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bpo-24076: Inline single digit unpacking in the integer fastpath of sum() #28469

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Sep 21, 2021
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bpo-24076: Inline single digit unpacking in the integer fastpath of sum() #28469

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bpo-24076: Inline single digit unpacking in the integer fastpath of s…
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2021-09-20-10-02-12.bpo-24076.ZFgFSj.rst
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@@ -0,0 +1 @@
sum() was further optimised for summing up single digit integers.
10 changes: 9 additions & 1 deletion Python/bltinmodule.c
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Expand Up @@ -2479,7 +2479,15 @@ builtin_sum_impl(PyObject *module, PyObject *iterable, PyObject *start)
return PyLong_FromLong(i_result);
}
if (PyLong_CheckExact(item) || PyBool_Check(item)) {
long b = PyLong_AsLongAndOverflow(item, &overflow);
long b;
overflow = 0;
/* Single digits are common, fast, and cannot overflow on unpacking. */
switch (Py_SIZE(item)) {
case -1: b = -(sdigit) ((PyLongObject*)item)->ob_digit[0]; break;
case 0: continue;
case 1: b = ((PyLongObject*)item)->ob_digit[0]; break;
default: b = PyLong_AsLongAndOverflow(item, &overflow); break;
}
if (overflow == 0 &&
(i_result >= 0 ? (b <= LONG_MAX - i_result)
: (b >= LONG_MIN - i_result)))
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