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Bug #1777: make the scalar and packet path consistent for the logistic function + respective unit test

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This commit is contained in:
Gael Guennebaud 2020-05-31 00:53:37 +02:00
parent 99b7f7cb9c
commit 029a76e115
2 changed files with 19 additions and 14 deletions
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18
Eigen/src/Core/functors/UnaryFunctors.h
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@ -951,8 +951,7 @@ template <typename T>
struct scalar_logistic_op {
EIGEN_EMPTY_STRUCT_CTOR(scalar_logistic_op)
EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE T operator()(const T& x) const {
const T one = T(1);
return one / (one + numext::exp(-x));
return packetOp(x);
}
template <typename Packet> EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
@ -978,17 +977,7 @@ template <>
struct scalar_logistic_op<float> {
EIGEN_EMPTY_STRUCT_CTOR(scalar_logistic_op)
EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE float operator()(const float& x) const {
// The upper cut-off is the smallest x for which the rational approximation evaluates to 1.
// Choosing this value saves us a few instructions clamping the results at the end.
#ifdef EIGEN_VECTORIZE_FMA
const float cutoff_upper = 15.7243833541870117f;
#else
const float cutoff_upper = 15.6437711715698242f;
#endif
const float cutoff_lower = -9.f;
if (x > cutoff_upper) return 1.0f;
else if (x < cutoff_lower) return numext::exp(x);
else return 1.0f / (1.0f + numext::exp(-x));
return packetOp(x);
}
template <typename Packet> EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
@ -997,7 +986,8 @@ struct scalar_logistic_op<float> {
const Packet lt_mask = pcmp_lt<Packet>(_x, cutoff_lower);
const bool any_small = predux(lt_mask);
// Clamp the input to be at most 'cutoff_upper'.
// The upper cut-off is the smallest x for which the rational approximation evaluates to 1.
// Choosing this value saves us a few instructions clamping the results at the end.
#ifdef EIGEN_VECTORIZE_FMA
const Packet cutoff_upper = pset1<Packet>(15.7243833541870117f);
#else

15
test/packetmath.cpp
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@ -447,6 +447,21 @@ template<typename Scalar,typename Packet> void packetmath_real()
VERIFY((numext::isnan)(data2[0]));
}
{
internal::scalar_logistic_op<Scalar> logistic;
for (int i=0; i<size; ++i)
{
data1[i] = internal::random<Scalar>(-20,20);
}
internal::pstore(data2, logistic.packetOp(internal::pload<Packet>(data1)));
for (int i=0; i<PacketSize; ++i) {
VERIFY_IS_APPROX(data2[i],logistic(data1[i]));
#ifdef EIGEN_VECTORIZE // don't check for exactness when using the i387 FPU
VERIFY_IS_EQUAL(data2[i],logistic(data1[i]));
#endif
}
}
#if EIGEN_HAS_C99_MATH && (__cplusplus > 199711L)
data1[0] = std::numeric_limits<Scalar>::infinity();
data1[1] = Scalar(-1);