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0db71e0fa9
This adds a generic bottom-up mergesort implementation for singly linked lists. It was inspired by Simon Tatham's webpage on the topic[1], but not so much by his implementation -- for no good reason, really, just a case of NIH. [1] http://www.chiark.greenend.org.uk/~sgtatham/algorithms/listsort.html Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx> Signed-off-by: Junio C Hamano <gitster@pobox.com>
74 lines
1.5 KiB
C
74 lines
1.5 KiB
C
#include "cache.h"
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#include "mergesort.h"
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struct mergesort_sublist {
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void *ptr;
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unsigned long len;
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};
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static void *get_nth_next(void *list, unsigned long n,
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void *(*get_next_fn)(const void *))
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{
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while (n-- && list)
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list = get_next_fn(list);
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return list;
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}
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static void *pop_item(struct mergesort_sublist *l,
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void *(*get_next_fn)(const void *))
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{
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void *p = l->ptr;
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l->ptr = get_next_fn(l->ptr);
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l->len = l->ptr ? (l->len - 1) : 0;
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return p;
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}
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void *mergesort(void *list,
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void *(*get_next_fn)(const void *),
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void (*set_next_fn)(void *, void *),
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int (*compare_fn)(const void *, const void *))
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{
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unsigned long l;
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if (!list)
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return NULL;
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for (l = 1; ; l *= 2) {
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void *curr;
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struct mergesort_sublist p, q;
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p.ptr = list;
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q.ptr = get_nth_next(p.ptr, l, get_next_fn);
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if (!q.ptr)
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break;
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p.len = q.len = l;
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if (compare_fn(p.ptr, q.ptr) > 0)
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list = curr = pop_item(&q, get_next_fn);
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else
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list = curr = pop_item(&p, get_next_fn);
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while (p.ptr) {
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while (p.len || q.len) {
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void *prev = curr;
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if (!p.len)
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curr = pop_item(&q, get_next_fn);
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else if (!q.len)
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curr = pop_item(&p, get_next_fn);
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else if (compare_fn(p.ptr, q.ptr) > 0)
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curr = pop_item(&q, get_next_fn);
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else
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curr = pop_item(&p, get_next_fn);
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set_next_fn(prev, curr);
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}
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p.ptr = q.ptr;
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p.len = l;
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q.ptr = get_nth_next(p.ptr, l, get_next_fn);
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q.len = q.ptr ? l : 0;
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}
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set_next_fn(curr, NULL);
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}
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return list;
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}
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