Wipes bytePointer arithmetic off soft VM

Previous implementation of soft VM decoded instructions manually.
Parts of instructions were parsed in the actual code being executed.
This was not clean and error prone.

Current commit removes all pointer arithmetic because all is done
within decoder of TSmalltalkInstruction.

Issue: #32

src/vm.cpp

@@ -253,6 +253,7 @@ SmalltalkVM::TExecuteResult SmalltalkVM::execute(TProcess* p, uint32_t ticks)
         }
 
         // Decoding the instruction
+        const uint16_t lastBytePointer = ec.bytePointer;
         ec.instruction.decodeBytecode(byteCodes, ec.bytePointer);
 
         // And executing it
@@ -295,7 +296,7 @@ SmalltalkVM::TExecuteResult SmalltalkVM::execute(TProcess* p, uint32_t ticks)
             } break;
 
             default:
-                std::fprintf(stderr, "VM: Invalid opcode %d at offset %d in method ", ec.instruction.getOpcode(), ec.bytePointer);
+                std::fprintf(stderr, "VM: Invalid opcode %d at offset %d in method ", ec.instruction.getOpcode(), lastBytePointer);
                 std::fprintf(stderr, "'%s'\n", ec.currentContext->method->name->toString().c_str() );
                 std::exit(1);
         }
@@ -317,11 +318,8 @@ void SmalltalkVM::doPushBlock(TVMExecutionContext& ec)
     // right after the block's body. There we'll probably find the actual invoking code
     // such as sendMessage to a receiver with our block as a parameter or something similar.
 
-    // Reading new byte pointer that points to the code right after the inline block
-    uint16_t newBytePointer = byteCodes[ec.bytePointer] | (byteCodes[ec.bytePointer+1] << 8);
-
-    // Skipping the newBytePointer's data
-    ec.bytePointer += 2;
+    // New byte pointer that points to the code right after the inline block
+    uint16_t newBytePointer = ec.instruction.getExtra();
 
     // Creating block object
     hptr<TBlock> newBlock = newObject<TBlock>();
@@ -333,7 +331,7 @@ void SmalltalkVM::doPushBlock(TVMExecutionContext& ec)
     newBlock->argumentLocation = ec.instruction.getArgument();
     newBlock->blockBytePointer = ec.bytePointer;
 
-    //We set block->bytePointer, stackTop, previousContext when block is invoked
+    // We set block->bytePointer, stackTop, previousContext when block is invoked
 
     // Assigning creatingContext depending on the hierarchy
     // Nested blocks inherit the outer creating context
@@ -598,29 +596,25 @@ SmalltalkVM::TExecuteResult SmalltalkVM::doSpecial(hptr<TProcess>& process, TVME
             break;
 
         case special::branch:
-            ec.bytePointer = byteCodes[ec.bytePointer] | (byteCodes[ec.bytePointer+1] << 8);
+            ec.bytePointer = ec.instruction.getExtra();
             break;
 
         case special::branchIfTrue: {
             ec.returnedValue = ec.stackPop();
 
             if (ec.returnedValue == globals.trueObject)
-                ec.bytePointer = byteCodes[ec.bytePointer] | (byteCodes[ec.bytePointer+1] << 8);
-            else
-                ec.bytePointer += 2;
+                ec.bytePointer = ec.instruction.getExtra();
         } break;
 
         case special::branchIfFalse: {
             ec.returnedValue = ec.stackPop();
 
             if (ec.returnedValue == globals.falseObject)
-                ec.bytePointer = byteCodes[ec.bytePointer] | (byteCodes[ec.bytePointer+1] << 8);
-            else
-                ec.bytePointer += 2;
+                ec.bytePointer = ec.instruction.getExtra();
         } break;
 
         case special::sendToSuper: {
-            uint32_t literalIndex    = byteCodes[ec.bytePointer++];
+            uint32_t literalIndex    = ec.instruction.getExtra();
             TSymbol* messageSelector = literals[literalIndex];
             TClass*  receiverClass   = ec.currentContext->method->klass->parentClass;
             TObjectArray* messageArguments = ec.stackPop<TObjectArray>();
@@ -662,7 +656,7 @@ void SmalltalkVM::doPushConstant(TVMExecutionContext& ec)
 
 SmalltalkVM::TExecuteResult SmalltalkVM::doPrimitive(hptr<TProcess>& process, TVMExecutionContext& ec)
 {
-    uint8_t opcode = (*ec.currentContext->method->byteCodes)[ec.bytePointer++];
+    uint8_t opcode = ec.instruction.getExtra();
 
     // First of all, executing the primitive
     // If primitive succeeds then stop execution of the current method