Cleanup yielding a small speed boost: before rich comparisons were
introduced, list.sort() was rewritten to use only the "< or not <?"
distinction. After rich comparisons were introduced, docompare() was
fiddled to translate a Py_LT Boolean result into the old "-1 for <,
0 for ==, 1 for >" flavor of outcome, and the sorting code was left
alone. This left things more obscure than they should be, and turns
out it also cost measurable cycles.
So: The old CMPERROR novelty is gone. docompare() is renamed to islt(),
and now has the same return conditinos as PyObject_RichCompareBool. The
SETK macro is renamed to ISLT, and is even weirder than before (don't
complain unless you want to maintain the sort code <wink>).
Overall, this yields a 1-2% speedup in the usual (no explicit function
passed to list.sort()) case when sorting arrays of floats (as sortperf.py
does). The boost is higher for arrays of ints.
diff --git a/Objects/listobject.c b/Objects/listobject.c
index ce78fff..f2132b4 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -758,39 +758,28 @@
/* New quicksort implementation for arrays of object pointers.
Thanks to discussions with Tim Peters. */
-/* CMPERROR is returned by our comparison function when an error
- occurred. This is the largest negative integer (0x80000000 on a
- 32-bit system). */
-#define CMPERROR ( (int) ((unsigned int)1 << (8*sizeof(int) - 1)) )
-
/* Comparison function. Takes care of calling a user-supplied
comparison function (any callable Python object). Calls the
- standard comparison function, PyObject_Compare(), if the user-
- supplied function is NULL. */
+ standard comparison function, PyObject_RichCompareBool(), if the user-
+ supplied function is NULL.
+ Returns <0 on error, >0 if x < y, 0 if x >= y. */
static int
-docompare(PyObject *x, PyObject *y, PyObject *compare)
+islt(PyObject *x, PyObject *y, PyObject *compare)
{
PyObject *res;
PyObject *args;
int i;
- if (compare == NULL) {
- /* NOTE: we rely on the fact here that the sorting algorithm
- only ever checks whether k<0, i.e., whether x<y. So we
- invoke the rich comparison function with Py_LT ('<'), and
- return -1 when it returns true and 0 when it returns
- false. */
- i = PyObject_RichCompareBool(x, y, Py_LT);
- if (i < 0)
- return CMPERROR;
- else
- return -i;
- }
+ if (compare == NULL)
+ return PyObject_RichCompareBool(x, y, Py_LT);
+ /* Call the user's comparison function and translate the 3-way
+ * result into true or false (or error).
+ */
args = PyTuple_New(2);
if (args == NULL)
- return CMPERROR;
+ return -1;
Py_INCREF(x);
Py_INCREF(y);
PyTuple_SET_ITEM(args, 0, x);
@@ -798,20 +787,16 @@
res = PyObject_Call(compare, args, NULL);
Py_DECREF(args);
if (res == NULL)
- return CMPERROR;
+ return -1;
if (!PyInt_Check(res)) {
Py_DECREF(res);
PyErr_SetString(PyExc_TypeError,
"comparison function must return int");
- return CMPERROR;
+ return -1;
}
i = PyInt_AsLong(res);
Py_DECREF(res);
- if (i < 0)
- return -1;
- if (i > 0)
- return 1;
- return 0;
+ return i < 0;
}
/* MINSIZE is the smallest array that will get a full-blown samplesort
@@ -850,17 +835,21 @@
exactly in two. */
#define STACKSIZE 60
-
-#define SETK(X,Y) if ((k = docompare(X,Y,compare))==CMPERROR) goto fail
+/* Compare X to Y via islt(). Goto "fail" if the comparison raises an
+ error. Else "k" is set to true iff X<Y, and an "if (k)" block is
+ started. It makes more sense in context <wink>. X and Y are PyObject*s.
+*/
+#define IFLT(X, Y) if ((k = islt(X, Y, compare)) < 0) goto fail; \
+ if (k)
/* binarysort is the best method for sorting small arrays: it does
few compares, but can do data movement quadratic in the number of
elements.
[lo, hi) is a contiguous slice of a list, and is sorted via
- binary insertion.
+ binary insertion. This sort is stable.
On entry, must have lo <= start <= hi, and that [lo, start) is already
sorted (pass start == lo if you don't know!).
- If docompare complains (returns CMPERROR) return -1, else 0.
+ If islt() complains return -1, else 0.
Even in case of error, the output slice will be some permutation of
the input (nothing is lost or duplicated).
*/
@@ -869,12 +858,12 @@
binarysort(PyObject **lo, PyObject **hi, PyObject **start, PyObject *compare)
/* compare -- comparison function object, or NULL for default */
{
- /* assert lo <= start <= hi
- assert [lo, start) is sorted */
register int k;
register PyObject **l, **p, **r;
register PyObject *pivot;
+ assert(lo <= start && start <= hi);
+ /* assert [lo, start) is sorted */
if (lo == start)
++start;
for (; start < hi; ++start) {
@@ -884,8 +873,7 @@
pivot = *r;
do {
p = l + ((r - l) >> 1);
- SETK(pivot, *p);
- if (k < 0)
+ IFLT(pivot, *p)
r = p;
else
l = p + 1;
@@ -906,7 +894,7 @@
/* samplesortslice is the sorting workhorse.
[lo, hi) is a contiguous slice of a list, to be sorted in place.
On entry, must have lo <= hi,
- If docompare complains (returns CMPERROR) return -1, else 0.
+ If islt() complains return -1, else 0.
Even in case of error, the output slice will be some permutation of
the input (nothing is lost or duplicated).
@@ -1023,8 +1011,7 @@
*/
/* assert lo < hi */
for (r = lo+1; r < hi; ++r) {
- SETK(*r, *(r-1));
- if (k < 0)
+ IFLT(*r, *(r-1))
break;
}
/* [lo,r) is sorted, [r,hi) unknown. Get out cheap if there are
@@ -1036,8 +1023,7 @@
benchmark-driven silliness <wink>. */
/* assert lo < hi */
for (r = lo+1; r < hi; ++r) {
- SETK(*(r-1), *r);
- if (k < 0)
+ IFLT(*(r-1), *r)
break;
}
if (hi - r <= MAXMERGE) {
@@ -1192,8 +1178,7 @@
do {
/* slide l right, looking for key >= pivot */
do {
- SETK(*l, pivot);
- if (k < 0)
+ IFLT(*l, pivot)
++l;
else
break;
@@ -1202,8 +1187,7 @@
/* slide r left, looking for key < pivot */
while (l < r) {
register PyObject *rval = *r--;
- SETK(rval, pivot);
- if (k < 0) {
+ IFLT(rval, pivot) {
/* swap and advance */
r[1] = *l;
*l++ = rval;
@@ -1219,8 +1203,7 @@
everything to the right of r is >= pivot */
if (l == r) {
- SETK(*r, pivot);
- if (k < 0)
+ IFLT(*r, pivot)
++l;
else
--r;
@@ -1249,8 +1232,7 @@
*/
while (l < hi) {
/* pivot <= *l known */
- SETK(pivot, *l);
- if (k < 0)
+ IFLT(pivot, *l)
break;
else
/* <= and not < implies == */
@@ -1290,7 +1272,7 @@
return -1;
}
-#undef SETK
+#undef IFLT
static PyTypeObject immutable_list_type;