}
-/* Overview of bmerge variables:
-**
-** list1 and list2 address the main and auxiliary arrays.
-** They swap identities after each merge pass.
-** Base points to the original list1, so we can tell if
-** the pointers ended up where they belonged (or must be copied).
-**
-** When we are merging two lists, f1 and f2 are the next elements
-** on the respective lists. l1 and l2 mark the end of the lists.
-** tp2 is the current location in the merged list.
-**
-** p1 records where f1 started.
-** After the merge, a new descriptor is built there.
-**
-** p2 is a ``parallel'' pointer in (what starts as) descriptor space.
-** It is used to identify and delimit the runs.
-**
-** In the heat of determining where q, the greater of the f1/f2 elements,
-** belongs in the other list, b, t and p, represent bottom, top and probe
-** locations, respectively, in the other list.
-** They make convenient temporary pointers in other places.
-*/
-
-STATIC void
-S_mergesortsv(pTHX_ gptr *list1, size_t nmemb, SVCOMPARE_t cmp)
-{
- int i, run;
- int sense;
- register gptr *f1, *f2, *t, *b, *p, *tp2, *l1, *l2, *q;
- gptr *aux, *list2, *p2, *last;
- gptr *base = list1;
- gptr *p1;
- gptr small[SMALLSORT];
-
- if (nmemb <= 1) return; /* sorted trivially */
- if (nmemb <= SMALLSORT) list2 = small; /* use stack for aux array */
- else { New(799,list2,nmemb,gptr); } /* allocate auxilliary array */
- aux = list2;
- dynprep(aTHX_ list1, list2, nmemb, cmp);
- last = PINDEX(list2, nmemb);
- while (NEXT(list2) != last) {
- /* More than one run remains. Do some merging to reduce runs. */
- l2 = p1 = list1;
- for (tp2 = p2 = list2; p2 != last;) {
- /* The new first run begins where the old second list ended.
- ** Use the p2 ``parallel'' pointer to identify the end of the run.
- */
- f1 = l2;
- t = NEXT(p2);
- f2 = l1 = POTHER(t, list2, list1);
- if (t != last) t = NEXT(t);
- l2 = POTHER(t, list2, list1);
- p2 = t;
- while (f1 < l1 && f2 < l2) {
- /* If head 1 is larger than head 2, find ALL the elements
- ** in list 2 strictly less than head1, write them all,
- ** then head 1. Then compare the new heads, and repeat,
- ** until one or both lists are exhausted.
- **
- ** In all comparisons (after establishing
- ** which head to merge) the item to merge
- ** (at pointer q) is the first operand of
- ** the comparison. When we want to know
- ** if ``q is strictly less than the other'',
- ** we can't just do
- ** cmp(q, other) < 0
- ** because stability demands that we treat equality
- ** as high when q comes from l2, and as low when
- ** q was from l1. So we ask the question by doing
- ** cmp(q, other) <= sense
- ** and make sense == 0 when equality should look low,
- ** and -1 when equality should look high.
- */
-
-
- if (cmp(aTHX_ *f1, *f2) <= 0) {
- q = f2; b = f1; t = l1;
- sense = -1;
- } else {
- q = f1; b = f2; t = l2;
- sense = 0;
- }
-
-
- /* ramp up
- **
- ** Leave t at something strictly
- ** greater than q (or at the end of the list),
- ** and b at something strictly less than q.
- */
- for (i = 1, run = 0 ;;) {
- if ((p = PINDEX(b, i)) >= t) {
- /* off the end */
- if (((p = PINDEX(t, -1)) > b) &&
- (cmp(aTHX_ *q, *p) <= sense))
- t = p;
- else b = p;
- break;
- } else if (cmp(aTHX_ *q, *p) <= sense) {
- t = p;
- break;
- } else b = p;
- if (++run >= RTHRESH) i += i;
- }
-
-
- /* q is known to follow b and must be inserted before t.
- ** Increment b, so the range of possibilities is [b,t).
- ** Round binary split down, to favor early appearance.
- ** Adjust b and t until q belongs just before t.
- */
-
- b++;
- while (b < t) {
- p = PINDEX(b, (PNELEM(b, t) - 1) / 2);
- if (cmp(aTHX_ *q, *p) <= sense) {
- t = p;
- } else b = p + 1;
- }
-
-
- /* Copy all the strictly low elements */
-
- if (q == f1) {
- FROMTOUPTO(f2, tp2, t);
- *tp2++ = *f1++;
- } else {
- FROMTOUPTO(f1, tp2, t);
- *tp2++ = *f2++;
- }
- }
-
-
- /* Run out remaining list */
- if (f1 == l1) {
- if (f2 < l2) FROMTOUPTO(f2, tp2, l2);
- } else FROMTOUPTO(f1, tp2, l1);
- p1 = NEXT(p1) = POTHER(tp2, list2, list1);
- }
- t = list1;
- list1 = list2;
- list2 = t;
- last = PINDEX(list2, nmemb);
- }
- if (base == list2) {
- last = PINDEX(list1, nmemb);
- FROMTOUPTO(list1, list2, last);
- }
- if (aux != small) Safefree(aux); /* free iff allocated */
- return;
-}
-
-
-/* What perl needs (least) is another sort implementation in the core.
- * So what's the story? The short (by jpl's standards) story is that
- * the merge sort above, in use since 5.7, is as fast as, or faster than,
+/* The original merge sort, in use since 5.7, was as fast as, or faster than,
* qsort on many platforms, but slower than qsort, conspicuously so,
- * on others. The most likely explanation is platform-specific
+ * on others. The most likely explanation was platform-specific
* differences in cache sizes and relative speeds.
*
* The quicksort divide-and-conquer algorithm guarantees that, as the
* many levels of cache exist, quicksort will "find" them, and,
* as long as smaller is faster, take advanatge of them.
*
- * By contrast, consider how the quicksort algorithm above works.
+ * By contrast, consider how the original mergesort algorithm worked.
* Suppose we have five runs (each typically of length 2 after dynprep).
*
* pass base aux
* The actual cache-friendly implementation will use a pseudo-stack
* to avoid recursion, and will unroll processing of runs of length 2,
* but it is otherwise similar to the recursive implementation.
- * If it's as good as the original mergesort implementation on all
- * platforms, it should replace that implementation. For benchmarking,
- * though, it is convenient to have both implementations available.
*/
typedef struct {
} off_runs; /* pseudo-stack element */
STATIC void
-S_cfmergesortsv(pTHX_ gptr *base, size_t nmemb, SVCOMPARE_t cmp)
+S_mergesortsv(pTHX_ gptr *base, size_t nmemb, SVCOMPARE_t cmp)
{
IV i, run, runs, offset;
I32 sense, level;
sortsvp = S_qsortsv;
else {
if (hints & HINT_SORT_MERGESORT)
- sortsvp = S_cfmergesortsv;
+ sortsvp = S_mergesortsv;
else
sortsvp = S_mergesortsv;
}
projects / p5sagit/p5-mst-13.2.git / commitdiff