mirror of https://github.com/python/cpython
Issue #16451: Refactor to remove duplication between range and slice in slice index computations.
This commit is contained in:
Mark Dickinson
parent
c3afba104a
commit
ffdb2c21b3
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@ -34,6 +34,9 @@ PyAPI_FUNC(PyObject *) PySlice_New(PyObject* start, PyObject* stop,
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PyObject* step);
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#ifndef Py_LIMITED_API
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PyAPI_FUNC(PyObject *) _PySlice_FromIndices(Py_ssize_t start, Py_ssize_t stop);
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PyAPI_FUNC(int) _PySlice_GetLongIndices(PySliceObject *self, PyObject *length,
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PyObject **start_ptr, PyObject **stop_ptr,
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PyObject **step_ptr);
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#endif
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PyAPI_FUNC(int) PySlice_GetIndices(PyObject *r, Py_ssize_t length,
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Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t *step);
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@ -318,195 +318,6 @@ range_item(rangeobject *r, Py_ssize_t i)
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return res;
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}
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/* Additional helpers, since the standard slice helpers
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* all clip to PY_SSIZE_T_MAX
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*/
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/* Replace _PyEval_SliceIndex */
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static PyObject *
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compute_slice_element(PyObject *obj)
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{
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PyObject *result = NULL;
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if (obj != NULL) {
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if (PyIndex_Check(obj)) {
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result = PyNumber_Index(obj);
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}
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else {
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PyErr_SetString(PyExc_TypeError,
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"slice indices must be integers or "
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"None or have an __index__ method");
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}
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}
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return result;
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}
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/* Replace PySlice_GetIndicesEx
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* Result indicates whether or not the slice is empty
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* (-1 = error, 0 = empty slice, 1 = slice contains elements)
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*/
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static int
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compute_slice_indices(rangeobject *r, PySliceObject *slice,
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PyObject **start, PyObject **stop, PyObject **step)
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{
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int cmp_result, has_elements;
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Py_ssize_t clamped_step = 0;
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PyObject *zero = NULL, *one = NULL, *neg_one = NULL, *candidate = NULL;
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PyObject *tmp_start = NULL, *tmp_stop = NULL, *tmp_step = NULL;
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zero = PyLong_FromLong(0);
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if (zero == NULL) goto Fail;
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one = PyLong_FromLong(1);
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if (one == NULL) goto Fail;
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neg_one = PyLong_FromLong(-1);
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if (neg_one == NULL) goto Fail;
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/* Calculate step value */
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if (slice->step == Py_None) {
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clamped_step = 1;
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tmp_step = one;
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Py_INCREF(tmp_step);
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} else {
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if (!_PyEval_SliceIndex(slice->step, &clamped_step)) goto Fail;
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if (clamped_step == 0) {
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PyErr_SetString(PyExc_ValueError,
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"slice step cannot be zero");
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goto Fail;
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}
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tmp_step = compute_slice_element(slice->step);
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if (tmp_step == NULL) goto Fail;
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}
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/* Calculate start value */
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if (slice->start == Py_None) {
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if (clamped_step < 0) {
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tmp_start = PyNumber_Subtract(r->length, one);
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if (tmp_start == NULL) goto Fail;
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} else {
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tmp_start = zero;
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Py_INCREF(tmp_start);
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}
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} else {
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candidate = compute_slice_element(slice->start);
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if (candidate == NULL) goto Fail;
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cmp_result = PyObject_RichCompareBool(candidate, zero, Py_LT);
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if (cmp_result == -1) goto Fail;
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if (cmp_result) {
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/* candidate < 0 */
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tmp_start = PyNumber_Add(r->length, candidate);
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if (tmp_start == NULL) goto Fail;
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Py_CLEAR(candidate);
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} else {
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/* candidate >= 0 */
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tmp_start = candidate;
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candidate = NULL;
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}
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cmp_result = PyObject_RichCompareBool(tmp_start, zero, Py_LT);
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if (cmp_result == -1) goto Fail;
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if (cmp_result) {
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/* tmp_start < 0 */
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Py_CLEAR(tmp_start);
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if (clamped_step < 0) {
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tmp_start = neg_one;
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} else {
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tmp_start = zero;
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}
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Py_INCREF(tmp_start);
