Fix rounding in Uint8ClampedArray setter.

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
diff --git a/src/arm/macro-assembler-arm.cc b/src/arm/macro-assembler-arm.cc
index 0be9722ca87434174130e45f391ef787c14936f5..4d7198bff68bb108dd9032c44ef8666ebf37dae3 100644
--- a/src/arm/macro-assembler-arm.cc
+++ b/src/arm/macro-assembler-arm.cc
@@ -3684,10 +3684,15 @@ void MacroAssembler::ClampDoubleToUint8(Register result_reg,
 
   // In 0-255 range, round and truncate.
   bind(&in_bounds);
-  Vmov(temp_double_reg, 0.5);
-  vadd(temp_double_reg, input_reg, temp_double_reg);
-  vcvt_u32_f64(temp_double_reg.low(), temp_double_reg);
-  vmov(result_reg, temp_double_reg.low());
+  // Save FPSCR.
+  vmrs(ip);
+  // Set rounding mode to round to the nearest integer by clearing bits[23:22].
+  bic(result_reg, ip, Operand(kVFPRoundingModeMask));
+  vmsr(result_reg);
+  vcvt_s32_f64(input_reg.low(), input_reg, kFPSCRRounding);
+  vmov(result_reg, input_reg.low());
+  // Restore FPSCR.
+  vmsr(ip);

[Yang, 2012/08/22 07:57:07]

Could you use EmitVFPTruncate instead? I'm not entirely sure why it checks for
VFP exceptions. Maybe you should too. Or you could modify EmitVFPTruncate to
make the check optional.

[ulan, 2012/08/22 13:48:17]

The number here is in 0-255 range, so there should be no exceptions.

   bind(&done);
 }