Minor cleanup by Tim after my changes:

+ Took the "list" argument out of the other functions that no longer need
it.  This speeds things up a little more.

+ Small comment changes in accord with that.

+ Exploited the now-safe ability to cache values in the partitioning loop.
Makes no timing difference on my flavor of Pentium, but this machine ran out
of registers 12 iterations ago.  It should yield a small speedup on a RISC
machine, and not hurt in any case.

Objects/listobject.c

@@ -665,7 +665,7 @@ docompare(x, y, compare)
 /* 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 the list, and is sorted via
+   [lo, hi) is a contiguous slice of a list, and is sorted via
    binary insertion.
    On entry, must have lo <= start <= hi, and that [lo, start) is already
    sorted (pass start == lo if you don't know!).
@@ -675,11 +675,10 @@ docompare(x, y, compare)
 */
 
 static int
-binarysort(lo, hi, start, list, compare)
+binarysort(lo, hi, start, compare)
 	PyObject **lo;
 	PyObject **hi;
 	PyObject **start;
-	PyListObject *list; /* Needed by docompare for paranoia checks */
 	PyObject *compare;/* Comparison function object, or NULL for default */
 {
 	/* assert lo <= start <= hi
@@ -717,7 +716,7 @@ binarysort(lo, hi, start, list, compare)
 }
 
 /* samplesortslice is the sorting workhorse.
-   [lo, hi) is a contiguous slice of the list, to be sorted in place.
+   [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.
    Even in case of error, the output slice will be some permutation of
@@ -778,7 +777,7 @@ struct SamplesortStackNode {
 };
 
 /* The number of PPs we want is 2**k - 1, where 2**k is as close to
-   N / ln(N) as possible.  So k ~= lg(N / ln(N).  Calling libm routines
+   N / ln(N) as possible.  So k ~= lg(N / ln(N)).  Calling libm routines
    is undesirable, so cutoff values are canned in the "cutoff" table
    below:  cutoff[i] is the smallest N such that k == CUTOFFBASE + i. */
 #define CUTOFFBASE 4
@@ -810,10 +809,9 @@ static int cutoff[] = {
 };
 
 static int
-samplesortslice(lo, hi, list, compare)
+samplesortslice(lo, hi, compare)
 	PyObject **lo;
 	PyObject **hi;
-	PyListObject *list;  /* Needed by docompare for paranoia checks */
 	PyObject *compare;/* Comparison function object, or NULL for default */
 {
 	register PyObject **l, **r;
@@ -846,7 +844,7 @@ samplesortslice(lo, hi, list, compare)
 	/* [lo,r) is sorted, [r,hi) unknown.  Get out cheap if there are
 	   few unknowns, or few elements in total. */
 	if (hi - r <= MAXMERGE || n < MINSIZE)
-		return binarysort(lo, hi, r, list, compare);
+		return binarysort(lo, hi, r, compare);
 
 	/* Check for the array already being reverse-sorted.  Typical
 	   benchmark-driven silliness <wink>. */
@@ -865,7 +863,7 @@ samplesortslice(lo, hi, list, compare)
 			tmp = *l; *l = *r; *r = tmp;
 			++l;
 		} while (l < r);
-		return binarysort(lo, hi, originalr, list, compare);
+		return binarysort(lo, hi, originalr, compare);
 	}
 
 	/* ----------------------------------------------------------
@@ -907,7 +905,7 @@ samplesortslice(lo, hi, list, compare)
 	}
 
 	/* Recursively sort the preselected pivots. */
-	if (samplesortslice(lo, lo + extra, list, compare) < 0)
+	if (samplesortslice(lo, lo + extra, compare) < 0)
 		goto fail;
 
 	top = 0;          /* index of available stack slot */
@@ -932,8 +930,7 @@ samplesortslice(lo, hi, list, compare)
 				   This is rare, since the average size
 				   of a final block is only about
 				   ln(original n). */
-				if (samplesortslice(lo, hi, list,
-						    compare) < 0)
+				if (samplesortslice(lo, hi, compare) < 0)
 					goto fail;
 			}
 			else {
@@ -951,7 +948,7 @@ samplesortslice(lo, hi, list, compare)
 					} while (--k);
 				}
 				if (binarysort(lo - extra, hi, lo,
-					       list, compare) < 0)
+					       compare) < 0)
 					goto fail;
 			}
 
@@ -1024,18 +1021,14 @@ samplesortslice(lo, hi, list, compare)
 
 			/* slide r left, looking for key < pivot */
 			while (l < r) {
-				SETK(*r, pivot);
-				if (k < 0)
+				register PyObject *rval = *r--;
+				SETK(rval, pivot);
+				if (k < 0) {
+					/* swap and advance */
+					r[1] = *l;
+					*l++ = rval;
 					break;
-				else
-					--r;
-			}
-
-			/* swap and advance both pointers */
-			if (l < r) {
-				tmp = *l; *l = *r; *r = tmp;
-				++l;
-				--r;
+				}
 			}
 
 		} while (l < r);
@@ -1131,7 +1124,7 @@ listsort(self, compare)
 	self->ob_type = &immutable_list_type;
 	err = samplesortslice(self->ob_item,
 			      self->ob_item + self->ob_size,
-			      self, compare);
+			      compare);
 	self->ob_type = &PyList_Type;
 	if (err < 0)
 		return NULL;
@@ -1402,3 +1395,4 @@ static PyTypeObject immutable_list_type = {
 	&immutable_list_as_sequence,	/*tp_as_sequence*/
 	0,		/*tp_as_mapping*/
 };
+