Revert of [SAB] Move Atomics builtins to C++

src/builtins/builtins-sharedarraybuffer.cc

Index: src/builtins/builtins-sharedarraybuffer.cc
diff --git a/src/builtins/builtins-sharedarraybuffer.cc b/src/builtins/builtins-sharedarraybuffer.cc
index 85d08bbcee1c4e6be013bcdbaa31abbe964b000c..7ee144901e1a074818704e50886065439ee1234f 100644
--- a/src/builtins/builtins-sharedarraybuffer.cc
+++ b/src/builtins/builtins-sharedarraybuffer.cc
@@ -638,6 +638,61 @@
   return ToObject(isolate, result);
 }
 
+// Uint8Clamped functions
+
+uint8_t ClampToUint8(int32_t value) {
+  if (value < 0) return 0;
+  if (value > 255) return 255;
+  return value;
+}
+
+inline Object* DoCompareExchangeUint8Clamped(Isolate* isolate, void* buffer,
+                                             size_t index,
+                                             Handle<Object> oldobj,
+                                             Handle<Object> newobj) {
+  typedef int32_t convert_type;
+  uint8_t oldval = ClampToUint8(FromObject<convert_type>(oldobj));
+  uint8_t newval = ClampToUint8(FromObject<convert_type>(newobj));
+  uint8_t result = CompareExchangeSeqCst(static_cast<uint8_t*>(buffer) + index,
+                                         oldval, newval);
+  return ToObject(isolate, result);
+}
+
+#define DO_UINT8_CLAMPED_OP(name, op)                                        \
+  inline Object* Do##name##Uint8Clamped(Isolate* isolate, void* buffer,      \
+                                        size_t index, Handle<Object> obj) {  \
+    typedef int32_t convert_type;                                            \
+    uint8_t* p = static_cast<uint8_t*>(buffer) + index;                      \
+    convert_type operand = FromObject<convert_type>(obj);                    \
+    uint8_t expected;                                                        \
+    uint8_t result;                                                          \
+    do {                                                                     \
+      expected = *p;                                                         \
+      result = ClampToUint8(static_cast<convert_type>(expected) op operand); \
+    } while (CompareExchangeSeqCst(p, expected, result) != expected);        \
+    return ToObject(isolate, expected);                                      \
+  }
+
+DO_UINT8_CLAMPED_OP(Add, +)
+DO_UINT8_CLAMPED_OP(Sub, -)
+DO_UINT8_CLAMPED_OP(And, &)
+DO_UINT8_CLAMPED_OP(Or, |)
+DO_UINT8_CLAMPED_OP(Xor, ^)
+
+#undef DO_UINT8_CLAMPED_OP
+
+inline Object* DoExchangeUint8Clamped(Isolate* isolate, void* buffer,
+                                      size_t index, Handle<Object> obj) {
+  typedef int32_t convert_type;
+  uint8_t* p = static_cast<uint8_t*>(buffer) + index;
+  uint8_t result = ClampToUint8(FromObject<convert_type>(obj));
+  uint8_t expected;
+  do {
+    expected = *p;
+  } while (CompareExchangeSeqCst(p, expected, result) != expected);
+  return ToObject(isolate, expected);
+}
+
 }  // anonymous namespace
 
 // Duplicated from objects.h
@@ -686,7 +741,8 @@
 #undef TYPED_ARRAY_CASE
 
     case kExternalUint8ClampedArray:
-      UNREACHABLE();
+      return DoCompareExchangeUint8Clamped(isolate, source, i, expectedValue,
+                                           replacementValue);
 
     default:
       break;
@@ -727,7 +783,7 @@
 #undef TYPED_ARRAY_CASE
 
     case kExternalUint8ClampedArray:
-      UNREACHABLE();
+      return DoAddUint8Clamped(isolate, source, i, value);
 
     default:
       break;
@@ -768,7 +824,7 @@
 #undef TYPED_ARRAY_CASE
 
     case kExternalUint8ClampedArray:
-      UNREACHABLE();
+      return DoSubUint8Clamped(isolate, source, i, value);
 
     default:
       break;
@@ -809,7 +865,7 @@
 #undef TYPED_ARRAY_CASE
 
     case kExternalUint8ClampedArray:
-      UNREACHABLE();
+      return DoAndUint8Clamped(isolate, source, i, value);
 
     default:
       break;
@@ -850,7 +906,7 @@
 #undef TYPED_ARRAY_CASE
 
     case kExternalUint8ClampedArray:
-      UNREACHABLE();
+      return DoOrUint8Clamped(isolate, source, i, value);
 
     default:
       break;
@@ -891,7 +947,7 @@
 #undef TYPED_ARRAY_CASE
 
     case kExternalUint8ClampedArray:
-      UNREACHABLE();
+      return DoXorUint8Clamped(isolate, source, i, value);
 
     default:
       break;
@@ -932,7 +988,7 @@
 #undef TYPED_ARRAY_CASE
 
     case kExternalUint8ClampedArray:
-      UNREACHABLE();
+      return DoExchangeUint8Clamped(isolate, source, i, value);
 
     default:
       break;