ARROW-13345: [C++] Add basic implementation for log to base b

cpp/src/arrow/compute/api_scalar.cc

@@ -349,6 +349,7 @@ SCALAR_ARITHMETIC_BINARY(Divide, "divide", "divide_checked")
 SCALAR_ARITHMETIC_BINARY(Power, "power", "power_checked")
 SCALAR_ARITHMETIC_BINARY(ShiftLeft, "shift_left", "shift_left_checked")
 SCALAR_ARITHMETIC_BINARY(ShiftRight, "shift_right", "shift_right_checked")
+SCALAR_ARITHMETIC_BINARY(Logb, "logb", "logb_checked")
 SCALAR_EAGER_BINARY(Atan2, "atan2")
 SCALAR_EAGER_UNARY(Floor, "floor")
 SCALAR_EAGER_UNARY(Ceil, "ceil")

cpp/src/arrow/compute/api_scalar.h

@@ -485,6 +485,20 @@ ARROW_EXPORT
 Result<Datum> Log1p(const Datum& arg, ArithmeticOptions options = ArithmeticOptions(),
                     ExecContext* ctx = NULLPTR);
 
+/// \brief Get the log of a value to the given base.
+///
+/// If argument is null the result will be null.
+///
+/// \param[in] arg The values to compute the logarithm for.
+/// \param[in] base The given base.
+/// \param[in] options arithmetic options (overflow handling), optional
+/// \param[in] ctx the function execution context, optional
+/// \return the elementwise log to the given base
+ARROW_EXPORT
+Result<Datum> Logb(const Datum& arg, const Datum& base,
+                   ArithmeticOptions options = ArithmeticOptions(),
+                   ExecContext* ctx = NULLPTR);
+
 /// \brief Round to the nearest integer less than or equal in magnitude to the
 /// argument. Array values can be of arbitrary length. If argument is null the
 /// result will be null.

cpp/src/arrow/compute/kernels/scalar_arithmetic.cc

@@ -817,6 +817,40 @@ struct Log1pChecked {
   }
 };
 
+struct Logb {
+  template <typename T, typename Arg0, typename Arg1>
+  static enable_if_floating_point<T> Call(KernelContext*, Arg0 x, Arg1 base, Status*) {
+    static_assert(std::is_same<T, Arg0>::value, "");
+    static_assert(std::is_same<Arg0, Arg1>::value, "");
+    if (x == 0.0) {
+      if (base == 0.0 || base < 0.0) {
+        return std::numeric_limits<T>::quiet_NaN();
+      } else {
+        return -std::numeric_limits<T>::infinity();
+      }
+    } else if (x < 0.0) {
+      return std::numeric_limits<T>::quiet_NaN();
+    }
+    return std::log(x) / std::log(base);
+  }
+};
+
+struct LogbChecked {
+  template <typename T, typename Arg0, typename Arg1>
+  static enable_if_floating_point<T> Call(KernelContext*, Arg0 x, Arg1 base, Status* st) {
+    static_assert(std::is_same<T, Arg0>::value, "");
+    static_assert(std::is_same<Arg0, Arg1>::value, "");
+    if (x == 0.0 || base == 0.0) {
+      *st = Status::Invalid("logarithm of zero");
+      return x;
+    } else if (x < 0.0 || base < 0.0) {
+      *st = Status::Invalid("logarithm of negative number");
+      return x;
+    }
+    return std::log(x) / std::log(base);
+  }
+};
+
 struct Floor {
   template <typename T, typename Arg>
   static constexpr enable_if_floating_point<T> Call(KernelContext*, Arg arg, Status*) {
@@ -1317,6 +1351,19 @@ std::shared_ptr<ScalarFunction> MakeArithmeticFunctionFloatingPoint(
   return func;
 }
 
