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gh-102221: Optimize math.lcm() for multiple arguments (recursive) #135554

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gh-102221: Optimize math.lcm() for multiple arguments (recursive) #135554

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64 changes: 37 additions & 27 deletions Modules/mathmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -788,6 +788,39 @@ long_lcm(PyObject *a, PyObject *b)
return ab;
}

static PyObject *
long_array_lcm(PyObject * const *args, Py_ssize_t args_length)
{
if (args_length == 1) {
return PyNumber_Index(args[0]);
}

PyObject *left, *right;
if (args_length == 2) {
left = PyNumber_Index(args[0]);
if (left == NULL) {
return NULL;
}
right = PyNumber_Index(args[1]);
}
else {
Py_ssize_t half = args_length / 2;
left = long_array_lcm(args, half);
if (left == NULL) {
return NULL;
}
right = long_array_lcm(args + half, args_length - half);
}
if (right == NULL) {
Py_DECREF(left);
return NULL;
}
PyObject *res = long_lcm(left, right);
Py_DECREF(left);
Py_DECREF(right);
return res;
}


/*[clinic input]
math.lcm
Expand All @@ -802,41 +835,18 @@ math_lcm_impl(PyObject *module, PyObject * const *args,
Py_ssize_t args_length)
/*[clinic end generated code: output=c8a59a5c2e55c816 input=3e4f4b7cdf948a98]*/
{
PyObject *res, *x;
Py_ssize_t i;

if (args_length == 0) {
return PyLong_FromLong(1);
}
res = PyNumber_Index(args[0]);
if (res == NULL) {
return NULL;
}
if (args_length == 1) {
Py_SETREF(res, PyNumber_Absolute(res));
return res;
}

PyObject *zero = _PyLong_GetZero(); // borrowed ref
for (i = 1; i < args_length; i++) {
x = PyNumber_Index(args[i]);
if (x == NULL) {
Py_DECREF(res);
return NULL;
}
if (res == zero) {
/* Fast path: just check arguments.
It is okay to use identity comparison here. */
Py_DECREF(x);
continue;
}
Py_SETREF(res, long_lcm(res, x));
Py_DECREF(x);
PyObject *res = PyNumber_Index(args[0]);
if (res == NULL) {
return NULL;
}
Py_SETREF(res, PyNumber_Absolute(res));
return res;
}
return res;
return long_array_lcm(args, args_length);
}


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