LibJS: Unify exponentiation logic for ** operator and Math.pow

The JS behaviour of exponentiation on two number typed values is
not a simple matter of forwarding to ::pow(double, double). So,
this factors out the Math.pow logic to allow it to be shared with
Value::exp.

Userland/Libraries/LibJS/Runtime/MathObject.cpp

@@ -216,53 +216,7 @@ JS_DEFINE_NATIVE_FUNCTION(MathObject::pow)
 {
     auto base = TRY(vm.argument(0).to_number(global_object));
     auto exponent = TRY(vm.argument(1).to_number(global_object));
-    if (exponent.is_nan())
-        return js_nan();
-    if (exponent.is_positive_zero() || exponent.is_negative_zero())
-        return Value(1);
-    if (base.is_nan())
-        return js_nan();
-    if (base.is_positive_infinity())
-        return exponent.as_double() > 0 ? js_infinity() : Value(0);
-    if (base.is_negative_infinity()) {
-        auto is_odd_integral_number = exponent.is_integral_number() && (exponent.as_i32() % 2 != 0);
-        if (exponent.as_double() > 0)
-            return is_odd_integral_number ? js_negative_infinity() : js_infinity();
-        else
-            return is_odd_integral_number ? Value(-0.0) : Value(0);
-    }
-    if (base.is_positive_zero())
-        return exponent.as_double() > 0 ? Value(0) : js_infinity();
-    if (base.is_negative_zero()) {
-        auto is_odd_integral_number = exponent.is_integral_number() && (exponent.as_i32() % 2 != 0);
-        if (exponent.as_double() > 0)
-            return is_odd_integral_number ? Value(-0.0) : Value(0);
-        else
-            return is_odd_integral_number ? js_negative_infinity() : js_infinity();
-    }
-    VERIFY(base.is_finite_number() && !base.is_positive_zero() && !base.is_negative_zero());
-    if (exponent.is_positive_infinity()) {
-        auto absolute_base = fabs(base.as_double());
-        if (absolute_base > 1)
-            return js_infinity();
-        else if (absolute_base == 1)
-            return js_nan();
-        else if (absolute_base < 1)
-            return Value(0);
-    }
-    if (exponent.is_negative_infinity()) {
-        auto absolute_base = fabs(base.as_double());
-        if (absolute_base > 1)
-            return Value(0);
-        else if (absolute_base == 1)
-            return js_nan();
-        else if (absolute_base < 1)
-            return js_infinity();
-    }
-    VERIFY(exponent.is_finite_number() && !exponent.is_positive_zero() && !exponent.is_negative_zero());
-    if (base.as_double() < 0 && !exponent.is_integral_number())
-        return js_nan();
-    return Value(::pow(base.as_double(), exponent.as_double()));
+    return JS::exp(global_object, base, exponent);
 }
 
 // 21.3.2.14 Math.exp ( x ), https://tc39.es/ecma262/#sec-math.exp

Userland/Libraries/LibJS/Runtime/Value.cpp

@@ -6,6 +6,7 @@
  */
 
 #include <AK/AllOf.h>
+#include <AK/Assertions.h>
 #include <AK/CharacterTypes.h>
 #include <AK/String.h>
 #include <AK/StringBuilder.h>
@@ -1192,6 +1193,58 @@ ThrowCompletionOr<Value> mod(GlobalObject& global_object, Value lhs, Value rhs)
     return vm.throw_completion<TypeError>(global_object, ErrorType::BigIntBadOperatorOtherType, "modulo");
 }
 
