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From: Paul Clarke <pc@us.ibm.com>
To: qemu-devel@nongnu.org
Subject: [Qemu-devel] [Bug 1841491] Re: floating point emulation can fail to set FE_UNDERFLOW
Date: Tue, 27 Aug 2019 04:08:07 -0000	[thread overview]
Message-ID: <156687888782.6965.1367413426931573379.malone@gac.canonical.com> (raw)
In-Reply-To: 156686849716.6431.16425651381928336460.malonedeb@gac.canonical.com

** Attachment added: "2nd file of float testcase"
   https://bugs.launchpad.net/qemu/+bug/1841491/+attachment/5284821/+files/ffma.c

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https://bugs.launchpad.net/bugs/1841491

Title:
  floating point emulation can fail to set FE_UNDERFLOW

Status in QEMU:
  New

Bug description:
  Floating point emulation can fail to set FE_UNDERFLOW in some
  circumstances. This shows up often in glibc's "math" tests. A similar
  test is attached.

  This is similar to bug #1841442, but not the same problem, and I don't
  think the fix will be in the same code.

  On ppc64le native:
  --
  $ gcc -c -O2 fma.c
  $ gcc -O2 test-fma.c fma.o -lm -o test-fma
  $ ./test-fma $(./test-fma)
  fma(0x1.ffffffffffffcp-1022, 0x1.0000000000001p-1, 0x0.0000000000001p-1022)
  0x0

  0xa000000
  FE_INEXACT FE_UNDERFLOW 
  0x1p-1022
  --

  On qemu-system-ppc64:
  --
  $ ./test-fma $(./test-fma)
  fma(0x1.ffffffffffffcp-1022, 0x1.0000000000001p-1, 0x0.0000000000001p-1022)
  0x0

  0x2000000
  FE_INEXACT 
  0x1p-1022
  --

  QEMU versions vary, but not too much, and are pretty close to git HEAD:
  - 586f3dced9 (HEAD -> master, origin/master, origin/HEAD) Merge remote-tracking branch 'remotes/cohuck/tags/s390x-20190822' into staging
  - 864ab31 Update version for v4.1.0-rc4 release

  There are worse symptoms on qemu-x86_64, but this is apparently not
  surprising per
  https://bugs.launchpad.net/qemu/+bug/1841442/comments/6.

To manage notifications about this bug go to:
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  parent reply	other threads:[~2019-08-27  4:16 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-27  1:14 [Qemu-devel] [Bug 1841491] [NEW] floating point emulation can fail to set FE_UNDERFLOW Paul Clarke
2019-08-27  1:16 ` [Qemu-devel] [Bug 1841491] " Paul Clarke
2019-08-27  4:06 ` Paul Clarke
2019-08-27  4:08 ` Paul Clarke [this message]
2019-08-27  4:29 ` Richard Henderson
2020-01-09 13:32 ` Thomas Huth
2020-01-09 15:24 ` Paul Clarke
2020-01-10  8:38 ` Thomas Huth

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