LibJS: Implement Infinity

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/543c6e00db9
Pull-request: https://github.com/SerenityOS/serenity/pull/1584

Libraries/LibJS/Runtime/GlobalObject.cpp

@@ -18,7 +18,10 @@ GlobalObject::GlobalObject()
     put_native_function("gc", gc);
     put_native_function("isNaN", is_nan);
 
+    // FIXME: These are read-only in ES5
     put("NaN", js_nan());
+    put("Infinity", js_infinity());
+
     put("console", heap().allocate<ConsoleObject>());
     put("Date", heap().allocate<DateConstructor>());
     put("Error", heap().allocate<ErrorConstructor>());

Libraries/LibJS/Runtime/Value.cpp

@@ -57,6 +57,9 @@ String Value::to_string() const
         if (is_nan())
             return "NaN";
 
+        if (is_infinity())
+            return as_double() < 0 ? "-Infinity" : "Infinity";
+
         // FIXME: This needs improvement.
         if ((double)to_i32() == as_double())
             return String::number(to_i32());

Libraries/LibJS/Runtime/Value.h

@@ -54,6 +54,7 @@ public:
     bool is_array() const;
 
     bool is_nan() const { return is_number() && __builtin_isnan(as_double()); }
+    bool is_infinity() const { return is_number() && __builtin_isinf(as_double()); }
 
     Value()
         : m_type(Type::Undefined)
@@ -173,6 +174,11 @@ inline Value js_nan()
     return Value(__builtin_nan(""));
 }
 
+inline Value js_infinity()
+{
+    return Value(__builtin_huge_val());
+}
+
 Value greater_than(Value lhs, Value rhs);
 Value greater_than_equals(Value lhs, Value rhs);
 Value less_than(Value lhs, Value rhs);

Libraries/LibJS/Tests/Infinity-basic.js

@@ -0,0 +1,27 @@
+function assert(x) { if (!x) throw 1; }
+
+try {
+    assert(Infinity + "" === "Infinity");
+    assert(-Infinity + "" === "-Infinity");
+    assert(Infinity === Infinity);
+    assert(Infinity - 1 === Infinity);
+    assert(Infinity + 1 === Infinity);
+    assert(-Infinity === -Infinity);
+    assert(-Infinity - 1 === -Infinity);
+    assert(-Infinity + 1 === -Infinity);
+    assert(1 / Infinity === 0);
+    assert(1 / -Infinity === 0);
+    assert(1 / 0 === Infinity);
+    assert(-1 / 0 === -Infinity);
+    assert(-100 < Infinity);
+    assert(0 < Infinity);
+    assert(100 < Infinity);
+    assert(-Infinity < Infinity);
+    assert(-100 > -Infinity);
+    assert(0 > -Infinity);
+    assert(100 > -Infinity);
+    assert(Infinity > -Infinity);
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}

Libraries/LibJS/Tests/NaN-basic.js

@@ -11,6 +11,7 @@ try {
     assert(isNaN(0) === false);
     assert(isNaN(undefined) === true);
     assert(isNaN(null) === false);
+    assert(isNaN(Infinity) === false);
     console.log("PASS");
 } catch (e) {
     console.log("FAIL: " + e);