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gh-143050: Add helper _PyLong_InitTag() (#147956)

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With this we can assume, that _PyLong_SetSignAndDigitCount() and
_PyLong_SetDigitCount() operate on non-immortal integers.

Co-authored-by: Victor Stinner <vstinner@python.org>
This commit is contained in:
Sergey B Kirpichev 2026-04-02 00:42:10 +03:00 • committed by GitHub
parent 4810beddbf
commit b456cb25a9
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2 changed files with 33 additions and 14 deletions
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21
Include/internal/pycore_long.h
View file

@ -238,11 +238,12 @@ _PyLong_IsSmallInt(const PyLongObject *op)
{
assert(PyLong_Check(op));
bool is_small_int = (op->long_value.lv_tag & IMMORTALITY_BIT_MASK) != 0;
assert(PyLong_CheckExact(op) || (!is_small_int));
assert(_Py_IsImmortal(op) || (!is_small_int));
assert((_PyLong_IsCompact(op)
&& _PY_IS_SMALL_INT(_PyLong_CompactValue(op)))
|| (!is_small_int));
if (is_small_int) {
assert(PyLong_CheckExact(op));
assert(_Py_IsImmortal(op));
assert((_PyLong_IsCompact(op)
&& _PY_IS_SMALL_INT(_PyLong_CompactValue(op))));
}
return is_small_int;
}
@ -285,6 +286,14 @@ _PyLong_SameSign(const PyLongObject *a, const PyLongObject *b)
return (a->long_value.lv_tag & SIGN_MASK) == (b->long_value.lv_tag & SIGN_MASK);
}
/* Initialize the tag of a freshly-allocated int. */
static inline void
_PyLong_InitTag(PyLongObject *op)
{
assert(PyLong_Check(op));
op->long_value.lv_tag = SIGN_ZERO; /* non-immortal zero */
}
#define TAG_FROM_SIGN_AND_SIZE(sign, size) \
((uintptr_t)(1 - (sign)) | ((uintptr_t)(size) << NON_SIZE_BITS))
@ -294,6 +303,7 @@ _PyLong_SetSignAndDigitCount(PyLongObject *op, int sign, Py_ssize_t size)
assert(size >= 0);
assert(-1 <= sign && sign <= 1);
assert(sign != 0 || size == 0);
assert(!_PyLong_IsSmallInt(op));
op->long_value.lv_tag = TAG_FROM_SIGN_AND_SIZE(sign, size);
}
@ -301,6 +311,7 @@ static inline void
_PyLong_SetDigitCount(PyLongObject *op, Py_ssize_t size)
{
assert(size >= 0);
assert(!_PyLong_IsSmallInt(op));
op->long_value.lv_tag = (((size_t)size) << NON_SIZE_BITS) | (op->long_value.lv_tag & SIGN_MASK);
}

26
Objects/longobject.c
View file

@ -185,6 +185,7 @@ long_alloc(Py_ssize_t size)
return NULL;
}
_PyObject_Init((PyObject*)result, &PyLong_Type);
_PyLong_InitTag(result);
}
_PyLong_SetSignAndDigitCount(result, size != 0, size);
/* The digit has to be initialized explicitly to avoid
@ -258,6 +259,7 @@ _PyLong_FromMedium(sdigit x)
return NULL;
}
_PyObject_Init((PyObject*)v, &PyLong_Type);
_PyLong_InitTag(v);
}
digit abs_x = x < 0 ? -x : x;
_PyLong_SetSignAndDigitCount(v, x<0?-1:1, 1);
@ -337,6 +339,7 @@ medium_from_stwodigits(stwodigits x)
return PyStackRef_NULL;
}
_PyObject_Init((PyObject*)v, &PyLong_Type);
_PyLong_InitTag(v);
}
digit abs_x = x < 0 ? (digit)(-x) : (digit)x;
_PyLong_SetSignAndDigitCount(v, x<0?-1:1, 1);
@ -6011,29 +6014,34 @@ static PyObject *
long_subtype_new(PyTypeObject *type, PyObject *x, PyObject *obase)
{
PyLongObject *tmp, *newobj;
Py_ssize_t i, n;
Py_ssize_t size, ndigits;
int sign;
assert(PyType_IsSubtype(type, &PyLong_Type));
tmp = (PyLongObject *)long_new_impl(&PyLong_Type, x, obase);
if (tmp == NULL)
return NULL;
assert(PyLong_Check(tmp));
n = _PyLong_DigitCount(tmp);
size = _PyLong_DigitCount(tmp);
/* Fast operations for single digit integers (including zero)
* assume that there is always at least one digit present. */
if (n == 0) {
n = 1;
}
newobj = (PyLongObject *)type->tp_alloc(type, n);
ndigits = size ? size : 1;
newobj = (PyLongObject *)type->tp_alloc(type, ndigits);
if (newobj == NULL) {
Py_DECREF(tmp);
return NULL;
}
assert(PyLong_Check(newobj));
newobj->long_value.lv_tag = tmp->long_value.lv_tag & ~IMMORTALITY_BIT_MASK;
for (i = 0; i < n; i++) {
newobj->long_value.ob_digit[i] = tmp->long_value.ob_digit[i];
if (_PyLong_IsCompact(tmp)) {
sign = _PyLong_CompactSign(tmp);
}
else {
sign = _PyLong_NonCompactSign(tmp);
}
_PyLong_InitTag(newobj);
_PyLong_SetSignAndDigitCount(newobj, sign, size);
memcpy(newobj->long_value.ob_digit, tmp->long_value.ob_digit,
ndigits * sizeof(digit));
Py_DECREF(tmp);
return (PyObject *)newobj;
}