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gh-143050: correct PyLong_FromString() to use _PyLong_Negate() #145901

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Merged
vstinner merged 13 commits into from
Mar 31, 2026
Merged

gh-143050: correct PyLong_FromString() to use _PyLong_Negate() #145901

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fbcec5a
gh-143050: correct PyLong_FromString() to use _PyLong_Negate()
skirpichev Mar 13, 2026
b8333ba
cleanup, use _testcapi.test_immortal_small_ints()
skirpichev Mar 13, 2026
20e79c6
+ add also test with nonzero small int
skirpichev Mar 14, 2026
413e56d
_long_is_small_int() -> _PyLong_IsImmortal() helper
skirpichev Mar 14, 2026
b892216
Merge branch 'master' into fix-PyLong_FromString/143050
skirpichev Mar 17, 2026
78c5b4b
address review: rename _PyLong_IsImmortal -> _PyLong_HasImmortalTag
skirpichev Mar 17, 2026
69d35bd
add assert
skirpichev Mar 18, 2026
2f927e0
address review: simplify assert
skirpichev Mar 18, 2026
53523de
Merge branch 'master' into fix-PyLong_FromString/143050
skirpichev Mar 27, 2026
1f363f4
address review: some comments
skirpichev Mar 28, 2026
41961ed
Merge branch 'main' into fix-PyLong_FromString/143050
skirpichev Mar 30, 2026
0b29e28
address review: add assert on _PY_IS_SMALL_INT
skirpichev Mar 30, 2026
45b3b04
Rename to _PyLong_IsSmallInt()
vstinner Mar 31, 2026
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6 changes: 6 additions & 0 deletions Lib/test/test_capi/test_long.py
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Original file line number Diff line number Diff line change
Expand Up @@ -803,6 +803,12 @@ def to_digits(num):
self.assertEqual(pylongwriter_create(negative, digits), num,
(negative, digits))

def test_bug_143050(self):
with support.adjust_int_max_str_digits(0):
a = int('-' + '0' * 7000, 10)
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del a
_testcapi.test_immortal_small_ints()
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@skirpichev skirpichev Mar 13, 2026

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I'm slightly worry that this pass will non-debug builds.

@corona10 (author of #103962), are you sure there is no other way to implement this helper? Return a different value, raise an error?

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@colesbury colesbury Mar 17, 2026

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That's okay as long as it catches the regression in a debug build.

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@vstinner vstinner Mar 31, 2026

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_testcapi is always built with assertions, even in release mode.

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@vstinner vstinner Mar 31, 2026

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I built Python in release mode without PyLong_FromString() fix. _PyLong_FlipSign() assertion didn't catch the bug since Python was built without assertions. But at least, test_immortal_small_ints() was able to detect that small integers were corrupted:

test_bug_143050 (test.test_capi.test_long.LongTests.test_bug_143050) ...
python: ./Modules/_testcapi/immortal.c:35: test_immortal_small_ints: Assertion `has_int_immortal_bit' failed.
Fatal Python error: Aborted

Current thread 0x00007f617b91b780 [python] (most recent call first):
  File "/home/vstinner/python/main/Lib/test/test_capi/test_long.py", line 811 in test_bug_143050



if __name__ == "__main__":
unittest.main()
6 changes: 3 additions & 3 deletions Objects/longobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3118,11 +3118,11 @@ PyLong_FromString(const char *str, char **pend, int base)
}

/* Set sign and normalize */
if (sign < 0) {
_PyLong_FlipSign(z);
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}
long_normalize(z);
z = maybe_small_long(z);
if (sign < 0) {
_PyLong_Negate(&z);
}

if (pend != NULL) {
*pend = (char *)str;
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