+template <typename Op>
+std::shared_ptr<ScalarFunction> MakeArithmeticFunctionFloatingPointNotNull(
+    std::string name, const FunctionDoc* doc) {
+  auto func =
+      std::make_shared<ArithmeticFloatingPointFunction>(name, Arity::Binary(), doc);
+  for (const auto& ty : FloatingPointTypes()) {
+    auto output = is_integer(ty->id()) ? float64() : ty;
+    auto exec = GenerateArithmeticFloatingPoint<ScalarBinaryNotNullEqualTypes, Op>(ty);
+    DCHECK_OK(func->AddKernel({ty, ty}, output, exec));
+  }
+  return func;
+}
+
 const FunctionDoc absolute_value_doc{
     "Calculate the absolute value of the argument element-wise",
     ("Results will wrap around on integer overflow.\n"
@@ -1589,6 +1636,19 @@ const FunctionDoc log1p_checked_doc{
      "-inf or NaN."),
     {"x"}};
 
+const FunctionDoc logb_doc{
+    "Compute log of x to base b of arguments element-wise",
+    ("Values <= -1 return -inf or NaN. Null values return null.\n"
+     "Use function \"logb_checked\" if you want non-positive values to raise an error."),
+    {"x", "b"}};
+
+const FunctionDoc logb_checked_doc{
+    "Compute log of x to base b of arguments element-wise",
+    ("Values <= -1 return -inf or NaN. Null values return null.\n"
+     "Use function \"logb\" if you want non-positive values to return "
+     "-inf or NaN."),
+    {"x", "b"}};
+
 const FunctionDoc floor_doc{
     "Round down to the nearest integer",
     ("Calculate the nearest integer less than or equal in magnitude to the "
@@ -1806,6 +1866,13 @@ void RegisterScalarArithmetic(FunctionRegistry* registry) {
       "log1p_checked", &log1p_checked_doc);
   DCHECK_OK(registry->AddFunction(std::move(log1p_checked)));
 
+  auto logb = MakeArithmeticFunctionFloatingPoint<Logb>("logb", &logb_doc);
+  DCHECK_OK(registry->AddFunction(std::move(logb)));
+
+  auto logb_checked = MakeArithmeticFunctionFloatingPointNotNull<LogbChecked>(
+      "logb_checked", &logb_checked_doc);
+  DCHECK_OK(registry->AddFunction(std::move(logb_checked)));
+
   // ----------------------------------------------------------------------
   // Rounding functions
   auto floor = MakeUnaryArithmeticFunctionFloatingPoint<Floor>("floor", &floor_doc);

cpp/src/arrow/compute/kernels/scalar_arithmetic_test.cc

@@ -229,6 +229,16 @@ class TestBinaryArithmetic : public TestBase {
     AssertBinop(func, lhs, right, expected);
   }
 
+  // (Array, Scalar) => Array
+  void AssertBinop(BinaryFunction func, const std::string& lhs,
+                   const std::shared_ptr<Scalar>& right,
+                   const std::shared_ptr<Array>& expected) {
+    auto left = ArrayFromJSON(type_singleton(), lhs);
+
+    ASSERT_OK_AND_ASSIGN(auto actual, func(left, right, options_, nullptr));
+    ValidateAndAssertApproxEqual(actual.make_array(), expected);
+  }
+
   // (Array, Scalar)
   void AssertBinop(BinaryFunction func, const std::string& lhs,
                    const std::shared_ptr<Scalar>& right, const std::string& expected) {
@@ -248,6 +258,15 @@ class TestBinaryArithmetic : public TestBase {
     AssertBinop(func, left, right, expected);
   }
 
+  // (Array, Array) => Array
+  void AssertBinop(BinaryFunction func, const std::string& lhs, const std::string& rhs,
+                   const std::shared_ptr<Array>& expected) {
+    auto left = ArrayFromJSON(type_singleton(), lhs);
+    auto right = ArrayFromJSON(type_singleton(), rhs);
+
+    AssertBinop(func, left, right, expected);
+  }
+
   // (Array, Array)
   void AssertBinop(BinaryFunction func, const std::shared_ptr<Array>& left,
                    const std::shared_ptr<Array>& right,
@@ -2001,6 +2020,45 @@ TYPED_TEST(TestUnaryArithmeticIntegral, Log) {
   }
 }
 
