LibJS: Add Math.sign()

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/b27834cf164
Pull-request: https://github.com/SerenityOS/serenity/pull/2285

Libraries/LibJS/Runtime/MathObject.cpp

@@ -50,6 +50,7 @@ MathObject::MathObject()
     put_native_function("cos", cos, 1, attr);
     put_native_function("tan", tan, 1, attr);
     put_native_function("pow", pow, 2, attr);
+    put_native_function("sign", sign, 1, attr);
 
     put("E", Value(M_E), 0);
     put("LN2", Value(M_LN2), 0);
@@ -206,4 +207,20 @@ Value MathObject::pow(Interpreter& interpreter)
     return exp(interpreter, interpreter.argument(0), interpreter.argument(1));
 }
 
+Value MathObject::sign(Interpreter& interpreter)
+{
+    auto number = interpreter.argument(0).to_number(interpreter);
+    if (interpreter.exception())
+        return {};
+    if (number.is_positive_zero())
+        return Value(0);
+    if (number.is_negative_zero())
+        return Value(-0.0);
+    if (number.as_double() > 0)
+        return Value(1);
+    if (number.as_double() < 0)
+        return Value(-1);
+    return js_nan();
+}
+
 }

Libraries/LibJS/Runtime/MathObject.h

@@ -51,6 +51,7 @@ private:
     static Value cos(Interpreter&);
     static Value tan(Interpreter&);
     static Value pow(Interpreter&);
+    static Value sign(Interpreter&);
 };
 
 }

Libraries/LibJS/Tests/Math.sign.js

@@ -0,0 +1,42 @@
+load("test-common.js");
+
+function isPositiveZero(value) {
+    return value === 0 && 1 / value === Infinity;
+}
+
+function isNegativeZero(value) {
+    return value === 0 && 1 / value === -Infinity;
+}
+
+try {
+    assert(Math.sign.length === 1);
+
+    assert(Math.sign(0.0001) === 1);
+    assert(Math.sign(1) === 1);
+    assert(Math.sign(42) === 1);
+    assert(Math.sign(Infinity) === 1);
+    assert(isPositiveZero(Math.sign(0)));
+    assert(isPositiveZero(Math.sign(null)));
+    assert(isPositiveZero(Math.sign('')));
+    assert(isPositiveZero(Math.sign([])));
+
+    assert(Math.sign(-0.0001) === -1);
+    assert(Math.sign(-1) === -1);
+    assert(Math.sign(-42) === -1);
+    assert(Math.sign(-Infinity) === -1);
+    assert(isNegativeZero(Math.sign(-0)));
+    assert(isNegativeZero(Math.sign(-null)));
+    assert(isNegativeZero(Math.sign(-'')));
+    assert(isNegativeZero(Math.sign(-[])));
+
+    assert(isNaN(Math.sign()));
+    assert(isNaN(Math.sign(undefined)));
+    assert(isNaN(Math.sign([1, 2, 3])));
+    assert(isNaN(Math.sign({})));
+    assert(isNaN(Math.sign(NaN)));
+    assert(isNaN(Math.sign("foo")));
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}