Fix rounding in Uint8ClampedArray setter.

src/ia32/macro-assembler-ia32.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 116 matching lines @@
 
 void MacroAssembler::ClampDoubleToUint8(XMMRegister input_reg,
                                         XMMRegister scratch_reg,
                                         Register result_reg) {
   Label done;
   ExternalReference zero_ref = ExternalReference::address_of_zero();
   movdbl(scratch_reg, Operand::StaticVariable(zero_ref));
   Set(result_reg, Immediate(0));
   ucomisd(input_reg, scratch_reg);
   j(below, &done, Label::kNear);
-  ExternalReference half_ref = ExternalReference::address_of_one_half();
-  movdbl(scratch_reg, Operand::StaticVariable(half_ref));
-  addsd(scratch_reg, input_reg);
-  cvttsd2si(result_reg, Operand(scratch_reg));
+  cvtsd2si(result_reg, input_reg);
   test(result_reg, Immediate(0xFFFFFF00));
   j(zero, &done, Label::kNear);
   Set(result_reg, Immediate(255));
   bind(&done);
 }
 
 
 void MacroAssembler::ClampUint8(Register reg) {
   Label done;
   test(reg, Immediate(0xFFFFFF00));
@@ skipping 2773 matching lines @@
   // Load the prototype from the map and loop if non-null.
   bind(&check_prototype);
   mov(ecx, FieldOperand(ebx, Map::kPrototypeOffset));
   cmp(ecx, isolate()->factory()->null_value());
   j(not_equal, &next);
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32