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gh-129149: Add fast path for medium-sized integers in PyLong_FromSsize_t() (#129301)

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The implementation of `PyLong_FromLong()`, `PyLong_FromLongLong()` and `PyLong_FromSsize_t()`
are now handled by a common macro `PYLONG_FROM_INT` which contains fast paths depending on the
size of the integer to convert. Consequently, `PyLong_FromSsize_t()` for medium-sized integers is faster
by roughly 25%.

---------

Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>
This commit is contained in:
Chris Eibl 2025-03-13 12:06:56 +01:00 committed by GitHub
parent a005835f69
commit 119bcfad9c
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GPG Key ID: B5690EEEBB952194
3 changed files with 44 additions and 107 deletions
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4
Lib/test/test_capi/test_long.py
View File

@ -168,9 +168,9 @@ class LongTests(unittest.TestCase):
mask=False,
negative_value_error=OverflowError):
# round trip (object -> C integer -> object)
values = (0, 1, 1234, max_val)
values = (0, 1, 512, 1234, max_val)
if min_val < 0:
values += (-1, min_val)
values += (-1, -512, -1234, min_val)
for value in values:
with self.subTest(value=value):
self.assertEqual(func(value), value)

2
Misc/NEWS.d/next/Core_and_Builtins/2025-01-25-20-07-03.gh-issue-129149.njeFJi.rst Normal file
View File

@ -0,0 +1,2 @@
Add fast path for medium-size integers in :c:func:`PyLong_FromSsize_t`.
Patch by Chris Eibl.

