Inline Doubles truncate and round.

runtime/vm/assembler_ia32.cc

Index: runtime/vm/assembler_ia32.cc
===================================================================
--- runtime/vm/assembler_ia32.cc	(revision 16928)
+++ runtime/vm/assembler_ia32.cc	(working copy)
@@ -809,6 +809,19 @@
 }
 
 
+void Assembler::roundsd(XmmRegister dst, XmmRegister src, RoundingMode mode) {
+  ASSERT(CPUFeatures::sse4_1_supported());
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitUint8(0x66);
+  EmitUint8(0x0F);
+  EmitUint8(0x3A);
+  EmitUint8(0x0B);
+  EmitXmmRegisterOperand(dst, src);
+  // Mask precision exeption.
+  EmitUint8(static_cast<uint8_t>(mode) | 0x8);
+}
+
+
 void Assembler::fldl(const Address& src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0xDD);
@@ -1723,6 +1736,38 @@
 }
 
 
+void Assembler::DoubleRound(XmmRegister dst, XmmRegister src, XmmRegister tmp) {
+  ASSERT(tmp != src);
+  static double kZeroFiveConst = 0.5;
+  static double kNegZeroFiveConst = -0.5;
+  Label is_negative, round;
+  if (src != dst) {
+    movsd(dst, src);
+  }
+  Label below_half, below_equal_neg_half, done;
+  movsd(tmp, Address::Absolute(reinterpret_cast<uword>(&kZeroFiveConst)));
+  comisd(tmp, dst);
+  // 0.5 > dst ?

[Florian Schneider, 2013/01/11 09:49:30]

For consistency with the jump label I'd rewrite the comment to

// dst < 0.5 ?

[srdjan, 2013/01/11 19:41:08]

Done.

+  j(ABOVE, &below_half, Assembler::kNearJump);
+  // floor(val + 0.5).
+  addsd(dst, tmp);
+  roundsd(dst, dst, Assembler::kRoundDown);
+  jmp(&done, Assembler::kNearJump);
+  Bind(&below_half);
+  // Return -0.0 for -0.5.
+  movsd(tmp, Address::Absolute(reinterpret_cast<uword>(&kNegZeroFiveConst)));
+  comisd(tmp, dst);
+  // -0.5 >= dst.

[Florian Schneider, 2013/01/11 09:49:30]

Also here:

dst <= -0.5 ?

[srdjan, 2013/01/11 19:41:08]

Done.

+  j(ABOVE_EQUAL, &below_equal_neg_half, Assembler::kNearJump);
+  roundsd(dst, dst, Assembler::kRoundToZero);
+  jmp(&done, Assembler::kNearJump);
+  Bind(&below_equal_neg_half);
+  addsd(dst, tmp);
+  roundsd(dst, dst, Assembler::kRoundUp);
+  Bind(&done);
+}
+
+
 void Assembler::EnterFrame(intptr_t frame_size) {
   if (prologue_offset_ == -1) {
     prologue_offset_ = CodeSize();