From a6fa6da5de8252a205e000dd7acc2589735aa55c Mon Sep 17 00:00:00 2001
From: ymherklotz <ymherklotz@gmail.com>
Date: Fri, 10 Mar 2017 19:57:46 +0000
Subject: Can do simple add and subtract

---
 c_compiler/src/expression.cpp | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

(limited to 'c_compiler/src/expression.cpp')

diff --git a/c_compiler/src/expression.cpp b/c_compiler/src/expression.cpp
index 8935e37..fb5b62b 100644
--- a/c_compiler/src/expression.cpp
+++ b/c_compiler/src/expression.cpp
@@ -5,17 +5,25 @@
 
 // Expression definition
 
+// There are no values to delete so it is just empty
 Expression::~Expression()
 {}
 
 void Expression::print() const
-{}
+{
+    std::cerr << "This expression has not been implemented yet" << std::endl;
+}
 
 void Expression::printxml() const
-{}
+{
+    // Does nothing as I do not want it to appear in the xml output
+}
 
 int32_t Expression::getPostfixStackPosition(VariableStackBindings bindings) const
 {
+    std::cerr << "Error: Can't call 'getPostfixStackPosition(VariableStackBindings " <<
+	"bindings)' on this type of expression" << std::endl;
+    (void)bindings;
     return -1;
 }
 
@@ -26,6 +34,7 @@ OperationExpression::OperationExpression(Expression* _lhs, Expression* _rhs)
     : lhs(_lhs), rhs(_rhs)
 {}
 
+// deletes the two member variables that have been initialized
 OperationExpression::~OperationExpression()
 {
     delete lhs;
@@ -41,30 +50,41 @@ AssignmentExpression::AssignmentExpression(Expression* _lhs, Expression* _rhs)
 
 VariableStackBindings AssignmentExpression::printasm(VariableStackBindings bindings) const
 {
+    // the lhs is forced to have a stack position due to it being a function, array or other type of variable
     int32_t store_stack_position = lhs->getPostfixStackPosition(bindings);
     rhs->printasm(bindings);
 
+    // we are assigning so we don't have to evaluate the lhs as it will be overwritten anyways
     std::cout << "\tsw\t$2," << store_stack_position << "($fp)" << std::endl;
-								   
     return bindings;
 }
 
 
 // Additive Expression definition
 
-AdditiveExpression::AdditiveExpression(Expression* _lhs, const std::string& _operand, Expression* _rhs)
-    : OperationExpression(_lhs, _rhs), operand(_operand)
+AdditiveExpression::AdditiveExpression(Expression* _lhs, const std::string& _operation, Expression* _rhs)
+    : OperationExpression(_lhs, _rhs), operation(_operation)
 {}
 
 VariableStackBindings AdditiveExpression::printasm(VariableStackBindings bindings) const
 {
     rhs->printasm(bindings);
 
+    // move the rhs out of the way to be able to evaluate the lhs
     std::cout << "\tmove\t$3,$2" << std::endl;
 
     lhs->printasm(bindings);
 
-    std::cout << "\tadd\t$2,$2,$3" << std::endl;
+    // then perform the right operation
+    
+    // currently using signed and sub because I only have signed numbers implemented
+    // must update this as I add more types
+    if(operation == "+")
+	std::cout << "\tadd\t$2,$2,$3" << std::endl;
+    else if(operation == "-")
+	std::cout << "\tsub\t$2,$2,$3" << std::endl;
+    else
+	std::cerr << "Don't recognize symbol: '" << operation << "'" << std::endl;
 
     return bindings;
 }
@@ -106,6 +126,7 @@ Constant::Constant(const int32_t& constant)
 
 VariableStackBindings Constant::printasm(VariableStackBindings bindings) const
 {
+    // constant only has to load to $2 because the other expression will take care of the rest
     std::cout << "\tli\t$2," << m_constant << std::endl;
 
     return bindings;
-- 
cgit