https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89459
Bug ID: 89459
Summary: Incorrect rounding for fma in some cases
Product: gcc
Version: 6.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libquadmath
Assignee: unassigned at gcc dot gnu.org
Reporter: andres_takach at mentor dot com
Target Milestone: ---
Created attachment 45802
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45802&action=edit
testcase for issue: c++ fma_rnd_bug.cxx -lquadmath
The function fmaq(x,y,z) should be equivalent to x*y+z if x*y returns a finite
exact value.
Test
x = smallest (subnormal)
hex: 00000000000000000000000000000001
y = 2*(2^112 + 1)
hex: 40700000000000000000000000000001
z = x
fma(x,y,z) returns hex (same as x*y):
00020000000000000000000000000001
x*y+z return hex (it is rounded to nearest even):
00020000000000000000000000000002
GCC version info:
Using built-in specs.
COLLECT_GCC=/wv/hlstools/gcc6.2.0-64/pkgs/dcs_gcc/gcc-6.2.0/lib/gcc/../../bin/c++
COLLECT_LTO_WRAPPER=/wv/hlstools/gcc6.2.0-64/pkgs/dcs_gcc/gcc-6.2.0/lib/gcc/../../libexec/gcc/x86_64-linux-gnu/6.2.0/lto-wrapper
Target: x86_64-linux-gnu
Configured with:
/wv/hls01/dcs_gcc/rls_iwa/2016-09-27_163927/aol/build/src/gcc-6.2.0/configure
--prefix=/wv/hls01/dcs_gcc/rls_iwa/2016-09-27_163927/aol/exports/mgc_home/pkgs/dcs_gcc.aol/gcc-6.2.0
-build=x86_64-linux-gnu --enable-languages=c,c++ --enable-threads --with-dwarf2
--with-pkgversion=Calypto
Thread model: posix
gcc version 6.2.0 (Calypto)
