LibJS: Implement Atomics.load

Author: https://github.com/trflynn89
Commit: https://github.com/SerenityOS/serenity/commit/940875c9fd7
Pull-request: https://github.com/SerenityOS/serenity/pull/8656
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Runtime/AtomicsObject.cpp

@@ -118,6 +118,7 @@ void AtomicsObject::initialize(GlobalObject& global_object)
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.add, add, 3, attr);
+    define_native_function(vm.names.load, load, 2, attr);
 
     // 25.4.15 Atomics [ @@toStringTag ], https://tc39.es/ecma262/#sec-atomics-@@tostringtag
     define_direct_property(*vm.well_known_symbol_to_string_tag(), js_string(global_object.heap(), "Atomics"), Attribute::Configurable);
@@ -141,4 +142,27 @@ JS_DEFINE_NATIVE_FUNCTION(AtomicsObject::add)
     VERIFY_NOT_REACHED();
 }
 
+// 25.4.8 Atomics.load ( typedArray, index ), https://tc39.es/ecma262/#sec-atomics.load
+JS_DEFINE_NATIVE_FUNCTION(AtomicsObject::load)
+{
+    auto* typed_array = typed_array_from(global_object, vm.argument(0));
+    if (!typed_array)
+        return {};
+
+    validate_integer_typed_array(global_object, *typed_array);
+    if (vm.exception())
+        return {};
+
+    auto indexed_position = validate_atomic_access(global_object, *typed_array, vm.argument(1));
+    if (!indexed_position.has_value())
+        return {};
+
+    if (typed_array->viewed_array_buffer()->is_detached()) {
+        vm.throw_exception<TypeError>(global_object, ErrorType::DetachedArrayBuffer);
+        return {};
+    }
+
+    return typed_array->get_value_from_buffer(*indexed_position, ArrayBuffer::Order::SeqCst, true);
+}
+
 }

Userland/Libraries/LibJS/Runtime/AtomicsObject.h

@@ -20,6 +20,7 @@ public:
 
 private:
     JS_DECLARE_NATIVE_FUNCTION(add);
+    JS_DECLARE_NATIVE_FUNCTION(load);
 };
 
 }

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -224,6 +224,7 @@ namespace JS {
     P(lastIndexOf)                           \
     P(length)                                \
     P(link)                                  \
+    P(load)                                  \
     P(log)                                   \
     P(log1p)                                 \
     P(log2)                                  \

Userland/Libraries/LibJS/Tests/builtins/Atomics/Atomics.load.js

@@ -0,0 +1,54 @@
+test("invariants", () => {
+    expect(Atomics.load).toHaveLength(2);
+});
+
+test("error cases", () => {
+    expect(() => {
+        Atomics.load("not an array", 0);
+    }).toThrow(TypeError);
+
+    expect(() => {
+        const bad_array_type = new Float32Array(4);
+        Atomics.load(bad_array_type, 0);
+    }).toThrow(TypeError);
+
+    expect(() => {
+        const bad_array_type = new Uint8ClampedArray(4);
+        Atomics.load(bad_array_type, 0);
+    }).toThrow(TypeError);
+
+    expect(() => {
+        const array = new Int32Array(4);
+        Atomics.load(array, 100);
+    }).toThrow(RangeError);
+});
+
+test("basic functionality (non-BigInt)", () => {
+    [Int8Array, Int16Array, Int32Array, Uint8Array, Uint16Array, Uint32Array].forEach(ArrayType => {
+        const array = new ArrayType(4);
+        array[0] = 1;
+        array[1] = 2;
+        array[2] = 3;
+        array[3] = 4;
+
+        expect(Atomics.load(array, 0)).toBe(1);
+        expect(Atomics.load(array, 1)).toBe(2);
+        expect(Atomics.load(array, 2)).toBe(3);
+        expect(Atomics.load(array, 3)).toBe(4);
+    });
+});
+
+test("basic functionality (BigInt)", () => {
+    [BigInt64Array, BigUint64Array].forEach(ArrayType => {
+        const array = new ArrayType(4);
+        array[0] = 1n;
+        array[1] = 2n;
+        array[2] = 3n;
+        array[3] = 4n;
+
+        expect(Atomics.load(array, 0)).toBe(1n);
+        expect(Atomics.load(array, 1)).toBe(2n);
+        expect(Atomics.load(array, 2)).toBe(3n);
+        expect(Atomics.load(array, 3)).toBe(4n);
+    });
+});