add mergesort() for linked lists

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>
pull/20/head
René Scharfe 11 years ago committed by Junio C Hamano
parent 828ea97de4
commit 0db71e0fa9
  1. 1
      .gitignore
  2. 3
      Makefile
  3. 73
      mergesort.c
  4. 9
      mergesort.h
  5. 52
      test-mergesort.c

1
.gitignore vendored

@ -180,6 +180,7 @@
/test-index-version
/test-line-buffer
/test-match-trees
/test-mergesort
/test-mktemp
/test-obj-pool
/test-parse-options

@ -465,6 +465,7 @@ TEST_PROGRAMS_NEED_X += test-genrandom
TEST_PROGRAMS_NEED_X += test-index-version
TEST_PROGRAMS_NEED_X += test-line-buffer
TEST_PROGRAMS_NEED_X += test-match-trees
TEST_PROGRAMS_NEED_X += test-mergesort
TEST_PROGRAMS_NEED_X += test-mktemp
TEST_PROGRAMS_NEED_X += test-obj-pool
TEST_PROGRAMS_NEED_X += test-parse-options
@ -578,6 +579,7 @@ LIB_H += log-tree.h
LIB_H += mailmap.h
LIB_H += merge-file.h
LIB_H += merge-recursive.h
LIB_H += mergesort.h
LIB_H += notes.h
LIB_H += notes-cache.h
LIB_H += notes-merge.h
@ -681,6 +683,7 @@ LIB_OBJS += mailmap.o
LIB_OBJS += match-trees.o
LIB_OBJS += merge-file.o
LIB_OBJS += merge-recursive.o
LIB_OBJS += mergesort.o
LIB_OBJS += name-hash.o
LIB_OBJS += notes.o
LIB_OBJS += notes-cache.o

@ -0,0 +1,73 @@
#include "cache.h"
#include "mergesort.h"
struct mergesort_sublist {
void *ptr;
unsigned long len;
};
static void *get_nth_next(void *list, unsigned long n,
void *(*get_next_fn)(const void *))
{
while (n-- && list)
list = get_next_fn(list);
return list;
}
static void *pop_item(struct mergesort_sublist *l,
void *(*get_next_fn)(const void *))
{
void *p = l->ptr;
l->ptr = get_next_fn(l->ptr);
l->len = l->ptr ? (l->len - 1) : 0;
return p;
}
void *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;
p.ptr = list;
q.ptr = get_nth_next(p.ptr, l, get_next_fn);
if (!q.ptr)
break;
p.len = q.len = l;
if (compare_fn(p.ptr, q.ptr) > 0)
list = curr = pop_item(&q, get_next_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);
}
return list;
}

@ -0,0 +1,9 @@
#ifndef MERGESORT_H
#define MERGESORT_H
void *mergesort(void *list,
void *(*get_next_fn)(const void *),
void (*set_next_fn)(void *, void *),
int (*compare_fn)(const void *, const void *));
#endif

@ -0,0 +1,52 @@
#include "cache.h"
#include "mergesort.h"
struct line {
char *text;
struct line *next;
};
static void *get_next(const void *a)
{
return ((const struct line *)a)->next;
}
static void set_next(void *a, void *b)
{
((struct line *)a)->next = b;
}
static int compare_strings(const void *a, const void *b)
{
const struct line *x = a, *y = b;
return strcmp(x->text, y->text);
}
int main(int argc, const char **argv)
{
struct line *line, *p = NULL, *lines = NULL;
struct strbuf sb = STRBUF_INIT;
for (;;) {
if (strbuf_getwholeline(&sb, stdin, '\n'))
break;
line = xmalloc(sizeof(struct line));
line->text = strbuf_detach(&sb, NULL);
if (p) {
line->next = p->next;
p->next = line;
} else {
line->next = NULL;
lines = line;
}
p = line;
}
lines = mergesort(lines, get_next, set_next, compare_strings);
while (lines) {
printf("%s", lines->text);
lines = lines->next;
}
return 0;
}
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