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} else {
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/* tmp_start >= 0 */
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cmp_result = PyObject_RichCompareBool(tmp_start, r->length, Py_GE);
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if (cmp_result == -1) goto Fail;
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if (cmp_result) {
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/* tmp_start >= r->length */
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Py_CLEAR(tmp_start);
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if (clamped_step < 0) {
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tmp_start = PyNumber_Subtract(r->length, one);
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if (tmp_start == NULL) goto Fail;
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} else {
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tmp_start = r->length;
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Py_INCREF(tmp_start);
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}
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}
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}
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}
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/* Calculate stop value */
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if (slice->stop == Py_None) {
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if (clamped_step < 0) {
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tmp_stop = neg_one;
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} else {
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tmp_stop = r->length;
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}
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Py_INCREF(tmp_stop);
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} else {
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candidate = compute_slice_element(slice->stop);
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if (candidate == NULL) goto Fail;
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cmp_result = PyObject_RichCompareBool(candidate, zero, Py_LT);
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if (cmp_result == -1) goto Fail;
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if (cmp_result) {
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/* candidate < 0 */
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tmp_stop = PyNumber_Add(r->length, candidate);
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if (tmp_stop == NULL) goto Fail;
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Py_CLEAR(candidate);
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} else {
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/* candidate >= 0 */
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tmp_stop = candidate;
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candidate = NULL;
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}
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cmp_result = PyObject_RichCompareBool(tmp_stop, zero, Py_LT);
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if (cmp_result == -1) goto Fail;
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if (cmp_result) {
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/* tmp_stop < 0 */
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Py_CLEAR(tmp_stop);
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if (clamped_step < 0) {
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tmp_stop = neg_one;
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} else {
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tmp_stop = zero;
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}
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Py_INCREF(tmp_stop);
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} else {
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/* tmp_stop >= 0 */
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cmp_result = PyObject_RichCompareBool(tmp_stop, r->length, Py_GE);
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if (cmp_result == -1) goto Fail;
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if (cmp_result) {
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/* tmp_stop >= r->length */
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Py_CLEAR(tmp_stop);
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if (clamped_step < 0) {
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tmp_stop = PyNumber_Subtract(r->length, one);
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if (tmp_stop == NULL) goto Fail;
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} else {
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tmp_stop = r->length;
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Py_INCREF(tmp_stop);
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}
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}
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}
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}
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/* Check if the slice is empty or not */
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if (clamped_step < 0) {
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has_elements = PyObject_RichCompareBool(tmp_start, tmp_stop, Py_GT);
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} else {
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has_elements = PyObject_RichCompareBool(tmp_start, tmp_stop, Py_LT);
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}
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if (has_elements == -1) goto Fail;
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*start = tmp_start;
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*stop = tmp_stop;
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*step = tmp_step;
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Py_DECREF(neg_one);
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Py_DECREF(one);
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Py_DECREF(zero);
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return has_elements;
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Fail:
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Py_XDECREF(tmp_start);
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Py_XDECREF(tmp_stop);
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Py_XDECREF(tmp_step);
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Py_XDECREF(candidate);
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Py_XDECREF(neg_one);
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Py_XDECREF(one);
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Py_XDECREF(zero);
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return -1;
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}
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static PyObject *
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compute_slice(rangeobject *r, PyObject *_slice)
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{
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@ -514,10 +325,11 @@ compute_slice(rangeobject *r, PyObject *_slice)
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rangeobject *result;
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PyObject *start = NULL, *stop = NULL, *step = NULL;
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PyObject *substart = NULL, *substop = NULL, *substep = NULL;
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int has_elements;
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int error;
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has_elements = compute_slice_indices(r, slice, &start, &stop, &step);
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if (has_elements == -1) return NULL;
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error = _PySlice_GetLongIndices(slice, r->length, &start, &stop, &step);
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if (error == -1)
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return NULL;
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substep = PyNumber_Multiply(r->step, step);
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if (substep == NULL) goto fail;
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@ -527,13 +339,8 @@ compute_slice(rangeobject *r, PyObject *_slice)
