Revert "Add log2() operator to Eigen"

This reverts commit 4d91519a9be061da5d300079fca17dd0b9328050.

13 files changed, 12 insertions, 160 deletions

diff --git a/Eigen/src/Core/GenericPacketMath.h b/Eigen/src/Core/GenericPacketMath.h
index 96c459601..e2fc7002b 100644
--- a/Eigen/src/Core/GenericPacketMath.h
+++ b/Eigen/src/Core/GenericPacketMath.h
@@ -650,13 +650,6 @@ Packet plog1p(const Packet& a) { return numext::log1p(a); }
 template<typename Packet> EIGEN_DECLARE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
 Packet plog10(const Packet& a) { EIGEN_USING_STD(log10); return log10(a); }
 
-/** \internal \returns the log10 of \a a (coeff-wise) */
-template<typename Packet> EIGEN_DECLARE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
-Packet plog2(const Packet& a) {
-  typedef typename internal::unpacket_traits<Packet>::type Scalar;
-  return pmul(pset1<Packet>(Scalar(M_LOG2E)), plog(a)); 
-}
-
 /** \internal \returns the square-root of \a a (coeff-wise) */
 template<typename Packet> EIGEN_DECLARE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
 Packet psqrt(const Packet& a) { EIGEN_USING_STD(sqrt); return sqrt(a); }
diff --git a/Eigen/src/Core/GlobalFunctions.h b/Eigen/src/Core/GlobalFunctions.h
index 629af94b9..0a539ed8e 100644
--- a/Eigen/src/Core/GlobalFunctions.h
+++ b/Eigen/src/Core/GlobalFunctions.h
@@ -81,8 +81,7 @@ namespace Eigen
   EIGEN_ARRAY_DECLARE_GLOBAL_UNARY(expm1,scalar_expm1_op,exponential of a value minus 1,\sa ArrayBase::expm1)
   EIGEN_ARRAY_DECLARE_GLOBAL_UNARY(log,scalar_log_op,natural logarithm,\sa Eigen::log10 DOXCOMMA ArrayBase::log)
   EIGEN_ARRAY_DECLARE_GLOBAL_UNARY(log1p,scalar_log1p_op,natural logarithm of 1 plus the value,\sa ArrayBase::log1p)
-  EIGEN_ARRAY_DECLARE_GLOBAL_UNARY(log10,scalar_log10_op,base 10 logarithm,\sa Eigen::log DOXCOMMA ArrayBase::log10)
-  EIGEN_ARRAY_DECLARE_GLOBAL_UNARY(log2,scalar_log2_op,base 2 logarithm,\sa Eigen::log DOXCOMMA ArrayBase::log2)
+  EIGEN_ARRAY_DECLARE_GLOBAL_UNARY(log10,scalar_log10_op,base 10 logarithm,\sa Eigen::log DOXCOMMA ArrayBase::log)
   EIGEN_ARRAY_DECLARE_GLOBAL_UNARY(abs,scalar_abs_op,absolute value,\sa ArrayBase::abs DOXCOMMA MatrixBase::cwiseAbs)
   EIGEN_ARRAY_DECLARE_GLOBAL_UNARY(abs2,scalar_abs2_op,squared absolute value,\sa ArrayBase::abs2 DOXCOMMA MatrixBase::cwiseAbs2)
   EIGEN_ARRAY_DECLARE_GLOBAL_UNARY(arg,scalar_arg_op,complex argument,\sa ArrayBase::arg DOXCOMMA MatrixBase::cwiseArg)
diff --git a/Eigen/src/Core/arch/AVX/MathFunctions.h b/Eigen/src/Core/arch/AVX/MathFunctions.h
index 5fe2cff32..e2e704d82 100644
--- a/Eigen/src/Core/arch/AVX/MathFunctions.h
+++ b/Eigen/src/Core/arch/AVX/MathFunctions.h
@@ -42,18 +42,6 @@ plog<Packet4d>(const Packet4d& _x) {
   return plog_double(_x);
 }
 
