Implement OperandStack for Runtime

runtime/Makefile

@@ -1,5 +1,10 @@
 CC=gcc
 CFLAGS=-I.
+DEPS=OperandStack.h
+OBJ=OperandStack.o salruntime.o
 
-salruntime: salruntime.c
+%.o: %.c $(DEPS)
+	$(CC) -c -o $@ $< $(CFLAGS)
+
+salruntime: $(OBJ)
 	$(CC) -o $@ $^ $(CFLAGS)

runtime/OperandStack.c

@@ -0,0 +1,29 @@
+#include "OperandStack.h"
+
+int OStackSize(OperandStack* stack) {
+    return stack->top;
+}
+
+int OStackPush(OperandStack* stack, int operand) {
+    if (OStackSize(stack) >= TYPE_STACK_SIZE) {
+        // Stack overflow
+        return -1;
+    }
+
+    stack->operands[stack->top] = operand;
+    stack->top++;
+
+    return 0;
+}
+
+int OStackPop(OperandStack* stack, int* result) {
+    if (OStackSize(stack) == 0) {
+        // Stack underflow
+        return -1;
+    }
+
+    *result = stack->operands[stack->top - 1];
+    stack->top--;
+
+    return 0;
+}

runtime/OperandStack.h

@@ -0,0 +1,17 @@
+#ifndef OPERAND_STACK
+#define OPERAND_STACK
+
+#define TYPE_STACK_SIZE 32
+
+typedef struct OperandStack {
+    int top;
+    int operands[TYPE_STACK_SIZE];
+} OperandStack;
+
+int OStackSize(OperandStack* stack);
+
+int OStackPush(OperandStack* stack, int operand);
+
+int OStackPop(OperandStack* stack, int* result);
+
+#endif