From 7edc52a3908b01e1ae767a561dc4b3641addda91 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Thu, 27 May 2021 00:51:07 +0200
Subject: [PATCH] bpo-42161: mathmodule.c: move _PyLong_GetOne() loop invariant
 (GH-26391)

Move _PyLong_GetZero() and _PyLong_GetOne() loop invariants outside
loops in functions:

* math.comb()
* math.gcd()
* math.lcm()
* math.perm()
(cherry picked from commit 3e7ee02327db13e4337374597cdc4458ecb9e3ad)

Co-authored-by: Victor Stinner <vstinner@python.org>
---
 Modules/mathmodule.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index d0dd12d25966a1..a2a2db29be343d 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -845,13 +845,15 @@ math_gcd(PyObject *module, PyObject * const *args, Py_ssize_t nargs)
         Py_SETREF(res, PyNumber_Absolute(res));
         return res;
     }
+
+    PyObject *one = _PyLong_GetOne();  // borrowed ref
     for (i = 1; i < nargs; i++) {
         x = _PyNumber_Index(args[i]);
         if (x == NULL) {
             Py_DECREF(res);
             return NULL;
         }
-        if (res == _PyLong_GetOne()) {
+        if (res == one) {
             /* Fast path: just check arguments.
                It is okay to use identity comparison here. */
             Py_DECREF(x);
@@ -918,13 +920,15 @@ math_lcm(PyObject *module, PyObject * const *args, Py_ssize_t nargs)
         Py_SETREF(res, PyNumber_Absolute(res));
         return res;
     }
+
+    PyObject *zero = _PyLong_GetZero();  // borrowed ref
     for (i = 1; i < nargs; i++) {
         x = PyNumber_Index(args[i]);
         if (x == NULL) {
             Py_DECREF(res);
             return NULL;
         }
-        if (res == _PyLong_GetZero()) {
+        if (res == zero) {
             /* Fast path: just check arguments.
                It is okay to use identity comparison here. */
             Py_DECREF(x);
@@ -3293,10 +3297,10 @@ math_perm_impl(PyObject *module, PyObject *n, PyObject *k)
         goto done;
     }
 
-    factor = n;
-    Py_INCREF(factor);
+    factor = Py_NewRef(n);
+    PyObject *one = _PyLong_GetOne();  // borrowed ref
     for (i = 1; i < factors; ++i) {
-        Py_SETREF(factor, PyNumber_Subtract(factor, _PyLong_GetOne()));
+        Py_SETREF(factor, PyNumber_Subtract(factor, one));
         if (factor == NULL) {
             goto error;
         }
@@ -3415,10 +3419,10 @@ math_comb_impl(PyObject *module, PyObject *n, PyObject *k)
         goto done;
     }
 
-    factor = n;
-    Py_INCREF(factor);
+    factor = Py_NewRef(n);
+    PyObject *one = _PyLong_GetOne();  // borrowed ref
     for (i = 1; i < factors; ++i) {
-        Py_SETREF(factor, PyNumber_Subtract(factor, _PyLong_GetOne()));
+        Py_SETREF(factor, PyNumber_Subtract(factor, one));
         if (factor == NULL) {
             goto error;
         }