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if (substart == NULL) goto fail;
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Py_CLEAR(start);
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if (has_elements) {
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substop = compute_item(r, stop);
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if (substop == NULL) goto fail;
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} else {
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substop = substart;
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Py_INCREF(substop);
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}
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Py_CLEAR(stop);
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result = make_range_object(Py_TYPE(r), substart, substop, substep);
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@ -316,57 +316,41 @@ evaluate_slice_index(PyObject *v)
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}
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}
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/* Implementation of slice.indices. */
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/* Compute slice indices given a slice and length. Return -1 on failure. Used
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by slice.indices and rangeobject slicing. Assumes that `len` is a
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nonnegative instance of PyLong. */
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static PyObject*
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slice_indices(PySliceObject* self, PyObject* len)
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int
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_PySlice_GetLongIndices(PySliceObject *self, PyObject *length,
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PyObject **start_ptr, PyObject **stop_ptr,
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PyObject **step_ptr)
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{
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PyObject *start=NULL, *stop=NULL, *step=NULL;
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PyObject *length=NULL, *upper=NULL, *lower=NULL, *zero=NULL;
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int step_is_negative, cmp;
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PyObject *upper=NULL, *lower=NULL;
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int step_is_negative, cmp_result;
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zero = PyLong_FromLong(0L);
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if (zero == NULL)
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return NULL;
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/* Compute step and length as integers. */
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length = PyNumber_Index(len);
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if (length == NULL)
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goto error;
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if (self->step == Py_None)
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/* Convert step to an integer; raise for zero step. */
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if (self->step == Py_None) {
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step = PyLong_FromLong(1L);
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else
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if (step == NULL)
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goto error;
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step_is_negative = 0;
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}
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else {
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int step_sign;
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step = evaluate_slice_index(self->step);
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if (step == NULL)
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goto error;
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/* Raise ValueError for negative length or zero step. */
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cmp = PyObject_RichCompareBool(length, zero, Py_LT);
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if (cmp < 0) {
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goto error;
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}
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if (cmp) {
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PyErr_SetString(PyExc_ValueError,
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"length should not be negative");
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goto error;
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}
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cmp = PyObject_RichCompareBool(step, zero, Py_EQ);
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if (cmp < 0) {
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goto error;
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}
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if (cmp) {
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step_sign = _PyLong_Sign(step);
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if (step_sign == 0) {
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PyErr_SetString(PyExc_ValueError,
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"slice step cannot be zero");
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goto error;
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}
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step_is_negative = step_sign < 0;
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}
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/* Find lower and upper bounds for start and stop. */
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step_is_negative = PyObject_RichCompareBool(step, zero, Py_LT);
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if (step_is_negative < 0) {
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goto error;
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}
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if (step_is_negative) {
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lower = PyLong_FromLong(-1L);
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if (lower == NULL)
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@ -377,8 +361,10 @@ slice_indices(PySliceObject* self, PyObject* len)
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goto error;
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}
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else {
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lower = zero;
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Py_INCREF(lower);
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lower = PyLong_FromLong(0L);
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if (lower == NULL)
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goto error;
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upper = length;
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Py_INCREF(upper);
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}
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@ -393,10 +379,7 @@ slice_indices(PySliceObject* self, PyObject* len)
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if (start == NULL)
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goto error;
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cmp = PyObject_RichCompareBool(start, zero, Py_LT);
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if (cmp < 0)
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goto error;
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if (cmp) {
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if (_PyLong_Sign(start) < 0) {
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/* start += length */
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PyObject *tmp = PyNumber_Add(start, length);
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Py_DECREF(start);
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@ -404,20 +387,20 @@ slice_indices(PySliceObject* self, PyObject* len)
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if (start == NULL)
