From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: "René Scharfe" <l.s.r@web.de>
Cc: Git List <git@vger.kernel.org>, Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH 9/9] mergesort: use ranks stack
Date: Mon, 17 Jan 2022 18:43:08 +0100 [thread overview]
Message-ID: <220117.864k62qmt1.gmgdl@evledraar.gmail.com> (raw)
In-Reply-To: <636647b1-f666-f1e2-4127-ee0869b61036@web.de>
On Fri, Oct 01 2021, René Scharfe wrote:
> +/*
> + * Perform an iterative mergesort using an array of sublists.
> + *
> + * n is the number of items.
> + * ranks[i] is undefined if n & 2^i == 0, and assumed empty.
> + * ranks[i] contains a sublist of length 2^i otherwise.
> + *
> + * The number of bits in a void pointer limits the number of objects
> + * that can be created, and thus the number of array elements necessary
> + * to be able to sort any valid list.
> + *
> + * Adding an item to this array is like incrementing a binary number;
> + * positional values for set bits correspond to sublist lengths.
> + */
> void *llist_mergesort(void *list,
> void *(*get_next_fn)(const void *),
> void (*set_next_fn)(void *, void *),
> int (*compare_fn)(const void *, const void *))
> {
> - unsigned long l;
> -
> - if (!list)
> - return NULL;
> - for (l = 1; ; l *= 2) {
> - void *curr;
> - struct mergesort_sublist p, q;
> + void *ranks[bitsizeof(void *)];
> + size_t n = 0;
> + int i;
>
> - p.ptr = list;
> - q.ptr = get_nth_next(p.ptr, l, get_next_fn);
> - if (!q.ptr)
> - break;
> - p.len = q.len = l;
> + while (list) {
> + void *next = get_next_fn(list);
> + if (next)
> + set_next_fn(list, NULL);
> + for (i = 0; n & (1 << i); i++)
> + list = llist_merge(ranks[i], list, get_next_fn,
> + set_next_fn, compare_fn);
> + n++;
> + ranks[i] = list;
> + list = next;
> + }
(Commenting on a commit integrated into v2.34.0)
The aCC compiler on HP/UX notes:
"mergesort.c", line 67: warning #2549-D: variable "ranks" is used before its value is set
list = llist_merge(ranks[i], list, get_next_fn,
It's commenting on the ranks[i] within the for-loop-within-while-loop
above.
>
> - if (compare_fn(p.ptr, q.ptr) > 0)
> - list = curr = pop_item(&q, get_next_fn);
> + for (i = 0; n; i++, n >>= 1) {
> + if (!(n & 1))
> + continue;
> + if (list)
> + list = llist_merge(ranks[i], list, get_next_fn,
> + set_next_fn, compare_fn);
> else
> - list = curr = pop_item(&p, get_next_fn);
> -
> - while (p.ptr) {
> - while (p.len || q.len) {
> - void *prev = curr;
> -
> - if (!p.len)
> - curr = pop_item(&q, get_next_fn);
> - else if (!q.len)
> - curr = pop_item(&p, get_next_fn);
> - else if (compare_fn(p.ptr, q.ptr) > 0)
> - curr = pop_item(&q, get_next_fn);
> - else
> - curr = pop_item(&p, get_next_fn);
> - set_next_fn(prev, curr);
> - }
> - p.ptr = q.ptr;
> - p.len = l;
> - q.ptr = get_nth_next(p.ptr, l, get_next_fn);
> - q.len = q.ptr ? l : 0;
> -
> - }
> - set_next_fn(curr, NULL);
> + list = ranks[i];
> }
> return list;
> }
next prev parent reply other threads:[~2022-01-17 17:44 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-01 9:07 [PATCH 0/9] mergesort: improve tests and performance René Scharfe
2021-10-01 9:10 ` [PATCH 1/9] test-mergesort: use strbuf_getline() René Scharfe
2021-10-02 9:08 ` Ævar Arnfjörð Bjarmason
2021-10-02 16:56 ` René Scharfe
2021-10-01 9:11 ` [PATCH 2/9] test-mergesort: add sort subcommand René Scharfe
2021-10-01 20:26 ` Junio C Hamano
2021-10-01 9:12 ` [PATCH 3/9] test-mergesort: add test subcommand René Scharfe
2021-10-01 20:26 ` Junio C Hamano
2021-10-02 8:35 ` Ævar Arnfjörð Bjarmason
2021-10-03 10:15 ` René Scharfe
2021-10-03 17:33 ` Junio C Hamano
2021-10-07 20:00 ` René Scharfe
2021-10-08 4:04 ` [PATCH 10/9 v2] test-mergesort: use repeatable random numbers René Scharfe
2021-10-08 4:17 ` Jeff King
2021-10-08 7:23 ` Ævar Arnfjörð Bjarmason
2021-10-08 17:30 ` René Scharfe
2021-10-08 19:00 ` Ævar Arnfjörð Bjarmason
2021-10-03 10:15 ` [PATCH 3/9] test-mergesort: add test subcommand René Scharfe
2021-10-01 9:14 ` [PATCH 4/9] test-mergesort: add generate subcommand René Scharfe
2021-10-01 9:16 ` [PATCH 5/9] test-mergesort: add unriffle mode René Scharfe
2021-10-01 9:17 ` [PATCH 6/9] test-mergesort: add unriffle_skewed mode René Scharfe
2021-10-01 9:19 ` [PATCH 7/9] p0071: measure sorting of already sorted and reversed files René Scharfe
2021-10-01 9:19 ` [PATCH 8/9] p0071: test performance of llist_mergesort() René Scharfe
2021-10-01 9:22 ` [PATCH 9/9] mergesort: use ranks stack René Scharfe
2022-01-17 17:43 ` Ævar Arnfjörð Bjarmason [this message]
2022-01-17 18:22 ` René Scharfe
2022-01-18 5:07 ` René Scharfe
2022-01-18 10:40 ` Ævar Arnfjörð Bjarmason
2022-01-18 12:27 ` René Scharfe
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