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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
+34 −18
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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address review: some comments
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@skirpichev
skirpichev committed Mar 28, 2026
commit 1f363f41256562347be497789450d74af071a67a
1 change: 1 addition & 0 deletions Include/internal/pycore_long.h
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Expand Up @@ -231,6 +231,7 @@ _PyLong_IsPositive(const PyLongObject *op)
return (op->long_value.lv_tag & SIGN_MASK) == 0;
}

/* Return true if the argument is a small int */
static inline bool
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_PyLong_HasImmortalTag(const PyLongObject *op)
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@vstinner vstinner Mar 30, 2026

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IMO the intent here is to check if an integer is a small integer, rather than checking for a tag. So I would prefer to rename the function to _PyLong_IsSmallInt().

I wanted to suggest referring to _PY_IS_SMALL_INT() but I noticed the macro is wrong. I wrote #146631 to fix the macro.

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@skirpichev skirpichev Mar 30, 2026

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There are two notions for "small int"'s. One - by value and other is - this. If @colesbury is ok - I'm fine with renaming..

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@vstinner vstinner Mar 30, 2026

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_PyLong_HasImmortalTag() and _PY_IS_SMALL_INT() should be true or false for the same values.

For example, you can add the following check for _PyLong_HasImmortalTag():

+    assert((_PyLong_IsCompact(op) && _PY_IS_SMALL_INT(_PyLong_CompactValue(op)))
+           || (!is_small_int));

(You need to update your branch to retrieve my _PY_IS_SMALL_INT() change.)

For me, testing IMMORTALITY_BIT_MASK is just an implementation detail to check if an integer is "a small int".

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@skirpichev skirpichev Mar 31, 2026

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I've added an assert. BTW, what do you think on #145901 (comment)?

I don't think we should mention _PY_IS_SMALL_INT in the description of the function, assert is readable enough.

For me, testing IMMORTALITY_BIT_MASK is just an implementation detail to check if an integer is "a small int".

For now, we use _PY_IS_SMALL_INT() to check this. But eventually this could be just testing a flag.

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@vstinner vstinner Mar 31, 2026

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I would prefer to rename the function to _PyLong_IsSmallInt().

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@skirpichev skirpichev Mar 31, 2026

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I've added suggestions.

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3 changes: 3 additions & 0 deletions Lib/test/test_capi/test_long.py
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Expand Up @@ -805,8 +805,11 @@ def to_digits(num):

def test_bug_143050(self):
with support.adjust_int_max_str_digits(0):
# Bug coming from using _pylong.int_from_string(), that
# currently requires > 6000 decimal digits.
int('-' + '0' * 7000, 10)
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_testcapi.test_immortal_small_ints()
# Test also nonzero small int
int('-' + '0' * 7000 + '123', 10)
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_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


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