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gh-91117: Ensure integer mod and pow operations use cached small ints (GH-31843)

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Dennis Sweeney 2022-04-11 16:07:09 -04:00 committed by GitHub
parent a8abb76af9
commit 8be8949116
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3 changed files with 45 additions and 0 deletions
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42
Lib/test/test_long.py
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@ -1024,6 +1024,48 @@ class LongTest(unittest.TestCase):
self.assertIs(a + b, 1)
self.assertIs(c - a, 1)
@support.cpython_only
def test_pow_uses_cached_small_ints(self):
self.assertIs(pow(10, 3, 998), 2)
self.assertIs(10 ** 3 % 998, 2)
a, p, m = 10, 3, 998
self.assertIs(a ** p % m, 2)
self.assertIs(pow(2, 31, 2 ** 31 - 1), 1)
self.assertIs(2 ** 31 % (2 ** 31 - 1), 1)
a, p, m = 2, 31, 2 ** 31 - 1
self.assertIs(a ** p % m, 1)
self.assertIs(pow(2, 100, 2**100 - 3), 3)
self.assertIs(2 ** 100 % (2 ** 100 - 3), 3)
a, p, m = 2, 100, 2**100 - 3
self.assertIs(a ** p % m, 3)
@support.cpython_only
def test_divmod_uses_cached_small_ints(self):
big = 10 ** 100
self.assertIs((big + 1) % big, 1)
self.assertIs((big + 1) // big, 1)
self.assertIs(big // (big // 2), 2)
self.assertIs(big // (big // -4), -4)
q, r = divmod(2 * big + 3, big)
self.assertIs(q, 2)
self.assertIs(r, 3)
q, r = divmod(-4 * big + 100, big)
self.assertIs(q, -4)
self.assertIs(r, 100)
q, r = divmod(3 * (-big) - 1, -big)
self.assertIs(q, 3)
self.assertIs(r, -1)
q, r = divmod(3 * big - 1, -big)
self.assertIs(q, -3)
self.assertIs(r, -1)
def test_small_ints(self):
for i in range(-5, 257):
self.assertIs(i, i + 0)

1
Misc/NEWS.d/next/Core and Builtins/2022-03-13-08-23-17.bpo-46961.SgGCkG.rst Normal file
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@ -0,0 +1 @@
Integer mod/remainder operations, including the three-argument form of :func:`pow`, now consistently return ints from the global small integer cache when applicable.

2
Objects/longobject.c
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@ -2679,6 +2679,7 @@ long_divrem(PyLongObject *a, PyLongObject *b,
}
else {
z = x_divrem(a, b, prem);
*prem = maybe_small_long(*prem);
if (z == NULL)
return -1;
}
@ -2732,6 +2733,7 @@ long_rem(PyLongObject *a, PyLongObject *b, PyLongObject **prem)
else {
/* Slow path using divrem. */
Py_XDECREF(x_divrem(a, b, prem));
*prem = maybe_small_long(*prem);
if (*prem == NULL)
return -1;
}