Implement byte swapping instructions on MIPS32 and MIPS64.

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>
 
 #if V8_TARGET_ARCH_MIPS
@@ skipping 3815 matching lines @@
                                               0x10101LU >>
                                           16);
 
             output = output | (static_cast<uint32_t>(o_byte << 24));
             input = input >> 8;
           }
 
           alu_out = static_cast<int32_t>(output);
           break;
         }
-        case SEB:
-        case SEH:
-        case WSBH:
-          alu_out = 0x12345678;
-          UNREACHABLE();
+        case SEB: {
+          int8_t input = static_cast<int8_t>(rt());
+          int32_t output = 0x000000FF & input;

[balazs.kilvady, 2016/06/21 10:24:58]

In the above line if input is an int8_t then why do you mask it? Is it needed?
Question for all the similar masks below.

+          int32_t mask = 0x00000080;
+
+          if (mask & input) output += 0xFFFFFF00;
+
+          alu_out = static_cast<int32_t>(output);
           break;
+        }
+        case SEH: {
+          int16_t input = static_cast<int16_t>(rt());
+          int32_t output = 0x0000FFFF & input;
+          int32_t mask = 0x00008000;
+
+          if (mask & input) output += 0xFFFF0000;
+
+          alu_out = static_cast<int32_t>(output);
+          break;
+        }
+        case WSBH: {
+          int32_t input = static_cast<uint32_t>(rt());
+          int32_t output = 0;
+
+          uint32_t mask = 0xFF000000;
+          for (int i = 0; i < 4; i++) {
+            uint32_t tmp = mask & input;
+            if (i % 2 == 0) {
+              tmp = tmp >> 8;
+            } else {
+              tmp = tmp << 8;
+            }
+            output = output | tmp;
+            mask = mask >> 8;
+          }
+
+          alu_out = static_cast<int32_t>(output);
+          break;
+        }
         default: {
           const uint8_t bp = get_instr()->Bp2Value();
           sa >>= kBp2Bits;
           switch (sa) {
             case ALIGN: {
               if (bp == 0) {
                 alu_out = static_cast<int32_t>(rt());
               } else {
                 uint32_t rt_hi = rt() << (8 * bp);
                 uint32_t rs_lo = rs() >> (8 * (4 - bp));
@@ skipping 747 matching lines @@
 
 
 #undef UNSUPPORTED
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // USE_SIMULATOR
 
 #endif  // V8_TARGET_ARCH_MIPS