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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
Speed up conversion from `bytes-like` objects like `bytearray` whilekeeping conversion from `bytes` stable.On a `--with-lto --enable-optimizaitons` build on my 64 bit Linux box:new:from_bytes_flags: Mean +- std dev: 28.6 ns +- 0.5 nsbench_convert[bytes]: Mean +- std dev: 50.4 ns +- 1.4 nsbench_convert[bytearray]: Mean +- std dev: 51.3 ns +- 0.7 nsold:from_bytes_flags: Mean +- std dev: 28.1 ns +- 1.1 nsbench_convert[bytes]: Mean +- std dev: 50.3 ns +- 4.3 nsbench_convert[bytearray]: Mean +- std dev: 64.7 ns +- 0.9 nsBenchmark code:```pythonimport pyperfimport timedef from_bytes_flags(loops):    range_it = range(loops)    t0 = time.perf_counter()    for _ in range_it:        int.from_bytes(b'\x00\x10', byteorder='big')        int.from_bytes(b'\x00\x10', byteorder='little')        int.from_bytes(b'\xfc\x00', byteorder='big', signed=True)        int.from_bytes(b'\xfc\x00', byteorder='big', signed=False)        int.from_bytes([255, 0, 0], byteorder='big')    return time.perf_counter() - t0sample_bytes = [    b'',    b'\x00',    b'\x01',    b'\x7f',    b'\x80',    b'\xff',    b'\x01\x00',    b'\x7f\xff',    b'\x80\x00',    b'\xff\xff',    b'\x01\x00\x00',]sample_bytearray = [bytearray(v) for v in sample_bytes]def bench_convert(loops, values):    range_it = range(loops)    t0 = time.perf_counter()    for _ in range_it:        for val in values:            int.from_bytes(val)    return time.perf_counter() - t0runner = pyperf.Runner()runner.bench_time_func('from_bytes_flags', from_bytes_flags, inner_loops=10)runner.bench_time_func('bench_convert[bytes]', bench_convert, sample_bytes, inner_loops=10)runner.bench_time_func('bench_convert[bytearray]', bench_convert, sample_bytearray, inner_loops=10)```
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@cmaloney
cmaloney committedApr 5, 2025
commitd898d27dad53846a7943a818e4010a49a53c3895
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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
Speed up :meth:`int.from_bytes` when passed a bytes-like object such as a
:class:`bytearray`.
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Suggested change
Speed up:meth:`int.from_bytes` when passed a bytes-like object such as a
:class:`bytearray`.
Speed up:meth:`int.from_bytes` when passed a bytes-like object such as
:class:`bytes` and:class:`bytearray`.

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I do not think that it affectsbytes.

29 changes: 21 additions & 8 deletionsObjects/longobject.c
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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 +6453,26 @@ 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 (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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