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#include "py27_backports.h"
// Provide implementations from python 2.7.15 as backports
int
_PySlice_Unpack(PyObject *_r,
Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t *step)
{
PySliceObject *r = (PySliceObject *)_r;
/* this is harder to get right than you might think */
assert(PY_SSIZE_T_MIN + 1 <= -PY_SSIZE_T_MAX);
if (r->step == Py_None) {
*step = 1;
}
else {
if (!_PyEval_SliceIndex(r->step, step)) return -1;
if (*step == 0) {
PyErr_SetString(PyExc_ValueError,
"slice step cannot be zero");
return -1;
}
/* Here *step might be -PY_SSIZE_T_MAX-1; in this case we replace it
* with -PY_SSIZE_T_MAX. This doesn't affect the semantics, and it
* guards against later undefined behaviour resulting from code that
* does "step = -step" as part of a slice reversal.
*/
if (*step < -PY_SSIZE_T_MAX)
*step = -PY_SSIZE_T_MAX;
}
if (r->start == Py_None) {
*start = *step < 0 ? PY_SSIZE_T_MAX : 0;
}
else {
if (!_PyEval_SliceIndex(r->start, start)) return -1;
}
if (r->stop == Py_None) {
*stop = *step < 0 ? PY_SSIZE_T_MIN : PY_SSIZE_T_MAX;
}
else {
if (!_PyEval_SliceIndex(r->stop, stop)) return -1;
}
return 0;
}
Py_ssize_t
_PySlice_AdjustIndices(Py_ssize_t length,
Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t step)
{
/* this is harder to get right than you might think */
assert(step != 0);
assert(step >= -PY_SSIZE_T_MAX);
if (*start < 0) {
*start += length;
if (*start < 0) {
*start = (step < 0) ? -1 : 0;
}
}
else if (*start >= length) {
*start = (step < 0) ? length - 1 : length;
}
if (*stop < 0) {
*stop += length;
if (*stop < 0) {
*stop = (step < 0) ? -1 : 0;
}
}
else if (*stop >= length) {
*stop = (step < 0) ? length - 1 : length;
}
if (step < 0) {
if (*stop < *start) {
return (*start - *stop - 1) / (-step) + 1;
}
}
else {
if (*start < *stop) {
return (*stop - *start - 1) / step + 1;
}
}
return 0;
}
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