[v1] Misc patches for 2020-06-24

[PULL 16/31] softfloat: fix floatx80 remainder pseudo-denormal check for zero

Paolo Bonzini posted 31 patches 5 years, 7 months ago

Diff against v2
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Maintainers: Gerd Hoffmann <kraxel@redhat.com>, Igor Mammedov <imammedo@redhat.com>, "Alex Bennée" <alex.bennee@linaro.org>, Laurent Vivier <lvivier@redhat.com>, Peter Maydell <peter.maydell@linaro.org>, Eduardo Habkost <ehabkost@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, Richard Henderson <rth@twiddle.net>, Anthony Perard <anthony.perard@citrix.com>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, "Marc-André Lureau" <marcandre.lureau@redhat.com>, Laurent Vivier <laurent@vivier.eu>, Alistair Francis <Alistair.Francis@wdc.com>, "Michael S. Tsirkin" <mst@redhat.com>, Aurelien Jarno <aurelien@aurel32.net>, Paolo Bonzini <pbonzini@redhat.com>, Thomas Huth <thuth@redhat.com>, Xiao Guangrong <xiaoguangrong.eric@gmail.com>, Paul Durrant <paul@xen.org>, David Gibson <david@gibson.dropbear.id.au>, Stefano Stabellini <sstabellini@kernel.org>

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[PULL 16/31] softfloat: fix floatx80 remainder pseudo-denormal check for zero

Posted by Paolo Bonzini 5 years, 7 months ago

From: Joseph Myers <joseph@codesourcery.com>

The floatx80 remainder implementation ignores the high bit of the
significand when checking whether an operand (numerator) with zero
exponent is zero.  This means it mishandles a pseudo-denormal
representation of 0x1p-16382L by treating it as zero.  Fix this by
checking the whole significand instead.

Signed-off-by: Joseph Myers <joseph@codesourcery.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <alpine.DEB.2.21.2006081655180.23637@digraph.polyomino.org.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 fpu/softfloat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index b7dcf4d6c3..f164b5c0ad 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -5741,7 +5741,7 @@ floatx80 floatx80_modrem(floatx80 a, floatx80 b, bool mod,
         normalizeFloatx80Subnormal( bSig, &bExp, &bSig );
     }
     if ( aExp == 0 ) {
-        if ( (uint64_t) ( aSig0<<1 ) == 0 ) return a;
+        if ( aSig0 == 0 ) return a;
         normalizeFloatx80Subnormal( aSig0, &aExp, &aSig0 );
     }
     bSig |= UINT64_C(0x8000000000000000);
-- 
2.26.2