-template <>
-EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED Packet8f
-plog2<Packet8f>(const Packet8f& _x) {
-  return plog2_float(_x);
-}
-
-template <>
-EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED Packet4d
-plog2<Packet4d>(const Packet4d& _x) {
-  return plog2_double(_x);
-}
-
 template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
 Packet8f plog1p<Packet8f>(const Packet8f& _x) {
   return generic_plog1p(_x);
@@ -173,7 +161,6 @@ Packet4d prsqrt<Packet4d>(const Packet4d& _x) {
 F16_PACKET_FUNCTION(Packet8f, Packet8h, psin)
 F16_PACKET_FUNCTION(Packet8f, Packet8h, pcos)
 F16_PACKET_FUNCTION(Packet8f, Packet8h, plog)
-F16_PACKET_FUNCTION(Packet8f, Packet8h, plog2)
 F16_PACKET_FUNCTION(Packet8f, Packet8h, plog1p)
 F16_PACKET_FUNCTION(Packet8f, Packet8h, pexpm1)
 F16_PACKET_FUNCTION(Packet8f, Packet8h, pexp)
@@ -184,7 +171,6 @@ F16_PACKET_FUNCTION(Packet8f, Packet8h, prsqrt)
 BF16_PACKET_FUNCTION(Packet8f, Packet8bf, psin)
 BF16_PACKET_FUNCTION(Packet8f, Packet8bf, pcos)
 BF16_PACKET_FUNCTION(Packet8f, Packet8bf, plog)
-BF16_PACKET_FUNCTION(Packet8f, Packet8bf, plog2)
 BF16_PACKET_FUNCTION(Packet8f, Packet8bf, plog1p)
 BF16_PACKET_FUNCTION(Packet8f, Packet8bf, pexpm1)
 BF16_PACKET_FUNCTION(Packet8f, Packet8bf, pexp)
diff --git a/Eigen/src/Core/arch/AVX512/MathFunctions.h b/Eigen/src/Core/arch/AVX512/MathFunctions.h
index 66f3252cd..c04da6795 100644
--- a/Eigen/src/Core/arch/AVX512/MathFunctions.h
+++ b/Eigen/src/Core/arch/AVX512/MathFunctions.h
@@ -50,21 +50,6 @@ plog<Packet8d>(const Packet8d& _x) {
 F16_PACKET_FUNCTION(Packet16f, Packet16h, plog)
 BF16_PACKET_FUNCTION(Packet16f, Packet16bf, plog)
 
-template <>
-EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED Packet16f
-plog2<Packet16f>(const Packet16f& _x) {
-  return plog2_float(_x);
-}
-
-template <>
-EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED Packet8d
-plog2<Packet8d>(const Packet8d& _x) {
-  return plog2_double(_x);
-}
-
-F16_PACKET_FUNCTION(Packet16f, Packet16h, plog2)
-BF16_PACKET_FUNCTION(Packet16f, Packet16bf, plog2)
-
 // Exponential function. Works by writing "x = m*log(2) + r" where
 // "m = floor(x/log(2)+1/2)" and "r" is the remainder. The result is then
 // "exp(x) = 2^m*exp(r)" where exp(r) is in the range [-1,1).
diff --git a/Eigen/src/Core/arch/Default/BFloat16.h b/Eigen/src/Core/arch/Default/BFloat16.h
index 616dcf667..351f451a3 100644
--- a/Eigen/src/Core/arch/Default/BFloat16.h
+++ b/Eigen/src/Core/arch/Default/BFloat16.h
@@ -512,9 +512,6 @@ EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC bfloat16 log1p(const bfloat16& a) {
 EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC bfloat16 log10(const bfloat16& a) {
   return bfloat16(::log10f(float(a)));
 }
-EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC bfloat16 log2(const bfloat16& a) {
-  return bfloat16(static_cast<float>(M_LOG2E) * ::logf(float(a)));
-}
 EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC bfloat16 sqrt(const bfloat16& a) {
     return bfloat16(::sqrtf(float(a)));
 }
diff --git a/Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h b/Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h
index c6bb89b05..60db2e12f 100644
--- a/Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h
+++ b/Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h
@@ -59,16 +59,16 @@ pldexp_double(Packet a, Packet exponent)
   return pmul(a, preinterpret<Packet>(plogical_shift_left<52>(ei)));
 }
 
