//------------------------------------------------------------------------------------------------------------
private void ifStatement(string[] tokens, int lineNumber)
{
// Assume only one token to the left of the comparator eg. 20 if x == y goto 50
// [2] = Left, [3] = Comparator, [4] = Right, [5] = 'goto', [6] = LineNumber
if (!tokens.Contains("goto"))
{
throw new SystemException($"'if' statement missing corresponding 'goto' -on code line {lineNumber}");
}
string left = tokens[2];
string comparator = tokens[3];
string right = tokens[4];
string goTo = tokens[5];
string gotoLine = tokens[6];
TableEntry leftEntry, rightEntry;
//------------------Begin Validations--------Symbol table update------------
// Validate left of comparator
if (Int32.TryParse(left, out int intLeft)) // Third token is a number (constant)
{
leftEntry = _symbolTable.FindOrAddConst(intLeft);
_compiledCode.Add(leftEntry.Symbol(), leftEntry.Location());
}
else if (Toolbelt.IsValidVariable(left)) // Third token is a valid variable
{
char leftVar = Convert.ToChar(left);
leftEntry = _symbolTable.FindOrAddVar((int)leftVar);
}
else
{
throw new SystemException($"{left} not valid following 'if' keyword -on code line {lineNumber}");
}
// Validate comparator
if (!Toolbelt.IsComparator(comparator)) // Fourth token is a valid comparator
{
throw new SystemException($"{comparator} is is not a valid comparator in 'if' statement -on code line {lineNumber}");
}
// Validate left of comparator
if (Int32.TryParse(right, out int intRight)) // Third token is a number (constant)
{
rightEntry = _symbolTable.FindOrAddConst(intRight);
_compiledCode.Add(rightEntry.Symbol(), rightEntry.Location());
}
else if (Toolbelt.IsValidVariable(right)) // Third token is a valid variable
{
char rightVar = Convert.ToChar(right);
rightEntry = _symbolTable.FindOrAddVar((int)rightVar);
}
else
{
throw new SystemException($"{right} not valid following comparator in 'if' statement -on code line {lineNumber}");
}
// validate that 'goto' is in position 5
if (goTo != "goto")
{
throw new SystemException($"Expected 'goto' after comparison in 'if' statement. ({goTo}) -on code line {lineNumber}");
}
// validate that following the 'goto' is a numeric value
if (!Int32.TryParse(gotoLine, out int intGotoLine))
{
throw new SystemException($"'{gotoLine}' invalid token following 'goto' in 'if' statement. Integer value expected. -on code line {lineNumber}");
}
//-------------End Validations--------------------
if (leftEntry == null || rightEntry == null)
{
throw new SystemException($"Unknown error occurred in 'if/goto' statement -on code line {lineNumber}");
}
// lookup goto line number in symbol table
var gotoLineEntry = _symbolTable.FindLineNumber(intGotoLine);
var gotoLineNumber = 00;
bool needsFlag = false;
if (gotoLineEntry != null)
{
gotoLineNumber = gotoLineEntry.Location();
}
else
{
needsFlag = true;
}
// perform calculations with right operand
// add appropriate branch command
switch (comparator)
{
case "==":
_compiledCode.Add(Word.Build((int)EPC.Code.LOAD, leftEntry.Location()), _workingLineNumber++);
_compiledCode.Add(Word.Build((int)EPC.Code.SUBTRACT, rightEntry.Location()), _workingLineNumber++);
if (needsFlag)
{
_flags.Add(_workingLineNumber, intGotoLine);
}
_compiledCode.Add(Word.Build((int)EPC.Code.BRANCHZERO, gotoLineNumber), _workingLineNumber++);
break;
case "!=":
// check if greater than
_compiledCode.Add(Word.Build((int)EPC.Code.LOAD, rightEntry.Location()), _workingLineNumber++);
_compiledCode.Add(Word.Build((int)EPC.Code.SUBTRACT, leftEntry.Location()), _workingLineNumber++);
if (needsFlag)
{
_flags.Add(_workingLineNumber, intGotoLine);
}
_compiledCode.Add(Word.Build((int)EPC.Code.BRANCHNEG, gotoLineNumber), _workingLineNumber++);
// check if less than
_compiledCode.Add(Word.Build((int)EPC.Code.LOAD, leftEntry.Location()), _workingLineNumber++);
_compiledCode.Add(Word.Build((int)EPC.Code.SUBTRACT, rightEntry.Location()), _workingLineNumber++);
if (needsFlag)
{
_flags.Add(_workingLineNumber, intGotoLine);
}
_compiledCode.Add(Word.Build((int)EPC.Code.BRANCHNEG, gotoLineNumber), _workingLineNumber++);
break;
case "<":
_compiledCode.Add(Word.Build((int)EPC.Code.LOAD, leftEntry.Location()), _workingLineNumber++);
_compiledCode.Add(Word.Build((int)EPC.Code.SUBTRACT, rightEntry.Location()), _workingLineNumber++);
if (needsFlag)
{
_flags.Add(_workingLineNumber, intGotoLine);
}
_compiledCode.Add(Word.Build((int)EPC.Code.BRANCHNEG, gotoLineNumber), _workingLineNumber++);
break;
case ">":
_compiledCode.Add(Word.Build((int)EPC.Code.LOAD, rightEntry.Location()), _workingLineNumber++);
_compiledCode.Add(Word.Build((int)EPC.Code.SUBTRACT, leftEntry.Location()), _workingLineNumber++);
if (needsFlag)
{
_flags.Add(_workingLineNumber, intGotoLine);
}
_compiledCode.Add(Word.Build((int)EPC.Code.BRANCHNEG, gotoLineNumber), _workingLineNumber++);
break;
case "<=":
_compiledCode.Add(Word.Build((int)EPC.Code.LOAD, leftEntry.Location()), _workingLineNumber++);
_compiledCode.Add(Word.Build((int)EPC.Code.SUBTRACT, rightEntry.Location()), _workingLineNumber++);
if (needsFlag)
{
_flags.Add(_workingLineNumber, intGotoLine);
}
_compiledCode.Add(Word.Build((int)EPC.Code.BRANCHNEG, gotoLineNumber), _workingLineNumber++);
if (needsFlag)
{
_flags.Add(_workingLineNumber, intGotoLine);
}
_compiledCode.Add(Word.Build((int)EPC.Code.BRANCHZERO, gotoLineNumber), _workingLineNumber++);
break;
case ">=":
_compiledCode.Add(Word.Build((int)EPC.Code.LOAD, rightEntry.Location()), _workingLineNumber++);
_compiledCode.Add(Word.Build((int)EPC.Code.SUBTRACT, leftEntry.Location()), _workingLineNumber++);
if (needsFlag)
{
_flags.Add(_workingLineNumber, intGotoLine);
}
_compiledCode.Add(Word.Build((int)EPC.Code.BRANCHNEG, gotoLineNumber), _workingLineNumber++);
if (needsFlag)
{
_flags.Add(_workingLineNumber, intGotoLine);
}
_compiledCode.Add(Word.Build((int)EPC.Code.BRANCHZERO, gotoLineNumber), _workingLineNumber++);
break;
}
}