+TYPED_TEST(TestBinaryArithmeticIntegral, Log) {
+  // Integer arguments promoted to double, sanity check here
+  this->AssertBinop(Logb, "[1, 10, null]", "[10, 10, null]",
+                    ArrayFromJSON(float64(), "[0, 1, null]"));
+  this->AssertBinop(Logb, "[1, 2, null]", "[2, 2, null]",
+                    ArrayFromJSON(float64(), "[0, 1, null]"));
+  this->AssertBinop(Logb, "[10, 100, null]", this->MakeScalar(10),
+                    ArrayFromJSON(float64(), "[1, 2, null]"));
+}
+
+TYPED_TEST(TestBinaryArithmeticFloating, Log) {
+  // Integer arguments promoted to double, sanity check here
+  this->AssertBinop(Logb, "[1.0, 10.0, null]", "[10.0, 10.0, null]", "[0.0, 1.0, null]");
+  this->AssertBinop(Logb, "[1.0, 2.0, null]", "[2.0, 2.0, null]", "[0.0, 1.0, null]");
+  this->AssertBinop(Logb, "[10.0, 100.0, 1000.0, null]", this->MakeScalar(10),
+                    "[1.0, 2.0, 3.0, null]");
+}
+
+TYPED_TEST(TestBinaryArithmeticSigned, Log) {
+  // Integer arguments promoted to double, sanity check here
+  this->SetNansEqual(true);
+  this->SetOverflowCheck(false);
+  this->AssertBinop(Logb, "[-1, 0]", this->MakeScalar(10),
+                    ArrayFromJSON(float64(), "[NaN, -Inf]"));
+  this->AssertBinop(Logb, "[-1, 0]", this->MakeScalar(2),
+                    ArrayFromJSON(float64(), "[NaN, -Inf]"));
+  this->AssertBinop(Logb, "[10, 100]", this->MakeScalar(-1),
+                    ArrayFromJSON(float64(), "[NaN, NaN]"));
+  this->AssertBinop(Logb, "[-1, 0, null]", this->MakeScalar(-1),
+                    ArrayFromJSON(float64(), "[NaN, NaN, null]"));
+  this->AssertBinop(Logb, "[10, 100]", this->MakeScalar(0),
+                    ArrayFromJSON(float64(), "[0, 0]"));
+  this->SetOverflowCheck(true);
+  this->AssertBinopRaises(Logb, "[0]", "[10]", "logarithm of zero");
+  this->AssertBinopRaises(Logb, "[-1]", "[10]", "logarithm of negative number");
+  this->AssertBinopRaises(Logb, "[10]", "[0]", "logarithm of zero");
+  this->AssertBinopRaises(Logb, "[100]", "[-1]", "logarithm of negative number");
+}
+
 TYPED_TEST(TestUnaryArithmeticSigned, Log) {
   // Integer arguments promoted to double, sanity check here
   this->SetNansEqual(true);

docs/source/cpp/compute.rst

@@ -389,6 +389,10 @@ variants that check for domain errors if needed.
 +--------------------------+------------+--------------------+---------------------+
 | log2_checked             | Unary      | Float32/Float64    | Float32/Float64     |
 +--------------------------+------------+--------------------+---------------------+
+| logb                     | Binary     | Float32/Float64    | Float32/Float64     |
++--------------------------+------------+--------------------+---------------------+
+| logb_checked             | Binary     | Float32/Float64    | Float32/Float64     |
++--------------------------+------------+--------------------+---------------------+
 
 Trigonometric functions
 ~~~~~~~~~~~~~~~~~~~~~~~

docs/source/python/api/compute.rst

@@ -104,6 +104,8 @@ variants which detect domain errors.
    log1p_checked
    log2
    log2_checked
+   logb
+   logb_checked
 
 Trigonometric Functions
 -----------------------