https://github.com/python/cpython/commit/d754f75f42f040267d818ab804ada340f55e5925
commit: d754f75f42f040267d818ab804ada340f55e5925
branch: main
author: Pieter Eendebak <pieter.eende...@gmail.com>
committer: vstinner <vstin...@python.org>
date: 2025-07-10T13:16:01+02:00
summary:
gh-82088: Improve performance of PyLong_As*() for multi-digit ints (#135585)
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstin...@python.org>
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2025-06-17-08-37-45.gh-issue-82088.TgPvLg.rst
M Objects/longobject.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2025-06-17-08-37-45.gh-issue-82088.TgPvLg.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2025-06-17-08-37-45.gh-issue-82088.TgPvLg.rst
new file mode 100644
index 00000000000000..74bd182c1990f8
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2025-06-17-08-37-45.gh-issue-82088.TgPvLg.rst
@@ -0,0 +1,5 @@
+Improve performance of ``PyLongObject`` conversion functions
+``PyLong_AsLongAndOverflow()``, ``PyLong_AsSsize_t()``,
``PyLong_AsUnsignedLong()``, ``PyLong_AsSize_t()``,
+``PyLong_AsUnsignedLongMask()``, ``PyLong_AsUnsignedLongLongMask()``,
``PyLong_AsLongLongAndOverflow()``
+for integers larger than 2**30 up to 30%.
+
diff --git a/Objects/longobject.c b/Objects/longobject.c
index 557bb6e1dd956c..581db10b54ab57 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -526,6 +526,54 @@ PyLong_FromDouble(double dval)
#define PY_ABS_LONG_MIN (0-(unsigned long)LONG_MIN)
#define PY_ABS_SSIZE_T_MIN (0-(size_t)PY_SSIZE_T_MIN)
+static inline unsigned long
+unroll_digits_ulong(PyLongObject *v, Py_ssize_t *iptr)
+{
+ assert(ULONG_MAX >= ((1UL << PyLong_SHIFT) - 1));
+
+ Py_ssize_t i = *iptr;
+ assert(i >= 2);
+
+ /* unroll 1 digit */
+ --i;
+ digit *digits = v->long_value.ob_digit;
+ unsigned long x = digits[i];
+
+#if (ULONG_MAX >> PyLong_SHIFT) >= ((1UL << PyLong_SHIFT) - 1)
+ /* unroll another digit */
+ x <<= PyLong_SHIFT;
+ --i;
+ x |= digits[i];
+#endif
+
+ *iptr = i;
+ return x;
+}
+
+static inline size_t
+unroll_digits_size_t(PyLongObject *v, Py_ssize_t *iptr)
+{
+ assert(SIZE_MAX >= ((1UL << PyLong_SHIFT) - 1));
+
+ Py_ssize_t i = *iptr;
+ assert(i >= 2);
+
+ /* unroll 1 digit */
+ --i;
+ digit *digits = v->long_value.ob_digit;
+ size_t x = digits[i];
+
+#if (SIZE_MAX >> PyLong_SHIFT) >= ((1 << PyLong_SHIFT) - 1)
+ /* unroll another digit */
+ x <<= PyLong_SHIFT;
+ --i;
+ x |= digits[i];
+#endif
+
+ *iptr = i;
+ return x;
+}
+
/* Get a C long int from an int object or any object that has an __index__
method.
@@ -535,13 +583,11 @@ PyLong_FromDouble(double dval)
For other errors (e.g., TypeError), return -1 and set an error condition.
In this case *overflow will be 0.
*/
-
long
PyLong_AsLongAndOverflow(PyObject *vv, int *overflow)
{
- /* This version by Tim Peters */
+ /* This version originally by Tim Peters */
PyLongObject *v;
- unsigned long x, prev;
long res;
Py_ssize_t i;
int sign;
@@ -584,14 +630,14 @@ PyLong_AsLongAndOverflow(PyObject *vv, int *overflow)
res = -1;
i = _PyLong_DigitCount(v);
sign = _PyLong_NonCompactSign(v);
- x = 0;
+
+ unsigned long x = unroll_digits_ulong(v, &i);
while (--i >= 0) {
- prev = x;
- x = (x << PyLong_SHIFT) | v->long_value.ob_digit[i];
- if ((x >> PyLong_SHIFT) != prev) {
+ if (x > (ULONG_MAX >> PyLong_SHIFT)) {
*overflow = sign;
goto exit;
}
+ x = (x << PyLong_SHIFT) | v->long_value.ob_digit[i];
}
/* Haven't lost any bits, but casting to long requires extra
* care (see comment above).
