Check relative branches for byte overflows

Author: craigthomas

cocoasm/statement.py

@@ -326,10 +326,18 @@ def fix_addresses(self, statements, this_index):
                 length = 1
                 for statement in statements[branch_index:this_index+1]:
                     length += statement.code_pkg.size
+
+                # Check for overflow errors if this is a short relative operation
+                if self.instruction.is_short_branch and length > 128:
+                    raise TranslationError(f"short relative branch cannot be less than -128 bytes", self)
                 self.code_pkg.additional = NumericValue(base_value - length, size_hint=size_hint)
             else:
                 for statement in statements[this_index+1:branch_index]:
                     length += statement.code_pkg.size
+
+                # Check for overflow errors if this is a short relative operation
+                if self.instruction.is_short_branch and length > 127:
+                    raise TranslationError(f"short relative branch cannot be more than 127 bytes", self)
                 self.code_pkg.additional = NumericValue(length, size_hint=size_hint)
             return
 

test/test_program.py

@@ -361,6 +361,36 @@ def test_translation_error_raised_on_bad_label(self):
             program.statements = [statement]
             program.translate_statements()
 
+    def test_translation_error_raised_on_short_branch_too_large_backward_branch(self):
+        statements = [
+            "  ORG $0600",
+            "START LDA #$01",
+        ]
+        for x in range(400):
+            statements.append("    LDA #$01")
+        statements.append("  BRA START")
+        program = Program()
+        with self.assertRaises(TranslationError) as context:
+            program.process(statements)
+
+        the_exception = context.exception
+        self.assertEqual("short relative branch cannot be less than -128 bytes", the_exception.value)
+
+    def test_translation_error_raised_on_short_branch_too_large_forward_branch(self):
+        statements = [
+            "  ORG $0600",
+            "START BRA THEEND",
+        ]
+        for x in range(400):
+            statements.append("    LDA #$01")
+        statements.append("THEEND  LDA #$01")
+        program = Program()
+        with self.assertRaises(TranslationError) as context:
+            program.process(statements)
+
+        the_exception = context.exception
+        self.assertEqual("short relative branch cannot be more than 127 bytes", the_exception.value)
+
     def test_get_binary_array_empty_if_no_statements(self):
         program = Program()
         self.assertEqual([], program.get_binary_array())