LibJS: Add spec comments to mul()

1 files changed, 26 insertions, 4 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/Value.cpp b/Userland/Libraries/LibJS/Runtime/Value.cpp
index 93cabf534e..d1dfadd246 100644
--- a/Userland/Libraries/LibJS/Runtime/Value.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Value.cpp
@@ -1764,14 +1764,36 @@ ThrowCompletionOr<Value> sub(VM& vm, Value lhs, Value rhs)
 }
 
 // 13.7 Multiplicative Operators, https://tc39.es/ecma262/#sec-multiplicative-operators
+// MultiplicativeExpression : MultiplicativeExpression MultiplicativeOperator ExponentiationExpression
 ThrowCompletionOr<Value> mul(VM& vm, Value lhs, Value rhs)
 {
+    // 13.15.3 ApplyStringOrNumericBinaryOperator ( lval, opText, rval ), https://tc39.es/ecma262/#sec-applystringornumericbinaryoperator
+    // 1-2, 6. N/A.
+
+    // 3. Let lnum be ? ToNumeric(lval).
     auto lhs_numeric = TRY(lhs.to_numeric(vm));
+
+    // 4. Let rnum be ? ToNumeric(rval).
     auto rhs_numeric = TRY(rhs.to_numeric(vm));
-    if (both_number(lhs_numeric, rhs_numeric))
-        return Value(lhs_numeric.as_double() * rhs_numeric.as_double());
-    if (both_bigint(lhs_numeric, rhs_numeric))
-        return BigInt::create(vm, lhs_numeric.as_bigint().big_integer().multiplied_by(rhs_numeric.as_bigint().big_integer()));
+
+    // 7. Let operation be the abstract operation associated with opText and Type(lnum) in the following table:
+    // [...]
+    // 8. Return operation(lnum, rnum).
+    if (both_number(lhs_numeric, rhs_numeric)) {
+        // 6.1.6.1.4 Number::multiply ( x, y ), https://tc39.es/ecma262/#sec-numeric-types-number-multiply
+        auto x = lhs_numeric.as_double();
+        auto y = rhs_numeric.as_double();
+        return Value(x * y);
+    }
+    if (both_bigint(lhs_numeric, rhs_numeric)) {
+        // 6.1.6.2.4 BigInt::multiply ( x, y ), https://tc39.es/ecma262/#sec-numeric-types-bigint-multiply
+        auto x = lhs_numeric.as_bigint().big_integer();
+        auto y = rhs_numeric.as_bigint().big_integer();
+        // 1. Return the BigInt value that represents the product of x and y.
+        return BigInt::create(vm, x.multiplied_by(y));
+    }
+
+    // 5. If Type(lnum) is different from Type(rnum), throw a TypeError exception.
     return vm.throw_completion<TypeError>(ErrorType::BigIntBadOperatorOtherType, "multiplication");
 }