Fix power function NaN handling so it returns NaN

Summary: The C++ std::pow function returns 1 when 1 is raised to NaN. It returns NaN for every other number except for 1 which is strange. This change makes sure it will return NaN.

Differential Revision: D64145275

velox/functions/prestosql/Arithmetic.h

@@ -229,7 +229,9 @@ struct PowerFunction {
   template <typename TInput>
   FOLLY_ALWAYS_INLINE void
   call(double& result, const TInput& a, const TInput& b) {
-    result = std::pow(a, b);
+    result = std::isnan(a) || std::isnan(b)
+        ? std::numeric_limits<double>::quiet_NaN()
+        : pow(a, b);
   }
 };
 

velox/functions/prestosql/tests/ArithmeticTest.cpp

@@ -279,6 +279,18 @@ TEST_F(ArithmeticTest, power) {
       "pow(c0, c1)", baseDouble, exponentDouble, expectedDouble);
 }
 
+TEST_F(ArithmeticTest, powerNan) {
+  std::vector<double> baseDouble = {1, kNan};
+  std::vector<double> exponentDouble = {kNan, 1};
+  std::vector<double> expectedDouble = {kNan, kNan};
+
+  // Check using function name and alias.
+  assertExpression<double>(
+      "power(c0, c1)", baseDouble, exponentDouble, expectedDouble);
+  assertExpression<double>(
+      "pow(c0, c1)", baseDouble, exponentDouble, expectedDouble);
+}
+
 TEST_F(ArithmeticTest, powerInt) {
   std::vector<int64_t> baseInt = {9, 10, 11, -9, -10, -11, 0};
   std::vector<int64_t> exponentInt = {3, -3, 0, -1, 199999, 77, 0};