Merge pull request #352 from BigFav/reverse_range_optimize

Optimized reversed range with constant negative steps.

Cython/Compiler/Optimize.py

@@ -661,24 +661,31 @@ class IterationTransform(Visitor.EnvTransform):
         if reversed:
             bound1, bound2 = bound2, bound1
             if step_value < 0:
-                if step_value != -1:
-                    # FIXME: not currently supported
-                    return node
                 step_value = -step_value
-            if step_value != 1:
+                if step_value != 1:
+                    begin_value = bound2.constant_result
+                    end_value = bound1.constant_result
+                    if isinstance(begin_value, (int, long)) and isinstance(end_value, (int, long)):
+                        bound1_value = begin_value - step_value * ((begin_value - end_value - 1) // step_value) - 1
+                        bound1 = ExprNodes.IntNode(
+                            bound1.pos, value=str(bound1_value), constant_result=bound1_value,
+                            type=PyrexTypes.spanning_type(bound1.type, bound2.type))
+                    else:
+                        # FIXME: Optimize when variable is in range (e.g. reversed(range(x, y, -3)))
+                        return node
+            elif step_value != 1:
                 begin_value = bound1.constant_result
                 end_value = bound2.constant_result
                 if isinstance(begin_value, (int, long)) and isinstance(end_value, (int, long)):
-                    bound1_value = step_value * ((begin_value - end_value - 1) // step_value) + end_value + 1
+                    bound1_value = end_value + step_value * ((begin_value - end_value - 1) // step_value) + 1
                     bound1 = ExprNodes.IntNode(
                         bound1.pos, value=str(bound1_value), constant_result=bound1_value,
                         type=PyrexTypes.spanning_type(bound1.type, bound2.type))
                 else:
                     # FIXME: Optimize when variable is in range (e.g. reversed(range(x, y, 3)))
                     return node
-        else:
-            if step_value < 0:
-                step_value = -step_value
+        elif step_value < 0:
+            step_value = -step_value
 
         step.value = str(step_value)
         step.constant_result = step_value