pires
2021-10-21 21:39   ` Richard Henderson
2021-10-25 18:51     ` Luis Fernando Fujita Pires
2021-09-10 11:26 ` [PATCH v3 16/22] target/ppc: Move dtstdc[q]/dtstdg[q] to decodetree Luis Pires
2021-10-21 21:58   ` Richard Henderson
2021-10-25 18:52     ` Luis Fernando Fujita Pires
2021-09-10 11:26 ` [PATCH v3 17/22] target/ppc: Move d{add, sub, mul, div, iex}[q] " Luis Pires
2021-10-21 22:05   ` [PATCH v3 17/22] target/ppc: Move d{add,sub,mul,div,iex}[q] " Richard Henderson
2021-09-10 11:26 ` [PATCH v3 18/22] target/ppc: Move dcmp{u, o}[q], dts{tex, tsf, tsfi}[q] " Luis Pires
2021-10-21 22:15   ` [PATCH v3 18/22] target/ppc: Move dcmp{u,o}[q],dts{tex,tsf,tsfi}[q] " Richard Henderson
2021-09-10 11:26 ` [PATCH v3 19/22] target/ppc: Move dquai[q], drint{x, n}[q] " Luis Pires
2021-10-21 22:22   ` [PATCH v3 19/22] target/ppc: Move dquai[q], drint{x,n}[q] " Richard Henderson
2021-09-10 11:26 ` [PATCH v3 20/22] target/ppc: Move dqua[q], drrnd[q] " Luis Pires
2021-10-21 22:27   ` Richard Henderson
2021-09-10 11:26 ` [PATCH v3 21/22] target/ppc: Move dct{dp, qpq}, dr{sp, dpq}, dc{f, t}fix[q], dxex[q] " Luis Pires
2021-10-21 22:35   ` [PATCH v3 21/22] target/ppc: Move dct{dp,qpq},dr{sp,dpq},dc{f,t}fix[q],dxex[q] " Richard Henderson
2021-09-10 11:26 ` [PATCH v3 22/22] target/ppc: Move ddedpd[q], denbcd[q], dscli[q], dscri[q] " Luis Pires
2021-10-21 23:21   ` [PATCH v3 22/22] target/ppc: Move ddedpd[q],denbcd[q],dscli[q],dscri[q] " Richard Henderson
2021-09-15  3:15 ` [PATCH v3 00/22] target/ppc: DFP instructions using decodetree David Gibson
2021-09-20 18:50 ` Luis Fernando Fujita Pires
2021-10-14 17:02   ` Luis Fernando Fujita Pires
2021-10-15  3:15     ` david
2021-10-15 11:52       ` Luis Fernando Fujita Pires

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