bpo-37128: Add math.perm(). (GH-13731)
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index bea4607..6e10993 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -2999,6 +2999,120 @@
/*[clinic input]
+math.perm
+
+ n: object
+ k: object
+ /
+
+Number of ways to choose k items from n items without repetition and with order.
+
+It is mathematically equal to the expression n! / (n - k)!.
+
+Raises TypeError if the arguments are not integers.
+Raises ValueError if the arguments are negative or if k > n.
+[clinic start generated code]*/
+
+static PyObject *
+math_perm_impl(PyObject *module, PyObject *n, PyObject *k)
+/*[clinic end generated code: output=e021a25469653e23 input=f71ee4f6ff26be24]*/
+{
+ PyObject *result = NULL, *factor = NULL;
+ int overflow, cmp;
+ long long i, factors;
+
+ n = PyNumber_Index(n);
+ if (n == NULL) {
+ return NULL;
+ }
+ if (!PyLong_CheckExact(n)) {
+ Py_SETREF(n, _PyLong_Copy((PyLongObject *)n));
+ if (n == NULL) {
+ return NULL;
+ }
+ }
+ k = PyNumber_Index(k);
+ if (k == NULL) {
+ Py_DECREF(n);
+ return NULL;
+ }
+ if (!PyLong_CheckExact(k)) {
+ Py_SETREF(k, _PyLong_Copy((PyLongObject *)k));
+ if (k == NULL) {
+ Py_DECREF(n);
+ return NULL;
+ }
+ }
+
+ if (Py_SIZE(n) < 0) {
+ PyErr_SetString(PyExc_ValueError,
+ "n must be a non-negative integer");
+ goto error;
+ }
+ cmp = PyObject_RichCompareBool(n, k, Py_LT);
+ if (cmp != 0) {
+ if (cmp > 0) {
+ PyErr_SetString(PyExc_ValueError,
+ "k must be an integer less than or equal to n");
+ }
+ goto error;
+ }
+
+ factors = PyLong_AsLongLongAndOverflow(k, &overflow);
+ if (overflow > 0) {
+ PyErr_Format(PyExc_OverflowError,
+ "k must not exceed %lld",
+ LLONG_MAX);
+ goto error;
+ }
+ else if (overflow < 0 || factors < 0) {
+ if (!PyErr_Occurred()) {
+ PyErr_SetString(PyExc_ValueError,
+ "k must be a non-negative integer");
+ }
+ goto error;
+ }
+
+ if (factors == 0) {
+ result = PyLong_FromLong(1);
+ goto done;
+ }
+
+ result = n;
+ Py_INCREF(result);
+ if (factors == 1) {
+ goto done;
+ }
+
+ factor = n;
+ Py_INCREF(factor);
+ for (i = 1; i < factors; ++i) {
+ Py_SETREF(factor, PyNumber_Subtract(factor, _PyLong_One));
+ if (factor == NULL) {
+ goto error;
+ }
+ Py_SETREF(result, PyNumber_Multiply(result, factor));
+ if (result == NULL) {
+ goto error;
+ }
+ }
+ Py_DECREF(factor);
+
+done:
+ Py_DECREF(n);
+ Py_DECREF(k);
+ return result;
+
+error:
+ Py_XDECREF(factor);
+ Py_XDECREF(result);
+ Py_DECREF(n);
+ Py_DECREF(k);
+ return NULL;
+}
+
+
+/*[clinic input]
math.comb
n: object
@@ -3028,11 +3142,24 @@
if (n == NULL) {
return NULL;
}
+ if (!PyLong_CheckExact(n)) {
+ Py_SETREF(n, _PyLong_Copy((PyLongObject *)n));
+ if (n == NULL) {
+ return NULL;
+ }
+ }
k = PyNumber_Index(k);
if (k == NULL) {
Py_DECREF(n);
return NULL;
}
+ if (!PyLong_CheckExact(k)) {
+ Py_SETREF(k, _PyLong_Copy((PyLongObject *)k));
+ if (k == NULL) {
+ Py_DECREF(n);
+ return NULL;
+ }
+ }
if (Py_SIZE(n) < 0) {
PyErr_SetString(PyExc_ValueError,
@@ -3050,7 +3177,7 @@
"k must be an integer less than or equal to n");
goto error;
}
- cmp = PyObject_RichCompareBool(k, temp, Py_GT);
+ cmp = PyObject_RichCompareBool(temp, k, Py_LT);
if (cmp > 0) {
Py_SETREF(k, temp);
}
@@ -3174,6 +3301,7 @@
{"tanh", math_tanh, METH_O, math_tanh_doc},
MATH_TRUNC_METHODDEF
MATH_PROD_METHODDEF
+ MATH_PERM_METHODDEF
MATH_COMB_METHODDEF
{NULL, NULL} /* sentinel */
};