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goto error;
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cmp = PyObject_RichCompareBool(start, lower, Py_LT);
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if (cmp < 0)
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cmp_result = PyObject_RichCompareBool(start, lower, Py_LT);
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if (cmp_result < 0)
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goto error;
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if (cmp) {
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if (cmp_result) {
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Py_INCREF(lower);
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Py_DECREF(start);
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start = lower;
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}
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}
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else {
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cmp = PyObject_RichCompareBool(start, upper, Py_GT);
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if (cmp < 0)
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cmp_result = PyObject_RichCompareBool(start, upper, Py_GT);
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if (cmp_result < 0)
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goto error;
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if (cmp) {
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if (cmp_result) {
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Py_INCREF(upper);
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Py_DECREF(start);
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start = upper;
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@ -435,10 +418,7 @@ slice_indices(PySliceObject* self, PyObject* len)
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if (stop == NULL)
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goto error;
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cmp = PyObject_RichCompareBool(stop, zero, Py_LT);
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if (cmp < 0)
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goto error;
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if (cmp) {
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if (_PyLong_Sign(stop) < 0) {
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/* stop += length */
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PyObject *tmp = PyNumber_Add(stop, length);
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Py_DECREF(stop);
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@ -446,20 +426,20 @@ slice_indices(PySliceObject* self, PyObject* len)
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if (stop == NULL)
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goto error;
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cmp = PyObject_RichCompareBool(stop, lower, Py_LT);
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if (cmp < 0)
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cmp_result = PyObject_RichCompareBool(stop, lower, Py_LT);
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if (cmp_result < 0)
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goto error;
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if (cmp) {
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if (cmp_result) {
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Py_INCREF(lower);
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Py_DECREF(stop);
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stop = lower;
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}
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}
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else {
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cmp = PyObject_RichCompareBool(stop, upper, Py_GT);
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if (cmp < 0)
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cmp_result = PyObject_RichCompareBool(stop, upper, Py_GT);
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if (cmp_result < 0)
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goto error;
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if (cmp) {
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if (cmp_result) {
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Py_INCREF(upper);
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Py_DECREF(stop);
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stop = upper;
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@ -467,23 +447,51 @@ slice_indices(PySliceObject* self, PyObject* len)
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}
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}
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*start_ptr = start;
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*stop_ptr = stop;
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*step_ptr = step;
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Py_DECREF(upper);
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Py_DECREF(lower);
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Py_DECREF(length);
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Py_DECREF(zero);
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return Py_BuildValue("(NNN)", start, stop, step);
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return 0;
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error:
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*start_ptr = *stop_ptr = *step_ptr = NULL;
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Py_XDECREF(start);
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Py_XDECREF(stop);
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Py_XDECREF(step);
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Py_XDECREF(upper);
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Py_XDECREF(lower);
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Py_XDECREF(length);
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Py_XDECREF(zero);
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return NULL;
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return -1;
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}
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/* Implementation of slice.indices. */
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static PyObject*
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slice_indices(PySliceObject* self, PyObject* len)
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{
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PyObject *start, *stop, *step;
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PyObject *length;
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int error;
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/* Convert length to an integer if necessary; raise for negative length. */
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length = PyNumber_Index(len);
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if (length == NULL)
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return NULL;
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if (_PyLong_Sign(length) < 0) {
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PyErr_SetString(PyExc_ValueError,
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"length should not be negative");
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Py_DECREF(length);
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return NULL;
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}
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error = _PySlice_GetLongIndices(self, length, &start, &stop, &step);
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Py_DECREF(length);
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if (error == -1)
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return NULL;
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else
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return Py_BuildValue("(NNN)", start, stop, step);
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}
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PyDoc_STRVAR(slice_indices_doc,
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"S.indices(len) -> (start, stop, stride)\n\
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