145
Objects/longobject.c
View File

@ -332,49 +332,51 @@ _PyLong_Negate(PyLongObject **x_p)
Py_DECREF(x);
}
#define PYLONG_FROM_INT(UINT_TYPE, INT_TYPE, ival) \
do { \
/* Handle small and medium cases. */ \
if (IS_SMALL_INT(ival)) { \
return get_small_int((sdigit)(ival)); \
} \
if (-(INT_TYPE)PyLong_MASK <= (ival) && (ival) <= (INT_TYPE)PyLong_MASK) { \
return _PyLong_FromMedium((sdigit)(ival)); \
} \
UINT_TYPE abs_ival = (ival) < 0 ? 0U-(UINT_TYPE)(ival) : (UINT_TYPE)(ival); \
/* Do shift in two steps to avoid possible undefined behavior. */ \
UINT_TYPE t = abs_ival >> PyLong_SHIFT >> PyLong_SHIFT; \
/* Count digits (at least two - smaller cases were handled above). */ \
Py_ssize_t ndigits = 2; \
while (t) { \
++ndigits; \
t >>= PyLong_SHIFT; \
} \
/* Construct output value. */ \
PyLongObject *v = long_alloc(ndigits); \
if (v == NULL) { \
return NULL; \
} \
digit *p = v->long_value.ob_digit; \
_PyLong_SetSignAndDigitCount(v, (ival) < 0 ? -1 : 1, ndigits); \
t = abs_ival; \
while (t) { \
*p++ = (digit)(t & PyLong_MASK); \
t >>= PyLong_SHIFT; \
} \
return (PyObject *)v; \
} while(0)
/* Create a new int object from a C long int */
PyObject *
PyLong_FromLong(long ival)
{
PyLongObject *v;
unsigned long abs_ival, t;
int ndigits;
/* Handle small and medium cases. */
if (IS_SMALL_INT(ival)) {
return get_small_int((sdigit)ival);
}
if (-(long)PyLong_MASK <= ival && ival <= (long)PyLong_MASK) {
return _PyLong_FromMedium((sdigit)ival);
}
/* Count digits (at least two - smaller cases were handled above). */
abs_ival = ival < 0 ? 0U-(unsigned long)ival : (unsigned long)ival;
/* Do shift in two steps to avoid possible undefined behavior. */
t = abs_ival >> PyLong_SHIFT >> PyLong_SHIFT;
ndigits = 2;
while (t) {
++ndigits;
t >>= PyLong_SHIFT;
}
/* Construct output value. */
v = long_alloc(ndigits);
if (v != NULL) {
digit *p = v->long_value.ob_digit;
_PyLong_SetSignAndDigitCount(v, ival < 0 ? -1 : 1, ndigits);
t = abs_ival;
while (t) {
*p++ = (digit)(t & PyLong_MASK);
t >>= PyLong_SHIFT;
}
}
return (PyObject *)v;
PYLONG_FROM_INT(unsigned long, long, ival);
}
#define PYLONG_FROM_UINT(INT_TYPE, ival) \
do { \
/* Handle small and medium cases. */ \
if (IS_SMALL_UINT(ival)) { \
return get_small_int((sdigit)(ival)); \
} \
@ -383,12 +385,13 @@ PyLong_FromLong(long ival)
} \
/* Do shift in two steps to avoid possible undefined behavior. */ \
INT_TYPE t = (ival) >> PyLong_SHIFT >> PyLong_SHIFT; \
/* Count the number of Python digits. */ \
/* Count digits (at least two - smaller cases were handled above). */ \
Py_ssize_t ndigits = 2; \
while (t) { \
++ndigits; \
t >>= PyLong_SHIFT; \
} \
/* Construct output value. */ \
PyLongObject *v = long_alloc(ndigits); \
if (v == NULL) { \
return NULL; \
@ -1482,40 +1485,7 @@ PyLong_AsVoidPtr(PyObject *vv)
PyObject *
PyLong_FromLongLong(long long ival)
{
PyLongObject *v;
unsigned long long abs_ival, t;
int ndigits;
/* Handle small and medium cases. */
if (IS_SMALL_INT(ival)) {
return get_small_int((sdigit)ival);
}
if (-(long long)PyLong_MASK <= ival && ival <= (long long)PyLong_MASK) {
return _PyLong_FromMedium((sdigit)ival);
}
/* Count digits (at least two - smaller cases were handled above). */
abs_ival = ival < 0 ? 0U-(unsigned long long)ival : (unsigned long long)ival;
/* Do shift in two steps to avoid possible undefined behavior. */
t = abs_ival >> PyLong_SHIFT >> PyLong_SHIFT;
ndigits = 2;
while (t) {
++ndigits;
t >>= PyLong_SHIFT;
}
/* Construct output value. */
v = long_alloc(ndigits);
if (v != NULL) {
digit *p = v->long_value.ob_digit;
_PyLong_SetSignAndDigitCount(v, ival < 0 ? -1 : 1, ndigits);
t = abs_ival;
while (t) {
*p++ = (digit)(t & PyLong_MASK);
t >>= PyLong_SHIFT;
}
}
return (PyObject *)v;
PYLONG_FROM_INT(unsigned long long, long long, ival);
}
/* Create a new int object from a C Py_ssize_t. */
@ -1523,42 +1493,7 @@ PyLong_FromLongLong(long long ival)
PyObject *
PyLong_FromSsize_t(Py_ssize_t ival)
{
PyLongObject *v;
size_t abs_ival;
size_t t; /* unsigned so >> doesn't propagate sign bit */
int ndigits = 0;
int negative = 0;
if (IS_SMALL_INT(ival)) {
return get_small_int((sdigit)ival);
}
if (ival < 0) {
/* avoid signed overflow when ival = SIZE_T_MIN */
abs_ival = (size_t)(-1-ival)+1;
negative = 1;
}
else {
abs_ival = (size_t)ival;
}
/* Count the number of Python digits. */
t = abs_ival;
while (t) {
++ndigits;
t >>= PyLong_SHIFT;
}
v = long_alloc(ndigits);
if (v != NULL) {
digit *p = v->long_value.ob_digit;
_PyLong_SetSignAndDigitCount(v, negative ? -1 : 1, ndigits);
t = abs_ival;
while (t) {
*p++ = (digit)(t & PyLong_MASK);
t >>= PyLong_SHIFT;
}
}
return (PyObject *)v;
PYLONG_FROM_INT(size_t, Py_ssize_t, ival);
}
/* Get a C long long int from an int object or any object that has an