-// Natural or base 2 logarithm.
+// Natural logarithm
 // Computes log(x) as log(2^e * m) = C*e + log(m), where the constant C =log(2)
 // and m is in the range [sqrt(1/2),sqrt(2)). In this range, the logarithm can
 // be easily approximated by a polynomial centered on m=1 for stability.
 // TODO(gonnet): Further reduce the interval allowing for lower-degree
 //               polynomial interpolants -> ... -> profit!
-template <typename Packet, bool base2>
+template <typename Packet>
 EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
 EIGEN_UNUSED
-Packet plog_impl_float(const Packet _x)
+Packet plog_float(const Packet _x)
 {
   Packet x = _x;
 
@@ -131,13 +131,8 @@ Packet plog_impl_float(const Packet _x)
   x = padd(x, y);
 
   // Add the logarithm of the exponent back to the result of the interpolation.
-  if (base2) {
-    const Packet cst_log2e = pset1<Packet>(static_cast<float>(M_LOG2E));
-    x = pmadd(x, cst_log2e, e);
-  } else {
-    const Packet cst_ln2 = pset1<Packet>(static_cast<float>(M_LN2));
-    x = pmadd(e, cst_ln2, x);
-  }
+  const Packet cst_ln2 = pset1<Packet>(M_LN2);
+  x = pmadd(e, cst_ln2, x);
 
   Packet invalid_mask = pcmp_lt_or_nan(_x, pzero(_x));
   Packet iszero_mask  = pcmp_eq(_x,pzero(_x));
@@ -150,23 +145,8 @@ Packet plog_impl_float(const Packet _x)
                               por(pselect(pos_inf_mask,cst_pos_inf,x), invalid_mask));
 }
 
-template <typename Packet>
-EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
-EIGEN_UNUSED
-Packet plog_float(const Packet _x)
-{
-  return plog_impl_float<Packet, /* base2 */ false>(_x);
-}
-
-template <typename Packet>
-EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
-EIGEN_UNUSED
-Packet plog2_float(const Packet _x)
-{
-  return plog_impl_float<Packet, /* base2 */ true>(_x);
-}
 
-/* Returns the base e (2.718...) or base 2 logarithm of x.
+/* Returns the base e (2.718...) logarithm of x.
  * The argument is separated into its exponent and fractional parts.
  * The logarithm of the fraction in the interval [sqrt(1/2), sqrt(2)],
  * is approximated by
@@ -175,16 +155,16 @@ Packet plog2_float(const Packet _x)
  *
  * for more detail see: http://www.netlib.org/cephes/
  */
-template <typename Packet, bool base2>
+template <typename Packet>
 EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
 EIGEN_UNUSED
-Packet plog_impl_double(const Packet _x)
+Packet plog_double(const Packet _x)
 {
   Packet x = _x;
 
   const Packet cst_1              = pset1<Packet>(1.0);
   const Packet cst_neg_half       = pset1<Packet>(-0.5);
-  // The smallest non denormalized double.
+  // The smallest non denormalized float number.
   const Packet cst_min_norm_pos   = pset1frombits<Packet>( static_cast<uint64_t>(0x0010000000000000ull));
   const Packet cst_minus_inf      = pset1frombits<Packet>( static_cast<uint64_t>(0xfff0000000000000ull));
   const Packet cst_pos_inf        = pset1frombits<Packet>( static_cast<uint64_t>(0x7ff0000000000000ull));
@@ -252,13 +232,8 @@ Packet plog_impl_double(const Packet _x)
   x = padd(x, y);
 