+static Value exp_double(Value base, Value exponent)
+{
+    VERIFY(both_number(base, exponent));
+    if (exponent.is_nan())
+        return js_nan();
+    if (exponent.is_positive_zero() || exponent.is_negative_zero())
+        return Value(1);
+    if (base.is_nan())
+        return js_nan();
+    if (base.is_positive_infinity())
+        return exponent.as_double() > 0 ? js_infinity() : Value(0);
+    if (base.is_negative_infinity()) {
+        auto is_odd_integral_number = exponent.is_integral_number() && (exponent.as_i32() % 2 != 0);
+        if (exponent.as_double() > 0)
+            return is_odd_integral_number ? js_negative_infinity() : js_infinity();
+        else
+            return is_odd_integral_number ? Value(-0.0) : Value(0);
+    }
+    if (base.is_positive_zero())
+        return exponent.as_double() > 0 ? Value(0) : js_infinity();
+    if (base.is_negative_zero()) {
+        auto is_odd_integral_number = exponent.is_integral_number() && (exponent.as_i32() % 2 != 0);
+        if (exponent.as_double() > 0)
+            return is_odd_integral_number ? Value(-0.0) : Value(0);
+        else
+            return is_odd_integral_number ? js_negative_infinity() : js_infinity();
+    }
+    VERIFY(base.is_finite_number() && !base.is_positive_zero() && !base.is_negative_zero());
+    if (exponent.is_positive_infinity()) {
+        auto absolute_base = fabs(base.as_double());
+        if (absolute_base > 1)
+            return js_infinity();
+        else if (absolute_base == 1)
+            return js_nan();
+        else if (absolute_base < 1)
+            return Value(0);
+    }
+    if (exponent.is_negative_infinity()) {
+        auto absolute_base = fabs(base.as_double());
+        if (absolute_base > 1)
+            return Value(0);
+        else if (absolute_base == 1)
+            return js_nan();
+        else if (absolute_base < 1)
+            return js_infinity();
+    }
+    VERIFY(exponent.is_finite_number() && !exponent.is_positive_zero() && !exponent.is_negative_zero());
+    if (base.as_double() < 0 && !exponent.is_integral_number())
+        return js_nan();
+    return Value(::pow(base.as_double(), exponent.as_double()));
+}
+
 // 13.6 Exponentiation Operator, https://tc39.es/ecma262/#sec-exp-operator
 ThrowCompletionOr<Value> exp(GlobalObject& global_object, Value lhs, Value rhs)
 {
@@ -1199,7 +1252,7 @@ ThrowCompletionOr<Value> exp(GlobalObject& global_object, Value lhs, Value rhs)
     auto lhs_numeric = TRY(lhs.to_numeric(global_object));
     auto rhs_numeric = TRY(rhs.to_numeric(global_object));
     if (both_number(lhs_numeric, rhs_numeric))
-        return Value(pow(lhs_numeric.as_double(), rhs_numeric.as_double()));
+        return exp_double(lhs_numeric, rhs_numeric);
     if (both_bigint(lhs_numeric, rhs_numeric)) {
         if (rhs_numeric.as_bigint().big_integer().is_negative())
             return vm.throw_completion<RangeError>(global_object, ErrorType::NegativeExponent);

Userland/Libraries/LibJS/Tests/exponentiation-basic.js

@@ -35,3 +35,18 @@ test("exponentiation that produces NaN", () => {
     expect(2 ** "foo").toBeNaN();
     expect("foo" ** 2).toBeNaN();
 });
+
+test("exponentiation with infinities", () => {
+    expect((-1) ** Infinity).toBeNaN();
+    expect(0 ** Infinity).toBe(0);
+    expect(1 ** Infinity).toBeNaN();
+    expect((-1) ** -Infinity).toBeNaN();
+    expect(0 ** -Infinity).toBe(Infinity);
+    expect(1 ** -Infinity).toBeNaN();
+    expect(Infinity ** -1).toBe(0);
+    expect(Infinity ** 0).toBe(1);
+    expect(Infinity ** 1).toBe(Infinity);
+    expect((-Infinity) ** -1).toBe(-0);
+    expect((-Infinity) ** 0).toBe(1);
+    expect((-Infinity) ** 1).toBe(-Infinity);
+});