1 files changed, 183 insertions, 8 deletions

diff --git a/Objects/sliceobject.c b/Objects/sliceobject.c
index 1593335263..52f1c89ded 100644
--- a/Objects/sliceobject.c
+++ b/Objects/sliceobject.c
@@ -299,23 +299,198 @@ static PyMemberDef slice_members[] = {
     {0}
 };
 
+/* Helper function to convert a slice argument to a PyLong, and raise TypeError
+   with a suitable message on failure. */
+
 static PyObject*
-slice_indices(PySliceObject* self, PyObject* len)
+evaluate_slice_index(PyObject *v)
 {
-    Py_ssize_t ilen, start, stop, step, slicelength;
+    if (PyIndex_Check(v)) {
+        return PyNumber_Index(v);
+    }
+    else {
+        PyErr_SetString(PyExc_TypeError,
+                        "slice indices must be integers or "
+                        "None or have an __index__ method");
+        return NULL;
+    }
+}
 
-    ilen = PyNumber_AsSsize_t(len, PyExc_OverflowError);
+/* Compute slice indices given a slice and length.  Return -1 on failure.  Used
+   by slice.indices and rangeobject slicing.  Assumes that `len` is a
+   nonnegative instance of PyLong. */
 
-    if (ilen == -1 && PyErr_Occurred()) {
-        return NULL;
+int
+_PySlice_GetLongIndices(PySliceObject *self, PyObject *length,
+                        PyObject **start_ptr, PyObject **stop_ptr,
+                        PyObject **step_ptr)
+{
+    PyObject *start=NULL, *stop=NULL, *step=NULL;
+    PyObject *upper=NULL, *lower=NULL;
+    int step_is_negative, cmp_result;
+
+    /* Convert step to an integer; raise for zero step. */
+    if (self->step == Py_None) {
+        step = PyLong_FromLong(1L);
+        if (step == NULL)
+            goto error;
+        step_is_negative = 0;
+    }
+    else {
+        int step_sign;
+        step = evaluate_slice_index(self->step);
+        if (step == NULL)
+            goto error;
+        step_sign = _PyLong_Sign(step);
+        if (step_sign == 0) {
+            PyErr_SetString(PyExc_ValueError,
+                            "slice step cannot be zero");
+            goto error;
+        }
+        step_is_negative = step_sign < 0;
+    }
+
+    /* Find lower and upper bounds for start and stop. */
+    if (step_is_negative) {
+        lower = PyLong_FromLong(-1L);
+        if (lower == NULL)
+            goto error;
+
+        upper = PyNumber_Add(length, lower);
+        if (upper == NULL)
+            goto error;
+    }
+    else {
+        lower = PyLong_FromLong(0L);
+        if (lower == NULL)
+            goto error;
+
+        upper = length;
+        Py_INCREF(upper);
     }
 
-    if (PySlice_GetIndicesEx((PyObject*)self, ilen, &start, &stop,
-                             &step, &slicelength) < 0) {
+    /* Compute start. */
+    if (self->start == Py_None) {
+        start = step_is_negative ? upper : lower;
+        Py_INCREF(start);
+    }
+    else {
+        start = evaluate_slice_index(self->start);
+        if (start == NULL)
+            goto error;
+
+        if (_PyLong_Sign(start) < 0) {
+            /* start += length */
+            PyObject *tmp = PyNumber_Add(start, length);
+            Py_DECREF(start);
+            start = tmp;
+            if (start == NULL)
+                goto error;
+
+            cmp_result = PyObject_RichCompareBool(start, lower, Py_LT);
+            if (cmp_result < 0)
+                goto error;
+            if (cmp_result) {
+                Py_INCREF(lower);
+                Py_DECREF(start);
+                start = lower;
+            }
+        }
+        else {
+            cmp_result = PyObject_RichCompareBool(start, upper, Py_GT);
+            if (cmp_result < 0)
+                goto error;
+            if (cmp_result) {
+                Py_INCREF(upper);
+                Py_DECREF(start);
+                start = upper;
+            }
+        }
+    }
+
+    /* Compute stop. */
+    if (self->stop == Py_None) {
+        stop = step_is_negative ? lower : upper;
+        Py_INCREF(stop);
+    }
+    else {
+        stop = evaluate_slice_index(self->stop);
+        if (stop == NULL)
+            goto error;
+
+        if (_PyLong_Sign(stop) < 0) {
+            /* stop += length */
+            PyObject *tmp = PyNumber_Add(stop, length);
+            Py_DECREF(stop);
+            stop = tmp;
+            if (stop == NULL)
+                goto error;
+
+            cmp_result = PyObject_RichCompareBool(stop, lower, Py_LT);
+            if (cmp_result < 0)
+                goto error;
+            if (cmp_result) {
+                Py_INCREF(lower);
+                Py_DECREF(stop);
+                stop = lower;
+            }
+        }
+        else {
+            cmp_result = PyObject_RichCompareBool(stop, upper, Py_GT);
+            if (cmp_result < 0)
+                goto error;
+            if (cmp_result) {
+                Py_INCREF(upper);
+                Py_DECREF(stop);
+                stop = upper;
+            }
+        }
+    }
+
+    *start_ptr = start;
+    *stop_ptr = stop;
+    *step_ptr = step;
+    Py_DECREF(upper);
+    Py_DECREF(lower);
+    return 0;
+
+  error:
+    *start_ptr = *stop_ptr = *step_ptr = NULL;
+    Py_XDECREF(start);
+    Py_XDECREF(stop);
+    Py_XDECREF(step);
+    Py_XDECREF(upper);
+    Py_XDECREF(lower);
+    return -1;
+}
+
+/* Implementation of slice.indices. */
+
+static PyObject*
+slice_indices(PySliceObject* self, PyObject* len)
+{
+    PyObject *start, *stop, *step;
+    PyObject *length;
+    int error;
+
+    /* Convert length to an integer if necessary; raise for negative length. */
+    length = PyNumber_Index(len);
+    if (length == NULL)
+        return NULL;
+
+    if (_PyLong_Sign(length) < 0) {
+        PyErr_SetString(PyExc_ValueError,
+                        "length should not be negative");
+        Py_DECREF(length);
         return NULL;
     }
 
-    return Py_BuildValue("(nnn)", start, stop, step);
+    error = _PySlice_GetLongIndices(self, length, &start, &stop, &step);
+    Py_DECREF(length);
+    if (error == -1)
+        return NULL;
+    else
+        return Py_BuildValue("(NNN)", start, stop, step);
 }
 
 PyDoc_STRVAR(slice_indices_doc,