   // Add the logarithm of the exponent back to the result of the interpolation.
-  if (base2) {
-    const Packet cst_log2e = pset1<Packet>(M_LOG2E);
-    x = pmadd(x, cst_log2e, e);
-  } else {
-    const Packet cst_ln2 = pset1<Packet>(M_LN2);
-    x = pmadd(e, cst_ln2, x);
-  }
+  const Packet cst_ln2 = pset1<Packet>(M_LN2);
+  x = pmadd(e, cst_ln2, x);
 
   Packet invalid_mask = pcmp_lt_or_nan(_x, pzero(_x));
   Packet iszero_mask  = pcmp_eq(_x,pzero(_x));
@@ -271,22 +246,6 @@ Packet plog_impl_double(const Packet _x)
                               por(pselect(pos_inf_mask,cst_pos_inf,x), invalid_mask));
 }
 
-template <typename Packet>
-EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
-EIGEN_UNUSED
-Packet plog_double(const Packet _x)
-{
-  return plog_impl_double<Packet, /* base2 */ false>(_x);
-}
-
-template <typename Packet>
-EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
-EIGEN_UNUSED
-Packet plog2_double(const Packet _x)
-{
-  return plog_impl_double<Packet, /* base2 */ true>(_x);
-}
-
 /** \internal \returns log(1 + x) computed using W. Kahan's formula.
     See: http://www.plunk.org/~hatch/rightway.php
  */
diff --git a/Eigen/src/Core/arch/Default/GenericPacketMathFunctionsFwd.h b/Eigen/src/Core/arch/Default/GenericPacketMathFunctionsFwd.h
index b0f0b78fc..0e02a1b20 100644
--- a/Eigen/src/Core/arch/Default/GenericPacketMathFunctionsFwd.h
+++ b/Eigen/src/Core/arch/Default/GenericPacketMathFunctionsFwd.h
@@ -32,24 +32,12 @@ EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
 EIGEN_UNUSED
 Packet plog_float(const Packet _x);
 
-/** \internal \returns log2(x) for single precision float */
-template <typename Packet>
-EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
-EIGEN_UNUSED
-Packet plog2_float(const Packet _x);
-
 /** \internal \returns log(x) for single precision float */
 template <typename Packet>
 EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
 EIGEN_UNUSED
 Packet plog_double(const Packet _x);
 
-/** \internal \returns log2(x) for single precision float */
-template <typename Packet>
-EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
-EIGEN_UNUSED
-Packet plog2_double(const Packet _x);
-
 /** \internal \returns log(1 + x) */
 template<typename Packet>
 Packet generic_plog1p(const Packet& x);
diff --git a/Eigen/src/Core/arch/Default/Half.h b/Eigen/src/Core/arch/Default/Half.h
index db85f4edf..7029c500d 100644
--- a/Eigen/src/Core/arch/Default/Half.h
+++ b/Eigen/src/Core/arch/Default/Half.h
@@ -622,10 +622,6 @@ EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC half log1p(const half& a) {
 EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC half log10(const half& a) {
   return half(::log10f(float(a)));
 }
-EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC half log2(const half& a) {
-  return half(static_cast<float>(M_LOG2E) * ::logf(float(a)));
-}
-
 EIGEN_STRONG_INLINE EIGEN_DEVICE_FUNC half sqrt(const half& a) {
 #if (EIGEN_CUDA_SDK_VER >= 80000 && defined EIGEN_CUDA_ARCH && EIGEN_CUDA_ARCH >= 530) || \
   defined(EIGEN_HIP_DEVICE_COMPILE)
diff --git a/Eigen/src/Core/arch/SSE/MathFunctions.h b/Eigen/src/Core/arch/SSE/MathFunctions.h
index 2d7df2f7b..d5b62e86a 100644
--- a/Eigen/src/Core/arch/SSE/MathFunctions.h
+++ b/Eigen/src/Core/arch/SSE/MathFunctions.h
@@ -30,16 +30,6 @@ Packet2d plog<Packet2d>(const Packet2d& _x) {
 }
 
