Refine a bit ClampXToUint8

src/x64/macro-assembler-x64.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 3121 matching lines @@
 
   CompareMap(obj, map);
   j(not_equal, fail);
 }
 
 
 void MacroAssembler::ClampUint8(Register reg) {
   Label done;
   testl(reg, Immediate(0xFFFFFF00));
   j(zero, &done, Label::kNear);
-  setcc(negative, reg);  // 1 if negative, 0 if positive.
-  decb(reg);  // 0 if negative, 255 if positive.
+  sarl(reg, Immediate(31));
+  notl(reg);  // No zero extension seems to be safe here.
   bind(&done);
 }
 
 
 void MacroAssembler::ClampDoubleToUint8(XMMRegister input_reg,
                                         XMMRegister temp_xmm_reg,
                                         Register result_reg) {
   Label done;
   Label conv_failure;
   xorps(temp_xmm_reg, temp_xmm_reg);
   cvtsd2si(result_reg, input_reg);
   testl(result_reg, Immediate(0xFFFFFF00));
   j(zero, &done, Label::kNear);
   cmpl(result_reg, Immediate(1));
   j(overflow, &conv_failure, Label::kNear);
-  movl(result_reg, Immediate(0));
-  setcc(sign, result_reg);
-  subl(result_reg, Immediate(1));
-  andl(result_reg, Immediate(255));
+  sarl(result_reg, Immediate(31));
+  notl(result_reg);  // No zero extension seems to be safe here.
   jmp(&done, Label::kNear);
   bind(&conv_failure);
+  sarl(result_reg, Immediate(31));
+  ucomisd(input_reg, temp_xmm_reg);
+  j(above_equal, &done, Label::kNear);
   Set(result_reg, 0);
-  ucomisd(input_reg, temp_xmm_reg);
-  j(below, &done, Label::kNear);
-  Set(result_reg, 255);
   bind(&done);
 }
 
 
 void MacroAssembler::LoadUint32(XMMRegister dst,
                                 Register src,
                                 XMMRegister scratch) {
   if (FLAG_debug_code) {
     cmpq(src, Immediate(0xffffffff));
     Assert(below_equal, kInputGPRIsExpectedToHaveUpper32Cleared);
@@ skipping 1902 matching lines @@
   if (ms.shift() > 0) sarl(rdx, Immediate(ms.shift()));
   movl(rax, dividend);
   shrl(rax, Immediate(31));
   addl(rdx, rax);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64