LibJS: Implement exponentiation (** operator)

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/0403845d3ed
Pull-request: https://github.com/SerenityOS/serenity/pull/1627

Libraries/LibJS/AST.cpp

@@ -283,6 +283,8 @@ Value BinaryExpression::execute(Interpreter& interpreter) const
         return div(lhs_result, rhs_result);
     case BinaryOp::Modulo:
         return mod(lhs_result, rhs_result);
+    case BinaryOp::Exponentiation:
+        return exp(lhs_result, rhs_result);
     case BinaryOp::TypedEquals:
         return typed_eq(lhs_result, rhs_result);
     case BinaryOp::TypedInequals:
@@ -421,6 +423,9 @@ void BinaryExpression::dump(int indent) const
     case BinaryOp::Modulo:
         op_string = "%";
         break;
+    case BinaryOp::Exponentiation:
+        op_string = "**";
+        break;
     case BinaryOp::TypedEquals:
         op_string = "===";
         break;

Libraries/LibJS/AST.h

@@ -314,6 +314,7 @@ enum class BinaryOp {
     Multiplication,
     Division,
     Modulo,
+    Exponentiation,
     TypedEquals,
     TypedInequals,
     AbstractEquals,

Libraries/LibJS/Parser.cpp

@@ -470,6 +470,9 @@ NonnullRefPtr<Expression> Parser::parse_secondary_expression(NonnullRefPtr<Expre
     case TokenType::Percent:
         consume();
         return create_ast_node<BinaryExpression>(BinaryOp::Modulo, move(lhs), parse_expression(min_precedence, associativity));
+   case TokenType::DoubleAsterisk:
+        consume();
+        return create_ast_node<BinaryExpression>(BinaryOp::Exponentiation, move(lhs), parse_expression(min_precedence, associativity));
     case TokenType::GreaterThan:
         consume();
         return create_ast_node<BinaryExpression>(BinaryOp::GreaterThan, move(lhs), parse_expression(min_precedence, associativity));
@@ -905,6 +908,7 @@ bool Parser::match_secondary_expression() const
         || type == TokenType::Slash
         || type == TokenType::SlashEquals
         || type == TokenType::Percent
+        || type == TokenType::DoubleAsterisk
         || type == TokenType::Equals
         || type == TokenType::EqualsEqualsEquals
         || type == TokenType::ExclamationMarkEqualsEquals

Libraries/LibJS/Runtime/Value.cpp

@@ -35,6 +35,7 @@
 #include <LibJS/Runtime/PrimitiveString.h>
 #include <LibJS/Runtime/StringObject.h>
 #include <LibJS/Runtime/Value.h>
+#include <math.h>
 
 namespace JS {
 
@@ -268,6 +269,11 @@ Value mod(Value lhs, Value rhs)
     return Value(index - trunc * period);
 }
 
+Value exp(Value lhs, Value rhs)
+{
+    return Value(pow(lhs.to_number().as_double(), rhs.to_number().as_double()));
+}
+
 Value typed_eq(Value lhs, Value rhs)
 {
     if (rhs.type() != lhs.type())

Libraries/LibJS/Runtime/Value.h

@@ -196,6 +196,7 @@ Value sub(Value lhs, Value rhs);
 Value mul(Value lhs, Value rhs);
 Value div(Value lhs, Value rhs);
 Value mod(Value lhs, Value rhs);
+Value exp(Value lhs, Value rhs);
 Value eq(Value lhs, Value rhs);
 Value typed_eq(Value lhs, Value rhs);
 Value instance_of(Value lhs, Value rhs);

Libraries/LibJS/Tests/exponentiation-basic.js

@@ -0,0 +1,30 @@
+function assert(x) { if (!x) throw 1; }
+
+try {
+    assert(2 ** 0 === 1);
+    assert(2 ** 1 === 2);
+    assert(2 ** 2 === 4);
+    assert(2 ** 3 === 8);
+    assert(2 ** -3 === 0.125);
+    assert(3 ** 2 === 9);
+    assert(0 ** 0 === 1);
+    assert(2 ** 3 ** 2 === 512);
+    assert(2 ** (3 ** 2) === 512);
+    assert((2 ** 3) ** 2 === 64);
+    assert("2" ** "3" === 8);
+    assert("" ** [] === 1);
+    assert([] ** null === 1);
+    assert(null ** null === 1);
+    assert(undefined ** null === 1);
+    assert(isNaN(NaN ** 2));
+    assert(isNaN(2 ** NaN));
+    assert(isNaN(undefined ** 2));
+    assert(isNaN(2 ** undefined));
+    assert(isNaN(null ** undefined));
+    assert(isNaN(2 ** "foo"));
+    assert(isNaN("foo" ** 2));
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}

Libraries/LibJS/Tests/modulo-basic.js

@@ -3,7 +3,7 @@ try {
     assert(10.5 % 2.5 === 0.5);
     assert(-0.99 % 0.99 === -0);
 
-    // Examples form MDN:
+    // Examples from MDN:
     // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators
     assert(12 % 5 === 2);
     assert(-1 % 2 === -1);