x86/x64 port of Math.floor(x/y) to use integer division for specific divisor

src/ia32/disasm-ia32.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 535 matching lines @@
   ASSERT_EQ(0xF7, *data);
   byte modrm = *(data+1);
   int mod, regop, rm;
   get_modrm(modrm, &mod, &regop, &rm);
   if (mod == 3 && regop != 0) {
     const char* mnem = NULL;
     switch (regop) {
       case 2: mnem = "not"; break;
       case 3: mnem = "neg"; break;
       case 4: mnem = "mul"; break;
+      case 5: mnem = "imul"; break;
       case 7: mnem = "idiv"; break;
       default: UnimplementedInstruction();
     }
     AppendToBuffer("%s %s", mnem, NameOfCPURegister(rm));
     return 2;
   } else if (mod == 3 && regop == eax) {
     int32_t imm = *reinterpret_cast<int32_t*>(data+2);
     AppendToBuffer("test %s,0x%x", NameOfCPURegister(rm), imm);
     return 6;
   } else if (regop == eax) {
@@ skipping 1124 matching lines @@
       fprintf(f, "  ");
     }
     fprintf(f, "  %s\n", buffer.start());
   }
 }
 
 
 }  // namespace disasm
 
 #endif  // V8_TARGET_ARCH_IA32