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bpo-46055: Streamline inner loop for right shifts (#30243)

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Mark Dickinson 2021-12-27 18:04:36 +00:00 committed by GitHub
parent 2e3e0d23ad
commit 360fedc2d2
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1 changed files with 8 additions and 7 deletions
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15
Objects/longobject.c
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@ -4491,7 +4491,7 @@ long_rshift1(PyLongObject *a, Py_ssize_t wordshift, digit remshift)
{ {
PyLongObject *z = NULL; PyLongObject *z = NULL;
Py_ssize_t newsize, hishift, i, j; Py_ssize_t newsize, hishift, i, j;
digit lomask, himask; twodigits accum;
if (Py_SIZE(a) < 0) { if (Py_SIZE(a) < 0) {
/* Right shifting negative numbers is harder */ /* Right shifting negative numbers is harder */
@ -4511,16 +4511,17 @@ long_rshift1(PyLongObject *a, Py_ssize_t wordshift, digit remshift)
if (newsize <= 0) if (newsize <= 0)
return PyLong_FromLong(0); return PyLong_FromLong(0);
hishift = PyLong_SHIFT - remshift; hishift = PyLong_SHIFT - remshift;
lomask = ((digit)1 << hishift) - 1;
himask = PyLong_MASK ^ lomask;
z = _PyLong_New(newsize); z = _PyLong_New(newsize);
if (z == NULL) if (z == NULL)
return NULL; return NULL;
for (i = 0, j = wordshift; i < newsize; i++, j++) { j = wordshift;
z->ob_digit[i] = (a->ob_digit[j] >> remshift) & lomask; accum = a->ob_digit[j++] >> remshift;
if (i+1 < newsize) for (i = 0; j < Py_SIZE(a); i++, j++) {
z->ob_digit[i] |= (a->ob_digit[j+1] << hishift) & himask; accum |= (twodigits)a->ob_digit[j] << hishift;
z->ob_digit[i] = (digit)(accum & PyLong_MASK);
accum >>= PyLong_SHIFT;
} }
z->ob_digit[i] = (digit)accum;
z = maybe_small_long(long_normalize(z)); z = maybe_small_long(long_normalize(z));
} }
return (PyObject *)z; return (PyObject *)z;