MIPS: Fix rounding in Uint8ClampedArray setter.

src/mips/simulator-mips.cc

Index: src/mips/simulator-mips.cc
diff --git a/src/mips/simulator-mips.cc b/src/mips/simulator-mips.cc
index 66d0da71fa4260e086b77b99f8f3773466db5d44..77d64f0782a3c832faa3be86a505b3633d7a1386 100644
--- a/src/mips/simulator-mips.cc
+++ b/src/mips/simulator-mips.cc
@@ -2068,10 +2068,15 @@ void Simulator::DecodeTypeRegister(Instruction* instr) {
               // Rounding modes are not yet supported.
               ASSERT((FCSR_ & 3) == 0);
               // In rounding mode 0 it should behave like ROUND.
-            case ROUND_W_D:  // Round double to word.
+            case ROUND_W_D:  // Round double to word (round half to even).
               {
                 double rounded = fs > 0 ? floor(fs + 0.5) : ceil(fs - 0.5);

[ulan, 2012/08/24 07:21:07]

Why not just do floor(fs + 0.5) for both positive and negative values?

[palfia, 2012/08/24 23:57:29]

Done.

                 int32_t result = static_cast<int32_t>(rounded);
+                if ((result & 1) != 0 && result - fs == 0.5) {

[ulan, 2012/08/24 07:21:07]

This doesn't handle the case when fs is negative, e.g. fs == -4.5, result == -5,
result-fs == -0.5.

[palfia, 2012/08/24 23:57:29]

Using floor(fs + 0.5) above for negative numbers too, this expression becomes
correct:
e.g. fs = -4.5, result = -4 -> result-fs = 0.5
or fs = 4.5, result = 5 -> result-fs = 0.5
It'll be true for all other cases, because we always round half up in the first
step.

[ulan, 2012/08/27 07:23:26]

Yep, thanks for fixing it. :)

+                  // If the number is halfway between two integers,
+                  // round to the even one.
+                  result--;
+                }
                 set_fpu_register(fd_reg, result);
                 if (set_fcsr_round_error(fs, rounded)) {
                   set_fpu_register(fd_reg, kFPUInvalidResult);