MIPS: Add rounding support in simulator and RINT instruction.

src/mips/simulator-mips.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <limits.h>
 #include <stdarg.h>
 #include <stdlib.h>
 #include <cmath>
 
 #include "src/v8.h"
@@ skipping 1254 matching lines @@
     FCSR_ &= ~(1 << cc);
   }
 }
 
 
 bool Simulator::test_fcsr_bit(uint32_t cc) {
   return FCSR_ & (1 << cc);
 }
 
 
+void Simulator::set_fcsr_rounding_mode(FPURoundingMode mode) { FCSR_ |= mode; }

[paul.l..., 2015/04/27 05:12:50]

Maybe you should ensure this call does not trash other bits, by doing FCSR_ |=
mode & 3;
In that case, you should probably make a constant kFPURoundingModeMask and use
it here, and just below.

[Djordje.Pesic, 2015/04/27 12:46:58]

Done.

+
+
+unsigned int Simulator::get_fcsr_rounding_mode() { return FCSR_ & 0x3; }
+
+
 // Sets the rounding error codes in FCSR based on the result of the rounding.
 // Returns true if the operation was invalid.
 bool Simulator::set_fcsr_round_error(double original, double rounded) {
   bool ret = false;
   double max_int32 = std::numeric_limits<int32_t>::max();
   double min_int32 = std::numeric_limits<int32_t>::min();
 
   if (!std::isfinite(original) || !std::isfinite(rounded)) {
     set_fcsr_bit(kFCSRInvalidOpFlagBit, true);
     ret = true;
@@ skipping 12 matching lines @@
     set_fcsr_bit(kFCSROverflowFlagBit, true);
     // The reference is not really clear but it seems this is required:
     set_fcsr_bit(kFCSRInvalidOpFlagBit, true);
     ret = true;
   }
 
   return ret;
 }
 
 
+void Simulator::round_according_to_fcsr(double toRound, double& rounded,
+                                        int32_t& rounded_int, double fs) {
+  // 0 RN (round to nearest): Round a result to the nearest
+  // representable value; if the result is exactly halfway between
+  // two representable values, round to zero. Behave like round_w_d

[paul.l..., 2015/04/27 05:12:49]

nit: period at end of this sentence, and 3 more below.

[Djordje.Pesic, 2015/04/27 12:46:58]

Done.

+
+  // 1 RZ (round toward zero): Round a result to the closest
+  // representable value whose absolute value is less than or
+  // equal to the infinitely accurate result. Behave like trunc_w_d
+
+  // 2 RP (round up, or toward  infinity): Round a result to the
+  // next representable value up. Behave like ceil_w_d
+
+  // 3 RD (round down, or toward −infinity): Round a result to
+  // the next representable value down. Behave like floor_w_d
+  switch (get_fcsr_rounding_mode()) {
+    case kRoundToNearest:
+      rounded = std::floor(fs + 0.5);
+      rounded_int = static_cast<int32_t>(rounded);
+      if ((rounded_int & 1) != 0 && rounded_int - fs == 0.5) {
+        // If the number is halfway between two integers,
+        // round to the even one.
+        rounded_int--;
+      }
+      break;
+    case kRoundToZero:
+      rounded = trunc(fs);
+      rounded_int = static_cast<int32_t>(rounded);
+      break;
+    case kRoundToPlusInf:
+      rounded = std::ceil(fs);
+      rounded_int = static_cast<int32_t>(rounded);
+      break;
+    case kRoundToMinusInf:
+      rounded = std::floor(fs);
+      rounded_int = static_cast<int32_t>(rounded);
+      break;
+  }
+}
+
+
 // Raw access to the PC register.
 void Simulator::set_pc(int32_t value) {
   pc_modified_ = true;
   registers_[pc] = value;
 }
 
