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gh-132108: Add Buffer Protocol support to int.from_bytes to improve performance #132109

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gh-132108: Add Buffer Protocol support to int.from_bytes to improve performance #132109

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gh-132108: Add Buffer Protocol support to int.from_bytes
cmaloney Apr 5, 2025
b078ea1
Apply suggestions from code review
cmaloney Apr 7, 2025
e6ef5e1
Check bytes exact first to speed up that case
cmaloney Apr 9, 2025
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-04-04-20-38-29.gh-issue-132108.UwZIQy.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Speed up :meth:`int.from_bytes` when passed object supports :ref:`buffer
protocol <bufferobjects>`, like :class:`bytearray` by ~1.2x.
33 changes: 25 additions & 8 deletions Objects/longobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6439,6 +6439,7 @@ int_from_bytes_impl(PyTypeObject *type, PyObject *bytes_obj,
{
int little_endian;
PyObject *long_obj, *bytes;
Py_buffer view;

if (byteorder == NULL)
little_endian = 0;
Expand All @@ -6452,14 +6453,30 @@ int_from_bytes_impl(PyTypeObject *type, PyObject *bytes_obj,
return NULL;
}

bytes = PyObject_Bytes(bytes_obj);
if (bytes == NULL)
return NULL;

long_obj = _PyLong_FromByteArray(
(unsigned char *)PyBytes_AS_STRING(bytes), Py_SIZE(bytes),
little_endian, is_signed);
Py_DECREF(bytes);
/* Use buffer protocol to avoid copies. */
if (PyBytes_CheckExact(bytes_obj)) {
long_obj = _PyLong_FromByteArray(
(unsigned char *)PyBytes_AS_STRING(bytes_obj), Py_SIZE(bytes_obj),
little_endian, is_signed);
} else if (PyObject_CheckBuffer(bytes_obj)) {
if (PyObject_GetBuffer(bytes_obj, &view, PyBUF_SIMPLE) != 0) {
return NULL;
}
long_obj = _PyLong_FromByteArray(view.buf, view.len, little_endian,
is_signed);
PyBuffer_Release(&view);
}
else {
/* fallback: Construct a bytes then convert. */
bytes = PyObject_Bytes(bytes_obj);
if (bytes == NULL) {
return NULL;
}
long_obj = _PyLong_FromByteArray(
(unsigned char *)PyBytes_AS_STRING(bytes), Py_SIZE(bytes),
little_endian, is_signed);
Py_DECREF(bytes);
}

if (long_obj != NULL && type != &PyLong_Type) {
Py_SETREF(long_obj, PyObject_CallOneArg((PyObject *)type, long_obj));
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