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Fix ldexp implementations.

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The previous implementations produced garbage values if the exponent did
not fit within the exponent bits.  See #2131 for a complete discussion,
and !375 for other possible implementations.

Here we implement the 4-factor version. See `pldexp_impl` in
`GenericPacketMathFunctions.h` for a full description.

The SSE `pcmp*` methods were moved down since `pcmp_le<Packet4i>`
requires `por`.

Left as a "TODO" is to delegate to a faster version if we know the
exponent does fit within the exponent bits.

Fixes #2131.
This commit is contained in:
Antonio Sanchez
2020-10-12 12:24:08 +01:00
committed by Rasmus Munk Larsen
parent 7eb07da538
commit 4cb563a01e
8 changed files with 354 additions and 112 deletions
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35
test/packetmath.cpp
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@@ -573,10 +573,41 @@ void packetmath_real() {
data2[i] = Scalar(internal::random<double>(-1, 1));
}
for (int i = 0; i < PacketSize; ++i) {
data1[i+PacketSize] = Scalar(internal::random<int>(0, 4));
data2[i+PacketSize] = Scalar(internal::random<double>(0, 4));
data1[i+PacketSize] = Scalar(internal::random<int>(-4, 4));
data2[i+PacketSize] = Scalar(internal::random<double>(-4, 4));
}
CHECK_CWISE2_IF(PacketTraits::HasExp, REF_LDEXP, internal::pldexp);
if (PacketTraits::HasExp) {
data1[0] = Scalar(-1);
// underflow to zero
data1[PacketSize] = Scalar(std::numeric_limits<Scalar>::min_exponent-10);
CHECK_CWISE2_IF(PacketTraits::HasExp, REF_LDEXP, internal::pldexp);
// overflow to inf
data1[PacketSize] = Scalar(std::numeric_limits<Scalar>::max_exponent+10);
CHECK_CWISE2_IF(PacketTraits::HasExp, REF_LDEXP, internal::pldexp);
// NaN stays NaN
data1[0] = NumTraits<Scalar>::quiet_NaN();
CHECK_CWISE2_IF(PacketTraits::HasExp, REF_LDEXP, internal::pldexp);
VERIFY((numext::isnan)(data2[0]));
// inf stays inf
data1[0] = NumTraits<Scalar>::infinity();
data1[PacketSize] = Scalar(std::numeric_limits<Scalar>::min_exponent-10);
CHECK_CWISE2_IF(PacketTraits::HasExp, REF_LDEXP, internal::pldexp);
// zero stays zero
data1[0] = Scalar(0);
data1[PacketSize] = Scalar(std::numeric_limits<Scalar>::max_exponent+10);
CHECK_CWISE2_IF(PacketTraits::HasExp, REF_LDEXP, internal::pldexp);
// Small number big exponent.
data1[0] = Scalar(std::ldexp(Scalar(1.0), std::numeric_limits<Scalar>::min_exponent-1));
data1[PacketSize] = Scalar(-std::numeric_limits<Scalar>::min_exponent
+std::numeric_limits<Scalar>::max_exponent);
CHECK_CWISE2_IF(PacketTraits::HasExp, REF_LDEXP, internal::pldexp);
// Big number small exponent.
data1[0] = Scalar(std::ldexp(Scalar(1.0), std::numeric_limits<Scalar>::max_exponent-1));
data1[PacketSize] = Scalar(+std::numeric_limits<Scalar>::min_exponent
-std::numeric_limits<Scalar>::max_exponent);
CHECK_CWISE2_IF(PacketTraits::HasExp, REF_LDEXP, internal::pldexp);
}
for (int i = 0; i < size; ++i) {
data1[i] = Scalar(internal::random<double>(-1, 1) * std::pow(10., internal::random<double>(-6, 6)));