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git/mergesort.h

106 lines
2.9 KiB

#ifndef MERGESORT_H
#define MERGESORT_H
/* Combine two sorted lists. Take from `list` on equality. */
#define DEFINE_LIST_MERGE_INTERNAL(name, type) \
static type *name##__merge(type *list, type *other, \
int (*compare_fn)(const type *, const type *))\
{ \
type *result = list, *tail; \
int prefer_list = compare_fn(list, other) <= 0; \
\
if (!prefer_list) { \
result = other; \
SWAP(list, other); \
} \
for (;;) { \
do { \
tail = list; \
list = name##__get_next(list); \
if (!list) { \
name##__set_next(tail, other); \
return result; \
} \
} while (compare_fn(list, other) < prefer_list); \
name##__set_next(tail, other); \
prefer_list ^= 1; \
SWAP(list, other); \
} \
}
/*
* 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.
*/
#define DEFINE_LIST_SORT_INTERNAL(scope, name, type) \
scope void name(type **listp, \
int (*compare_fn)(const type *, const type *)) \
{ \
type *list = *listp; \
type *ranks[bitsizeof(type *)]; \
size_t n = 0; \
\
if (!list) \
return; \
\
for (;;) { \
int i; \
size_t m; \
type *next = name##__get_next(list); \
if (next) \
name##__set_next(list, NULL); \
for (i = 0, m = n;; i++, m >>= 1) { \
if (m & 1) { \
list = name##__merge(ranks[i], list, \
compare_fn); \
} else if (next) { \
break; \
} else if (!m) { \
*listp = list; \
return; \
} \
} \
n++; \
ranks[i] = list; \
list = next; \
} \
}
#define DECLARE_LIST_SORT(scope, name, type) \
scope void name(type **listp, \
int (*compare_fn)(const type *, const type *))
#define DEFINE_LIST_SORT_DEBUG(scope, name, type, next_member, \
on_get_next, on_set_next) \
\
static inline type *name##__get_next(const type *elem) \
{ \
on_get_next; \
return elem->next_member; \
} \
\
static inline void name##__set_next(type *elem, type *next) \
{ \
on_set_next; \
elem->next_member = next; \
} \
\
DEFINE_LIST_MERGE_INTERNAL(name, type) \
DEFINE_LIST_SORT_INTERNAL(scope, name, type) \
DECLARE_LIST_SORT(scope, name, type)
#define DEFINE_LIST_SORT(scope, name, type, next_member) \
DEFINE_LIST_SORT_DEBUG(scope, name, type, next_member, (void)0, (void)0)
#endif