added M records

simulator_SIC_XE/src/loader.cpp

@@ -17,6 +17,7 @@ Loader::~Loader()
 void Loader::load()
 {
     HeaderMetadata header = readHeader();
+    _relocation_address = header.start_address;
       
     while(true) {
         RecordType type = parseRecordType(static_cast<char>(_file_reader->readByte()));
@@ -28,6 +29,11 @@ void Loader::load()
                 }
                 break;
             }
+            case RecordType::MODIFICATION: {
+                ModificationRecord modRecord = readModificationRecord();
+                applyModification(modRecord);
+                break;
+            }
             case RecordType::END: {
                 EndRecord endRecord = readEndRecord();
                 _machine->setPC(endRecord.execution_start_address);
@@ -45,6 +51,7 @@ Loader::RecordType Loader::parseRecordType(char c)
     switch (c) {
         case 'H': return RecordType::HEADER;
         case 'T': return RecordType::TEXT;
+        case 'M': return RecordType::MODIFICATION;
         case 'E': return RecordType::END;
         default: return RecordType::UNKNOWN; // fallback; adjust as needed
     }
@@ -105,6 +112,29 @@ Loader::TextRecord Loader::readTextRecord()
     return record;
 }
 
+Loader::ModificationRecord Loader::readModificationRecord()
+{
+    ModificationRecord record;
+    if(FILE_CONTAINS_WHITE_SPACES) _file_reader->readByte();
+    
+    record.address = std::stoi(_file_reader->readString(6), nullptr, 16);
+    if(FILE_CONTAINS_WHITE_SPACES) _file_reader->readByte();
+    
+    record.length = std::stoi(_file_reader->readString(2), nullptr, 16);
+    
+    record.add = true;
+    std::string rest = _file_reader->readLine();
+    // Remove whitespace
+    rest.erase(std::remove_if(rest.begin(), rest.end(), ::isspace), rest.end());
+    if (!rest.empty()) {
+        if (rest[0] == '-') {
+            record.add = false;
+        }
+    }
+    
+    return record;
+}
+
 Loader::EndRecord Loader::readEndRecord()
 {
     EndRecord record;
@@ -132,3 +162,54 @@ bool Loader::load_into_memory(int start_address, const std::vector<uint8_t> &dat
     }
     return true;
 }
+
+void Loader::applyModification(const ModificationRecord& mod)
+{
+    // M record specifies address and length in half-bytes (nibbles)
+    // We need to modify the value at that address by adding or subtracting
+    // the relocation address
+    
+    int address = mod.address;
+    int halfBytes = mod.length;
+    
+    // Calculate how many full bytes we need to read
+    // halfBytes can be odd or even
+    int numBytes = (halfBytes + 1) / 2;
+    
+    if (address < 0 || address + numBytes > MEMORY_SIZE) {
+        throw std::runtime_error("Modification address out of bounds");
+    }
+    
+    // Read the current value from memory
+    int currentValue = 0;
+    for (int i = 0; i < numBytes; ++i) {
+        currentValue = (currentValue << 8) | _machine->getByte(address + i);
+    }
+    
+    // If odd number of half-bytes, we only modify the relevant nibbles
+    // For simplicity, we'll work with the full bytes and mask appropriately
+    int mask = 0;
+    for (int i = 0; i < halfBytes; ++i) {
+        mask = (mask << 4) | 0xF;
+    }
+    
+    // Extract the value to modify
+    int shift = (numBytes * 2 - halfBytes) * 4;
+    int valueToModify = (currentValue >> shift) & mask;
+    
+    // Apply modification
+    int newValue = mod.add ? (valueToModify + _relocation_address) 
+                           : (valueToModify - _relocation_address);
+    
+    // Mask to keep only the relevant bits
+    newValue &= mask;
+    
+    // Reconstruct the full value
+    int preservedBits = currentValue & ~(mask << shift);
+    int finalValue = preservedBits | (newValue << shift);
+    
+    // Write back to memory (big-endian)
+    for (int i = 0; i < numBytes; ++i) {
+        _machine->setByte(address + i, (finalValue >> ((numBytes - 1 - i) * 8)) & 0xFF);
+    }
+}