 
 bool Simulator::has_bad_pc() const {
   return ((registers_[pc] == bad_ra) || (registers_[pc] == end_sim_pc));
 }
@@ skipping 822 matching lines @@
   double ft, fs, fd;
   uint32_t cc, fcsr_cc;
   int64_t i64;
   fs = get_fpu_register_double(fs_reg);
   ft = get_fpu_register_double(ft_reg);
   int64_t ft_int = bit_cast<int64_t>(ft);
   int64_t fd_int = bit_cast<int64_t>(fd);
   cc = instr->FCccValue();
   fcsr_cc = get_fcsr_condition_bit(cc);
   switch (instr->FunctionFieldRaw()) {
+    case RINT: {
+      DCHECK(IsMipsArchVariant(kMips32r6));
+      double result, temp, temp_result;
+      double upper = std::ceil(fs);
+      double lower = std::floor(fs);
+      switch (get_fcsr_rounding_mode()) {
+        case kRoundToNearest:
+          if (upper - fs < fs - lower) {
+            result = upper;
+          } else if (upper - fs > fs - lower) {
+            result = lower;
+          } else {
+            temp_result = upper / 2;
+            double reminder = modf(temp_result, &temp);
+            if (reminder == 0) {
+              result = upper;
+            } else {
+              result = lower;
+            }
+          }
+          break;
+        case kRoundToZero:
+          result = (fs > 0 ? lower : upper);
+          break;
+        case kRoundToPlusInf:
+          result = upper;
+          break;
+        case kRoundToMinusInf:
+          result = lower;
+          break;
+      }
+      set_fpu_register_double(fd_reg, result);
+      if (result != fs) {
+        set_fcsr_bit(kFCSRInexactFlagBit, true);
+      }
+      break;
+    }
     case SEL:
       DCHECK(IsMipsArchVariant(kMips32r6));
       set_fpu_register_double(fd_reg, (fd_int & 0x1) == 0 ? fs : ft);
       break;
     case SELEQZ_C:
       DCHECK(IsMipsArchVariant(kMips32r6));
       set_fpu_register_double(fd_reg, (ft_int & 0x1) == 0 ? fs : 0.0);
       break;
     case SELNEZ_C:
       DCHECK(IsMipsArchVariant(kMips32r6));
@@ skipping 64 matching lines @@
       break;
     case C_ULT_D:
       set_fcsr_bit(fcsr_cc, (fs < ft) || (std::isnan(fs) || std::isnan(ft)));
       break;
     case C_OLE_D:
       set_fcsr_bit(fcsr_cc, (fs <= ft));
       break;
     case C_ULE_D:
       set_fcsr_bit(fcsr_cc, (fs <= ft) || (std::isnan(fs) || std::isnan(ft)));
       break;
-    case CVT_W_D:  // Convert double to word.
-      // Rounding modes are not yet supported.
-      DCHECK((FCSR_ & 3) == 0);
-    // In rounding mode 0 it should behave like ROUND.
+    case CVT_W_D: {  // Convert double to word.
+      double rounded;
+      int32_t result;
+      round_according_to_fcsr(fs, rounded, result, fs);
+      set_fpu_register_word(fd_reg, result);
+      if (set_fcsr_round_error(fs, rounded)) {
+        set_fpu_register_word(fd_reg, kFPUInvalidResult);
+      }
+    } break;
     case ROUND_W_D:  // Round double to word (round half to even).
     {
       double rounded = std::floor(fs + 0.5);
       int32_t result = static_cast<int32_t>(rounded);
       if ((result & 1) != 0 && result - fs == 0.5) {
         // If the number is halfway between two integers,
         // round to the even one.
         result--;
       }
       set_fpu_register_word(fd_reg, result);
@@ skipping 1194 matching lines @@
 }
 
 
 #undef UNSUPPORTED
 
 } }  // namespace v8::internal
 
 #endif  // USE_SIMULATOR
 
 #endif  // V8_TARGET_ARCH_MIPS