Fix tuple/list wraparound failure.

Previously, if incrementing by the length failed to make the
index positive, this *incremented* index was passed in an attempt
to raise the correct error.

This fixes #1700.

Cython/Utility/ObjectHandling.c

@@ -282,9 +282,12 @@ static CYTHON_INLINE PyObject *__Pyx_GetItemInt_{{type}}_Fast(PyObject *o, Py_ss
                                                               CYTHON_NCP_UNUSED int wraparound,
                                                               CYTHON_NCP_UNUSED int boundscheck) {
 #if CYTHON_ASSUME_SAFE_MACROS && !CYTHON_AVOID_BORROWED_REFS
-    if (wraparound & unlikely(i < 0)) i += Py{{type}}_GET_SIZE(o);
-    if ((!boundscheck) || likely((0 <= i) & (i < Py{{type}}_GET_SIZE(o)))) {
-        PyObject *r = Py{{type}}_GET_ITEM(o, i);
+    Py_ssize_t wrapped_i = i;
+    if (wraparound & unlikely(i < 0)) {
+        wrapped_i += Py{{type}}_GET_SIZE(o);
+    }
+    if ((!boundscheck) || likely((0 <= wrapped_i) & (wrapped_i < Py{{type}}_GET_SIZE(o)))) {
+        PyObject *r = Py{{type}}_GET_ITEM(o, wrapped_i);
         Py_INCREF(r);
         return r;
     }

tests/run/index.pyx

@@ -29,6 +29,9 @@ def index_tuple(tuple t, int i):
     >>> index_tuple((1,1,2,3,5), 100)
     Traceback (most recent call last):
     IndexError: tuple index out of range
+    >>> index_tuple((1,1,2,3,5), -7)
+    Traceback (most recent call last):
+    IndexError: tuple index out of range
     >>> index_tuple(None, 0)
     Traceback (most recent call last):
     TypeError: 'NoneType' object is not subscriptable
@@ -46,6 +49,9 @@ def index_list(list L, int i):
     >>> index_list([2,3,5,7,11,13,17,19], 100)
     Traceback (most recent call last):
     IndexError: list index out of range
+    >>> index_list([2,3,5,7,11,13,17,19], -10)
+    Traceback (most recent call last):
+    IndexError: list index out of range
     >>> index_list(None, 0)
     Traceback (most recent call last):
     TypeError: 'NoneType' object is not subscriptable