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Issue #16451: Refactor to remove duplication between range and slice in slice index computations.

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This commit is contained in:
Mark Dickinson 2012-11-17 19:18:10 +00:00
parent c3afba104a
commit ffdb2c21b3
3 changed files with 87 additions and 269 deletions
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148
Objects/sliceobject.c
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@ -316,57 +316,41 @@ evaluate_slice_index(PyObject *v)
}
}
/* Implementation of slice.indices. */
/* 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. */
static PyObject*
slice_indices(PySliceObject* self, PyObject* len)
int
_PySlice_GetLongIndices(PySliceObject *self, PyObject *length,
PyObject **start_ptr, PyObject **stop_ptr,
PyObject **step_ptr)
{
PyObject *start=NULL, *stop=NULL, *step=NULL;
PyObject *length=NULL, *upper=NULL, *lower=NULL, *zero=NULL;
int step_is_negative, cmp;
PyObject *upper=NULL, *lower=NULL;
int step_is_negative, cmp_result;
zero = PyLong_FromLong(0L);
if (zero == NULL)
return NULL;
/* Compute step and length as integers. */
length = PyNumber_Index(len);
if (length == NULL)
goto error;
if (self->step == Py_None)
/* Convert step to an integer; raise for zero step. */
if (self->step == Py_None) {
step = PyLong_FromLong(1L);
else
if (step == NULL)
goto error;
step_is_negative = 0;
}
else {
int step_sign;
step = evaluate_slice_index(self->step);
if (step == NULL)
goto error;
/* Raise ValueError for negative length or zero step. */
cmp = PyObject_RichCompareBool(length, zero, Py_LT);
if (cmp < 0) {
goto error;
}
if (cmp) {
PyErr_SetString(PyExc_ValueError,
"length should not be negative");
goto error;
}
cmp = PyObject_RichCompareBool(step, zero, Py_EQ);
if (cmp < 0) {
goto error;
}
if (cmp) {
PyErr_SetString(PyExc_ValueError,
"slice step cannot be zero");
goto error;
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. */
step_is_negative = PyObject_RichCompareBool(step, zero, Py_LT);
if (step_is_negative < 0) {
goto error;
}
if (step_is_negative) {
lower = PyLong_FromLong(-1L);
if (lower == NULL)
@ -377,8 +361,10 @@ slice_indices(PySliceObject* self, PyObject* len)
goto error;
}
else {
lower = zero;
Py_INCREF(lower);
lower = PyLong_FromLong(0L);
if (lower == NULL)
goto error;
upper = length;
Py_INCREF(upper);
}
@ -393,10 +379,7 @@ slice_indices(PySliceObject* self, PyObject* len)
if (start == NULL)
goto error;
cmp = PyObject_RichCompareBool(start, zero, Py_LT);
if (cmp < 0)
goto error;
if (cmp) {
if (_PyLong_Sign(start) < 0) {
/* start += length */
PyObject *tmp = PyNumber_Add(start, length);
Py_DECREF(start);
@ -404,20 +387,20 @@ slice_indices(PySliceObject* self, PyObject* len)
if (start == NULL)
goto error;
cmp = PyObject_RichCompareBool(start, lower, Py_LT);
if (cmp < 0)
cmp_result = PyObject_RichCompareBool(start, lower, Py_LT);
if (cmp_result < 0)
goto error;
if (cmp) {
if (cmp_result) {
Py_INCREF(lower);
Py_DECREF(start);
start = lower;
}
}
else {
cmp = PyObject_RichCompareBool(start, upper, Py_GT);
if (cmp < 0)
cmp_result = PyObject_RichCompareBool(start, upper, Py_GT);
if (cmp_result < 0)
goto error;
if (cmp) {
if (cmp_result) {
Py_INCREF(upper);
Py_DECREF(start);
start = upper;
@ -435,10 +418,7 @@ slice_indices(PySliceObject* self, PyObject* len)
if (stop == NULL)
goto error;
cmp = PyObject_RichCompareBool(stop, zero, Py_LT);
if (cmp < 0)
goto error;
if (cmp) {
if (_PyLong_Sign(stop) < 0) {
/* stop += length */
PyObject *tmp = PyNumber_Add(stop, length);
Py_DECREF(stop);
@ -446,20 +426,20 @@ slice_indices(PySliceObject* self, PyObject* len)
if (stop == NULL)
goto error;
cmp = PyObject_RichCompareBool(stop, lower, Py_LT);
if (cmp < 0)
cmp_result = PyObject_RichCompareBool(stop, lower, Py_LT);
if (cmp_result < 0)
goto error;
if (cmp) {
if (cmp_result) {
Py_INCREF(lower);
Py_DECREF(stop);
stop = lower;
}
}
else {
cmp = PyObject_RichCompareBool(stop, upper, Py_GT);
if (cmp < 0)
cmp_result = PyObject_RichCompareBool(stop, upper, Py_GT);
if (cmp_result < 0)
goto error;
if (cmp) {
if (cmp_result) {
Py_INCREF(upper);
Py_DECREF(stop);
stop = upper;
@ -467,23 +447,51 @@ slice_indices(PySliceObject* self, PyObject* len)
}
}
*start_ptr = start;
*stop_ptr = stop;
*step_ptr = step;
Py_DECREF(upper);
Py_DECREF(lower);
Py_DECREF(length);
Py_DECREF(zero);
return Py_BuildValue("(NNN)", start, stop, step);
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);
Py_XDECREF(length);
Py_XDECREF(zero);
return NULL;
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;
}
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,
"S.indices(len) -> (start, stop, stride)\n\