 template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
-Packet4f plog2<Packet4f>(const Packet4f& _x) {
-  return plog2_float(_x);
-}
-
-template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
-Packet2d plog2<Packet2d>(const Packet2d& _x) {
-  return plog2_double(_x);
-}
-
-template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
 Packet4f plog1p<Packet4f>(const Packet4f& _x) {
   return generic_plog1p(_x);
 }
diff --git a/Eigen/src/Core/functors/UnaryFunctors.h b/Eigen/src/Core/functors/UnaryFunctors.h
index c037576dc..8c0ed8481 100644
--- a/Eigen/src/Core/functors/UnaryFunctors.h
+++ b/Eigen/src/Core/functors/UnaryFunctors.h
@@ -396,22 +396,6 @@ struct functor_traits<scalar_log10_op<Scalar> >
 { enum { Cost = 5 * NumTraits<Scalar>::MulCost, PacketAccess = packet_traits<Scalar>::HasLog10 }; };
 
 /** \internal
-  *
-  * \brief Template functor to compute the base-2 logarithm of a scalar
-  *
-  * \sa class CwiseUnaryOp, Cwise::log2()
-  */
-template<typename Scalar> struct scalar_log2_op {
-  EIGEN_EMPTY_STRUCT_CTOR(scalar_log2_op)
-  EIGEN_DEVICE_FUNC inline const Scalar operator() (const Scalar& a) const { return Scalar(M_LOG2E) * std::log(a); }
-  template <typename Packet>
-  EIGEN_DEVICE_FUNC inline Packet packetOp(const Packet& a) const { return internal::plog2(a); }
-};
-template<typename Scalar>
-struct functor_traits<scalar_log2_op<Scalar> >
-{ enum { Cost = 5 * NumTraits<Scalar>::MulCost, PacketAccess = packet_traits<Scalar>::HasLog }; };
-
-/** \internal
   * \brief Template functor to compute the square root of a scalar
   * \sa class CwiseUnaryOp, Cwise::sqrt()
   */
diff --git a/Eigen/src/plugins/ArrayCwiseUnaryOps.h b/Eigen/src/plugins/ArrayCwiseUnaryOps.h
index b7ea22a9d..59a4ee6a0 100644
--- a/Eigen/src/plugins/ArrayCwiseUnaryOps.h
+++ b/Eigen/src/plugins/ArrayCwiseUnaryOps.h
@@ -14,7 +14,6 @@ typedef CwiseUnaryOp<internal::scalar_expm1_op<Scalar>, const Derived> Expm1Retu
 typedef CwiseUnaryOp<internal::scalar_log_op<Scalar>, const Derived> LogReturnType;
 typedef CwiseUnaryOp<internal::scalar_log1p_op<Scalar>, const Derived> Log1pReturnType;
 typedef CwiseUnaryOp<internal::scalar_log10_op<Scalar>, const Derived> Log10ReturnType;
-typedef CwiseUnaryOp<internal::scalar_log2_op<Scalar>, const Derived> Log2ReturnType;
 typedef CwiseUnaryOp<internal::scalar_cos_op<Scalar>, const Derived> CosReturnType;
 typedef CwiseUnaryOp<internal::scalar_sin_op<Scalar>, const Derived> SinReturnType;
 typedef CwiseUnaryOp<internal::scalar_tan_op<Scalar>, const Derived> TanReturnType;
@@ -160,18 +159,6 @@ log10() const
   return Log10ReturnType(derived());
 }
 
