s390: improve floating point and integer convertion

src/s390/simulator-s390.cc

Index: src/s390/simulator-s390.cc
diff --git a/src/s390/simulator-s390.cc b/src/s390/simulator-s390.cc
index d387812bd7164097a9a57ad4669171967f60dab2..b669dcb20701c8bebd1fe3e7dfd5cda3574aa094 100644
--- a/src/s390/simulator-s390.cc
+++ b/src/s390/simulator-s390.cc
@@ -6265,10 +6265,21 @@ EVALUATE(CLFEBR) {
 EVALUATE(CLFDBR) {
   DCHECK_OPCODE(CLFDBR);
   DECODE_RRE_INSTRUCTION(r1, r2);
-  double r2_val = get_double_from_d_register(r2);
-  uint32_t r1_val = static_cast<uint32_t>(r2_val);
+  double a = get_double_from_d_register(r2);
+  double n = std::round(a);
+  uint32_t r1_val = static_cast<uint32_t>(n);
   set_low_register(r1, r1_val);
-  SetS390ConvertConditionCode<double>(r2_val, r1_val, UINT32_MAX);
+  if (std::isfinite(a) && a < 0.0) {
+    DCHECK(n <= 0.0 && std::isfinite(n));
+    condition_reg_ = (n < 0.0) ? 0x1 : 0x4;
+  } else if (a == 0.0) {
+    condition_reg_ = 0x8;
+  } else if (std::isfinite(a) && a > 0.0) {
+    DCHECK(n >= 0.0 && std::isfinite(n));
+    condition_reg_ = (n <= static_cast<double>(UINT32_MAX)) ? 0x2 : 0x1;
+  } else {
+    condition_reg_ = 0x1;
+  }
   return length;
 }