@@ -655,7 +701,6 @@ PyLong_AsInt(PyObject *obj)
Py_ssize_t
PyLong_AsSsize_t(PyObject *vv) {
PyLongObject *v;
- size_t x, prev;
Py_ssize_t i;
int sign;
@@ -674,12 +719,13 @@ PyLong_AsSsize_t(PyObject *vv) {
}
i = _PyLong_DigitCount(v);
sign = _PyLong_NonCompactSign(v);
- x = 0;
+
+ size_t x = unroll_digits_size_t(v, &i);
while (--i >= 0) {
- prev = x;
- x = (x << PyLong_SHIFT) | v->long_value.ob_digit[i];
- if ((x >> PyLong_SHIFT) != prev)
+ if (x > (SIZE_MAX >> PyLong_SHIFT)) {
goto overflow;
+ }
+ x = (x << PyLong_SHIFT) | v->long_value.ob_digit[i];
}
/* Haven't lost any bits, but casting to a signed type requires
* extra care (see comment above).
@@ -705,7 +751,6 @@ unsigned long
PyLong_AsUnsignedLong(PyObject *vv)
{
PyLongObject *v;
- unsigned long x, prev;
Py_ssize_t i;
if (vv == NULL) {
@@ -736,13 +781,13 @@ PyLong_AsUnsignedLong(PyObject *vv)
return (unsigned long) -1;
}
i = _PyLong_DigitCount(v);
- x = 0;
+
+ unsigned long x = unroll_digits_ulong(v, &i);
while (--i >= 0) {
- prev = x;
- x = (x << PyLong_SHIFT) | v->long_value.ob_digit[i];
- if ((x >> PyLong_SHIFT) != prev) {
+ if (x > (ULONG_MAX >> PyLong_SHIFT)) {
goto overflow;
}
+ x = (x << PyLong_SHIFT) | v->long_value.ob_digit[i];
}
return x;
overflow:
@@ -759,7 +804,6 @@ size_t
PyLong_AsSize_t(PyObject *vv)
{
PyLongObject *v;
- size_t x, prev;
Py_ssize_t i;
if (vv == NULL) {
@@ -781,16 +825,16 @@ PyLong_AsSize_t(PyObject *vv)
return (size_t) -1;
}
i = _PyLong_DigitCount(v);
- x = 0;
+
+ size_t x = unroll_digits_size_t(v, &i);
while (--i >= 0) {
- prev = x;
- x = (x << PyLong_SHIFT) | v->long_value.ob_digit[i];
- if ((x >> PyLong_SHIFT) != prev) {
- PyErr_SetString(PyExc_OverflowError,
- "Python int too large to convert to C size_t");
- return (size_t) -1;
+ if (x > (SIZE_MAX >> PyLong_SHIFT)) {
+ PyErr_SetString(PyExc_OverflowError,
+ "Python int too large to convert to C size_t");
+ return (size_t) -1;
+ }
+ x = (x << PyLong_SHIFT) | v->long_value.ob_digit[i];
}
- }
return x;
}
@@ -801,7 +845,6 @@ static unsigned long
_PyLong_AsUnsignedLongMask(PyObject *vv)
{
PyLongObject *v;
- unsigned long x;
Py_ssize_t i;
if (vv == NULL || !PyLong_Check(vv)) {
@@ -818,7 +861,7 @@ _PyLong_AsUnsignedLongMask(PyObject *vv)
}
i = _PyLong_DigitCount(v);
int sign = _PyLong_NonCompactSign(v);
- x = 0;
+ unsigned long x = unroll_digits_ulong(v, &i);
while (--i >= 0) {
x = (x << PyLong_SHIFT) | v->long_value.ob_digit[i];
}
@@ -1619,7 +1662,6 @@ static unsigned long long
_PyLong_AsUnsignedLongLongMask(PyObject *vv)
{
PyLongObject *v;
- unsigned long long x;
Py_ssize_t i;
int sign;
@@ -1637,7 +1679,7 @@ _PyLong_AsUnsignedLongLongMask(PyObject *vv)
}
i = _PyLong_DigitCount(v);
sign = _PyLong_NonCompactSign(v);
- x = 0;
+ unsigned long long x = unroll_digits_ulong(v, &i);
while (--i >= 0) {
x = (x << PyLong_SHIFT) | v->long_value.ob_digit[i];
}
@@ -1683,7 +1725,6 @@ PyLong_AsLongLongAndOverflow(PyObject *vv, int *overflow)
{
/* This version by Tim Peters */
PyLongObject *v;
- unsigned long long x, prev;
long long res;
Py_ssize_t i;
int sign;
@@ -1725,15 +1766,14 @@ PyLong_AsLongLongAndOverflow(PyObject *vv, int
*overflow)
else {
i = _PyLong_DigitCount(v);
sign = _PyLong_NonCompactSign(v);
- x = 0;
+ unsigned long long x = unroll_digits_ulong(v, &i);
while (--i >= 0) {
- prev = x;
- x = (x << PyLong_SHIFT) + v->long_value.ob_digit[i];
- if ((x >> PyLong_SHIFT) != prev) {
+ if (x > ULLONG_MAX >> PyLong_SHIFT) {
*overflow = sign;
res = -1;
goto exit;
}
+ x = (x << PyLong_SHIFT) + v->long_value.ob_digit[i];
}
/* Haven't lost any bits, but casting to long requires extra
* care (see comment above).
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