Improve Vectorisation

This MR fixes some bugs caused in the vectorisation

pystencils/backends/cbackend.py

@@ -787,18 +787,14 @@ class VectorizedCustomSympyPrinter(CustomSympyPrinter):
         else:
             exp = expr.exp
 
+        # TODO the printer should not have any intelligence like this.
+        # TODO To remove all of these cases the vectoriser needs to be reworked. See loop cutting
         if exp.is_integer and exp.is_number and 0 < exp < 8:
             return self._print(sp.Mul(*[expr.base] * exp, evaluate=False))
-        elif exp == -1:
-            return self.instruction_set['/'].format(one, self._print(expr.base), **self._kwargs)
         elif exp == 0.5:
             return root
         elif exp == -0.5:
             return self.instruction_set['/'].format(one, root, **self._kwargs)
-        elif exp.is_integer and exp.is_number and - 8 < exp < 0:
-            return self.instruction_set['/'].format(one,
-                                                    self._print(sp.Mul(*[expr.base] * (-exp), evaluate=False)),
-                                                    **self._kwargs)
         else:
             raise ValueError("Generic exponential not supported: " + str(expr))