Use Registers for finding next free register in parseBinaryOp

1 files changed, 25 insertions, 11 deletions

diff --git a/pp2cc.py b/pp2cc.py
index a73189d..a3597aa 100755
--- a/pp2cc.py
+++ b/pp2cc.py
@@ -34,14 +34,24 @@ class Registers(object):
         self.registers = {}
         for reg in range(0, 8):
             self.registers[str(reg)] = False
-    def alloc(self):
+    def alloc(self, register=None):
         """Retrieves a register which is marked unused and marks it as in use"""
+        # if a register was explicitly requested
+        if register:
+            if not self.is_register(register):
+                raise RuntimeError("'{}' is not a register".format(register))
+            register = register[1]
+            if self.registers[register]:
+                raise RuntimeError("Register 'R{}' is already in use".format(register))
         for register in range(0, 6):
+            register = str(register)
             # find a free register
             if not self.registers[register]:
-                self.registers[register] = True
-                return "R" + register
-        raise RuntimeError("No free registers are available")
+                break
+        else:
+            raise RuntimeError("No free registers are available")
+        self.registers[register] = True
+        return "R" + register
     def free(self, register):
         """Marks a register as unused
 
@@ -51,7 +61,7 @@ class Registers(object):
         """
         # remove leading R
         register = register[1:]
-        if self.registers[register]:
+        if register in self.registers:
             self.registers[register] = False;
         else:
             raise RuntimeError("free() of unused register")
@@ -68,10 +78,13 @@ class Registers(object):
         # retieve the first element before the next space, e.g. R0
         text = text.lstrip(" ").split(" ", 1)[0]
         # is it a register?
-        if len(text) == 2 and text[0] == "R" and text[1] in self.registers:
+        if self.is_register(text):
             return text
         # out of luck
         return None
+    def is_register(self, text):
+        """Returns True if text is a register, false otherwise"""
+        return len(text) == 2 and text[0] == "R" and text[1] in self.registers
     def get_instruction(self, text):
         """Retrieve the instruction from text skipping labels and comments"""
         text = text.strip()
@@ -478,11 +491,12 @@ class Parse(object):
             operand = reg_second
 
             # since we use the stack for calculations, we can use less
-            # registers: R0 and R1
-            if reg_second == "R0":
-                reg_first = "R1"
-            else:
-                reg_first = "R0"
+            # registers (2). Use the Registers class for determining the next
+            # free register
+            self.registers.alloc(reg_second)
+            reg_first = self.registers.alloc()
+            self.registers.free(reg_second)
+            self.registers.free(reg_first)
             # put the data back in the free register
             lines.append(self.asm.pull(reg_first))