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bpo-34151: Improve performance of some list operations (GH-8332)

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This commit is contained in:
Sergey Fedoseev 2018-08-11 18:12:07 +05:00 • committed by Xiang Zhang
parent 9e84084851
commit 2fc46979b8
2 changed files with 37 additions and 14 deletions
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2
Misc/NEWS.d/next/Core and Builtins/2018-07-25-20-26-02.bpo-34151.Q2pK9Q.rst Normal file
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@ -0,0 +1,2 @@
Performance of list concatenation, repetition and slicing operations is
slightly improved. Patch by Sergey Fedoseev.

35
Objects/listobject.c
View file

@ -180,6 +180,23 @@ PyList_New(Py_ssize_t size)
return (PyObject *) op; return (PyObject *) op;
} }
static PyObject *
list_new_prealloc(Py_ssize_t size)
{
PyListObject *op = (PyListObject *) PyList_New(0);
if (size == 0 || op == NULL) {
return (PyObject *) op;
}
assert(op->ob_item == NULL);
op->ob_item = PyMem_New(PyObject *, size);
if (op->ob_item == NULL) {
Py_DECREF(op);
return PyErr_NoMemory();
}
op->allocated = size;
return (PyObject *) op;
}
Py_ssize_t Py_ssize_t
PyList_Size(PyObject *op) PyList_Size(PyObject *op)
{ {
@ -438,7 +455,7 @@ list_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh)
else if (ihigh > Py_SIZE(a)) else if (ihigh > Py_SIZE(a))
ihigh = Py_SIZE(a); ihigh = Py_SIZE(a);
len = ihigh - ilow; len = ihigh - ilow;
np = (PyListObject *) PyList_New(len); np = (PyListObject *) list_new_prealloc(len);
if (np == NULL) if (np == NULL)
return NULL; return NULL;
@ -449,6 +466,7 @@ list_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh)
Py_INCREF(v); Py_INCREF(v);
dest[i] = v; dest[i] = v;
} }
Py_SIZE(np) = len;
return (PyObject *)np; return (PyObject *)np;
} }
@ -479,7 +497,7 @@ list_concat(PyListObject *a, PyObject *bb)
if (Py_SIZE(a) > PY_SSIZE_T_MAX - Py_SIZE(b)) if (Py_SIZE(a) > PY_SSIZE_T_MAX - Py_SIZE(b))
return PyErr_NoMemory(); return PyErr_NoMemory();
size = Py_SIZE(a) + Py_SIZE(b); size = Py_SIZE(a) + Py_SIZE(b);
np = (PyListObject *) PyList_New(size); np = (PyListObject *) list_new_prealloc(size);
if (np == NULL) { if (np == NULL) {
return NULL; return NULL;
} }
@ -497,6 +515,7 @@ list_concat(PyListObject *a, PyObject *bb)
Py_INCREF(v); Py_INCREF(v);
dest[i] = v; dest[i] = v;
} }
Py_SIZE(np) = size;
return (PyObject *)np; return (PyObject *)np;
#undef b #undef b
} }
@ -516,19 +535,19 @@ list_repeat(PyListObject *a, Py_ssize_t n)
size = Py_SIZE(a) * n; size = Py_SIZE(a) * n;
if (size == 0) if (size == 0)
return PyList_New(0); return PyList_New(0);
np = (PyListObject *) PyList_New(size); np = (PyListObject *) list_new_prealloc(size);
if (np == NULL) if (np == NULL)
return NULL; return NULL;
items = np->ob_item;
if (Py_SIZE(a) == 1) { if (Py_SIZE(a) == 1) {
items = np->ob_item;
elem = a->ob_item[0]; elem = a->ob_item[0];
for (i = 0; i < n; i++) { for (i = 0; i < n; i++) {
items[i] = elem; items[i] = elem;
Py_INCREF(elem); Py_INCREF(elem);
} }
return (PyObject *) np;
} }
else {
p = np->ob_item; p = np->ob_item;
items = a->ob_item; items = a->ob_item;
for (i = 0; i < n; i++) { for (i = 0; i < n; i++) {
@ -538,6 +557,8 @@ list_repeat(PyListObject *a, Py_ssize_t n)
p++; p++;
} }
} }
}
Py_SIZE(np) = size;
return (PyObject *) np; return (PyObject *) np;
} }
@ -2738,7 +2759,7 @@ list_subscript(PyListObject* self, PyObject* item)
return list_slice(self, start, stop); return list_slice(self, start, stop);
} }
else { else {
result = PyList_New(slicelength); result = list_new_prealloc(slicelength);
if (!result) return NULL; if (!result) return NULL;
src = self->ob_item; src = self->ob_item;
@ -2749,7 +2770,7 @@ list_subscript(PyListObject* self, PyObject* item)
Py_INCREF(it); Py_INCREF(it);
dest[i] = it; dest[i] = it;
} }
Py_SIZE(result) = slicelength;
return result; return result;
} }
} }