From: "René Scharfe" <l.s.r@web.de>
To: Git List <git@vger.kernel.org>
Cc: Junio C Hamano <gitster@pobox.com>
Subject: [PATCH 02/10] mergesort: tighten merge loop
Date: Sat, 16 Jul 2022 18:53:45 +0200 [thread overview]
Message-ID: <df2d020d-29e2-6b6b-bde7-576fc1b9c883@web.de> (raw)
In-Reply-To: <4d7cd286-398e-215c-f2bd-aa7e8207be4f@web.de>
llist_merge() has special inner loops for taking elements from either of
the two lists to merge. That helps consistently preferring one over the
other, for stability. Merge the loops, swap the lists when the other
one has the next element for the result and keep track on which one to
prefer on equality. This results in shorter code and object text:
Before:
__TEXT __DATA __OBJC others dec hex
412 0 0 3441 3853 f0d mergesort.o
With this patch:
__TEXT __DATA __OBJC others dec hex
352 0 0 3516 3868 f1c mergesort.o
Performance doesn't get worse:
Before:
0071.12: llist_mergesort() unsorted 0.24(0.22+0.01)
0071.14: llist_mergesort() sorted 0.12(0.10+0.01)
0071.16: llist_mergesort() reversed 0.12(0.10+0.01)
Benchmark 1: t/helper/test-tool mergesort test
Time (mean ± σ): 109.2 ms ± 0.2 ms [User: 107.5 ms, System: 1.1 ms]
Range (min … max): 108.9 ms … 109.6 ms 27 runs
With this patch:
0071.12: llist_mergesort() unsorted 0.24(0.22+0.01)
0071.14: llist_mergesort() sorted 0.12(0.10+0.01)
0071.16: llist_mergesort() reversed 0.12(0.10+0.01)
Benchmark 1: t/helper/test-tool mergesort test
Time (mean ± σ): 108.4 ms ± 0.2 ms [User: 106.7 ms, System: 1.2 ms]
Range (min … max): 108.0 ms … 108.8 ms 27 runs
Signed-off-by: René Scharfe <l.s.r@web.de>
---
mergesort.c | 19 ++++++-------------
1 file changed, 6 insertions(+), 13 deletions(-)
diff --git a/mergesort.c b/mergesort.c
index 92150c4101..6bda3a1c0e 100644
--- a/mergesort.c
+++ b/mergesort.c
@@ -8,10 +8,11 @@ static void *llist_merge(void *list, void *other,
int (*compare_fn)(const void *, const void *))
{
void *result = list, *tail;
+ int prefer_list = compare_fn(list, other) <= 0;
- if (compare_fn(list, other) > 0) {
+ if (!prefer_list) {
result = other;
- goto other;
+ SWAP(list, other);
}
for (;;) {
do {
@@ -21,18 +22,10 @@ static void *llist_merge(void *list, void *other,
set_next_fn(tail, other);
return result;
}
- } while (compare_fn(list, other) <= 0);
+ } while (compare_fn(list, other) < prefer_list);
set_next_fn(tail, other);
- other:
- do {
- tail = other;
- other = get_next_fn(other);
- if (!other) {
- set_next_fn(tail, list);
- return result;
- }
- } while (compare_fn(list, other) > 0);
- set_next_fn(tail, list);
+ prefer_list ^= 1;
+ SWAP(list, other);
}
}
--
2.37.1
next prev parent reply other threads:[~2022-07-16 16:53 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-16 16:50 [PATCH 00/10] typed sort of linked lists René Scharfe
2022-07-16 16:52 ` [PATCH 01/10] mergesort: unify ranks loops René Scharfe
2022-07-16 16:53 ` René Scharfe [this message]
2022-07-16 16:54 ` [PATCH 03/10] mergesort: add macros for typed sort of linked lists René Scharfe
2022-07-16 16:56 ` [PATCH 04/10] test-mergesort: use DEFINE_LIST_SORT_DEBUG René Scharfe
2022-07-16 16:57 ` [PATCH 05/10] test-mergesort: use DEFINE_LIST_SORT René Scharfe
2022-07-16 16:58 ` [PATCH 06/10] blame: " René Scharfe
2022-07-16 16:59 ` [PATCH 07/10] commit: " René Scharfe
2022-07-16 16:59 ` [PATCH 08/10] fetch-pack: " René Scharfe
2022-07-16 17:01 ` [PATCH 09/10] packfile: " René Scharfe
2022-07-16 17:02 ` [PATCH 10/10] mergesort: remove llist_mergesort() René Scharfe
2022-07-17 22:31 ` [PATCH 00/10] typed sort of linked lists Junio C Hamano
2022-07-25 18:52 ` Junio C Hamano
2022-07-25 20:35 ` Derrick Stolee
2022-07-25 20:49 ` Junio C Hamano
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