-/** \returns an expression of the coefficient-wise base-2 logarithm of *this.
-  *
-  * This function computes the coefficient-wise base-2 logarithm.
-  *
-  */
-EIGEN_DEVICE_FUNC
-inline const Log2ReturnType
-log2() const
-{
-  return Log2ReturnType(derived());
-}
-
 /** \returns an expression of the coefficient-wise square root of *this.
   *
   * This function computes the coefficient-wise square root. The function MatrixBase::sqrt() in the
diff --git a/test/array_cwise.cpp b/test/array_cwise.cpp
index 6910f0e1f..48c0935a4 100644
--- a/test/array_cwise.cpp
+++ b/test/array_cwise.cpp
@@ -319,7 +319,6 @@ template<typename ArrayType> void array_real(const ArrayType& m)
   VERIFY_IS_APPROX(m3.log(), log(m3));
   VERIFY_IS_APPROX(m3.log1p(), log1p(m3));
   VERIFY_IS_APPROX(m3.log10(), log10(m3));
-  VERIFY_IS_APPROX(m3.log2(), log2(m3));
 
 
   VERIFY((!(m1>m2) == (m1<=m2)).all());
@@ -373,7 +372,6 @@ template<typename ArrayType> void array_real(const ArrayType& m)
   VERIFY_IS_APPROX(pow(m3,RealScalar(-0.5)), m3.rsqrt());
 
   VERIFY_IS_APPROX(log10(m3), log(m3)/log(10));
-  VERIFY_IS_APPROX(log2(m3), log(m3)/log(2));
 
   // scalar by array division
   const RealScalar tiny = sqrt(std::numeric_limits<RealScalar>::epsilon());
@@ -425,7 +423,6 @@ template<typename ArrayType> void array_complex(const ArrayType& m)
   VERIFY_IS_APPROX(m1.inverse(), inverse(m1));
   VERIFY_IS_APPROX(m1.log(), log(m1));
   VERIFY_IS_APPROX(m1.log10(), log10(m1));
-  VERIFY_IS_APPROX(m1.log2(), log2(m1));
   VERIFY_IS_APPROX(m1.abs(), abs(m1));
   VERIFY_IS_APPROX(m1.abs2(), abs2(m1));
   VERIFY_IS_APPROX(m1.sqrt(), sqrt(m1));
@@ -481,7 +478,6 @@ template<typename ArrayType> void array_complex(const ArrayType& m)
   VERIFY_IS_APPROX(abs(m1), sqrt(square(m1.real())+square(m1.imag())));
   VERIFY_IS_APPROX(abs(m1), sqrt(abs2(m1)));
   VERIFY_IS_APPROX(log10(m1), log(m1)/log(10));
-  VERIFY_IS_APPROX(log2(m1), log(m1)/log(2));
 
   VERIFY_IS_APPROX( m1.sign(), -(-m1).sign() );
   VERIFY_IS_APPROX( m1.sign() * m1.abs(), m1);
diff --git a/test/packetmath.cpp b/test/packetmath.cpp
index d995e8b71..ae0ead820 100644
--- a/test/packetmath.cpp
+++ b/test/packetmath.cpp
@@ -488,13 +488,6 @@ void packetmath() {
   packetmath_minus_zero_add<Scalar, Packet>();
 }
 
-// Notice that this definition works for complex types as well.
-// c++11 has std::log2 for real, but not for complex types.
-template <typename Scalar>
-Scalar log2(Scalar x) {
-  return Scalar(M_LOG2E) * std::log(x);
-}
-
 template <typename Scalar, typename Packet>
 void packetmath_real() {
   typedef internal::packet_traits<Scalar> PacketTraits;
@@ -513,7 +506,6 @@ void packetmath_real() {
   if (internal::random<float>(0, 1) < 0.1f) data1[internal::random<int>(0, PacketSize)] = Scalar(0);
 
   CHECK_CWISE1_IF(PacketTraits::HasLog, std::log, internal::plog);
-  CHECK_CWISE1_IF(PacketTraits::HasLog, log2, internal::plog2);
   CHECK_CWISE1_IF(PacketTraits::HasRsqrt, 1 / std::sqrt, internal::prsqrt);
 
   for (int i = 0; i < size; ++i) {