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Add a note regarding gcc bug #72867

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This commit is contained in:
Gael Guennebaud 2016-09-22 11:18:52 +02:00
parent 4b377715d7
commit 66cbabafed
2 changed files with 7 additions and 2 deletions
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8
Eigen/src/Core/MathFunctionsImpl.h
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@ -29,8 +29,12 @@ T generic_fast_tanh_float(const T& a_x)
// this range is +/-1.0f in single-precision.
const T plus_9 = pset1<T>(9.f);
const T minus_9 = pset1<T>(-9.f);
const T x = pmax(minus_9, pmin(plus_9, a_x));
// NOTE GCC prior to 6.3 might improperly optimize this max/min
// step such that if a_x is nan, x will be either 9 or -9,
// and tanh will return 1 or -1 instead of nan.
// This is supposed to be fixed in gcc6.3,
// see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72867
const T x = pmax(minus_9,pmin(plus_9,a_x));
// The monomial coefficients of the numerator polynomial (odd).
const T alpha_1 = pset1<T>(4.89352455891786e-03f);
const T alpha_3 = pset1<T>(6.37261928875436e-04f);

1
test/packetmath.cpp
View File

@ -365,6 +365,7 @@ template<typename Scalar> void packetmath_real()
}
if (PacketTraits::HasTanh) {
// NOTE this test migh fail with GCC prior to 6.3, see MathFunctionsImpl.h for details.
data1[0] = std::numeric_limits<Scalar>::quiet_NaN();
packet_helper<internal::packet_traits<Scalar>::HasTanh,Packet> h;
h.store(data2, internal::ptanh(h.load(data1)));