linked_list_sort_eglib.c

/*
 * ***** BEGIN MIT LICENSE BLOCK *****
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * Author:
 *   Raja R Harinath (rharinath@novell.com)
 *
 * (C) 2006 Novell, Inc.
 *
 * ***** END MIT LICENSE BLOCK *****
 */

/**
 * Common implementation of linked-list sorting.
 *
 * Originally from Mono's eglib, adapted for portable reuse.
 *
 *
 * Source file including this must define:
 * - SORT_IMPL_LINKTYPE: Struct type for sorting.
 * - SORT_IMPL_LINKTYPE_DATA: Data pointer or leave undefined to pass the link.
 * - SORT_IMPL_FUNC: Function name of the sort function.
 *
 * Optionally:
 * - SORT_IMPL_USE_THUNK: Takes an argument for the sort function (like `qsort_r`).
 *
 *
 * -------------------------------------------------------------------- *
 * Example use:
 *
 * \code{.c}
 * // example struct
 * typedef struct LinkElem {
 *     struct LinkElem *next;
 *     void *data;
 * } LinkElem;
 *
 * #define SORT_IMPL_LINKTYPE LinkElem
 * #define SORT_IMPL_LINKTYPE_DATA data
 * 
 * // regular call
 * #define SORT_IMPL_FUNC linkelem_sort_fn
 * #include "list_sort_impl.h"
 * #undef SORT_IMPL_FUNC
 * 
 * // reentrant call
 * #define SORT_IMPL_USE_THUNK
 * #define SORT_IMPL_FUNC linkelem_sort_fn_r
 * #include "list_sort_impl.h"
 * #undef SORT_IMPL_FUNC
 * #undef SORT_IMPL_USE_THUNK
 * 
 * #undef SORT_IMPL_LINKTYPE
 * #undef SORT_IMPL_LINKTYPE_DATA
 *
 * // Expose externally
 * LinkElem list_sort(LinkElem *link, int (*cmp)(const void *, const void *))
 * {
 *     return linkelem_sort_fn(link, cmp);
 * }
 *
 * LinkElem list_sort_r(LinkElem *link, void *thunk, int (*cmp)(const void *, const void *))
 * {
 *     return linkelem_sort_fn(link, thunk, cmp);
 * }
 * \endcode
 */

#define _CONCAT_AUX(MACRO_ARG1, MACRO_ARG2) MACRO_ARG1 ## MACRO_ARG2
#define _CONCAT(MACRO_ARG1, MACRO_ARG2) _CONCAT_AUX(MACRO_ARG1, MACRO_ARG2)

#define _SORT_PREFIX(id) _CONCAT(SORT_IMPL_FUNC, _##id)

/* local identifiers */
#define SortInfo _SORT_PREFIX(SortInfo)
#define init_sort_info _SORT_PREFIX(init_sort_info)
#define merge_lists _SORT_PREFIX(merge_lists)
#define sweep_up _SORT_PREFIX(sweep_up)
#define insert_list _SORT_PREFIX(insert_list)
#define CompareFn _SORT_PREFIX(CompareFn)
#define digit _SORT_PREFIX(digit)

#define list_node SORT_IMPL_LINKTYPE
#define list_sort_do SORT_IMPL_FUNC

#ifdef SORT_IMPL_LINKTYPE_DATA
#  define SORT_ARG(n) ((n)->SORT_IMPL_LINKTYPE_DATA)
#else
#  define SORT_ARG(n) (n)
#endif

#ifdef SORT_IMPL_USE_THUNK
#  define THUNK_ARG(thunk) thunk,
#else
#  define THUNK_ARG(thunk)
#endif

typedef int (* CompareFn)(
#ifdef SORT_IMPL_USE_THUNK
        void *thunk,
#endif
        const void *,
        const void *);

/*
 * This code requires a typedef named 'list_node' for the list node.  It
 * is assumed that the list type is the type of a pointer to a list
 * node, and that the node has a field named 'next' that implements to
 * the linked list.  No additional invariant is maintained (e.g. the
 * 'prev' pointer of a doubly-linked list node is _not_ updated).  Any
 * invariant would require a post-processing pass to fix matters if
 * necessary.
 */
typedef list_node *digit;

/*
 * The maximum possible depth of the merge tree
 *   = ceiling(log2(maximum number of list nodes))
 *   = ceiling(log2(maximum possible memory size/size of each list node))
 *   = number of bits in 'size_t' - floor(log2(sizeof digit))
 * Also, each list in SortInfo is at least 2 nodes long: we can reduce the depth by 1
 */
#define FLOOR_LOG2(x) (((x) >= 2) + ((x) >= 4) + ((x) >= 8) + ((x) >= 16) + ((x) >= 32) + ((x) >= 64) + ((x) >= 128))
#define MAX_RANKS ((sizeof(size_t) * 8) - FLOOR_LOG2(sizeof(list_node)) - 1)

struct SortInfo {
	int min_rank, n_ranks;
	CompareFn func;

#ifdef SORT_IMPL_USE_THUNK
	void *thunk;
#endif

	/* Invariant: ranks[i] == NULL || length(ranks[i]) >= 2**(i+1) */
	list_node *ranks[MAX_RANKS]; /* ~ 128 bytes on 32bit, ~ 512 bytes on 64bit */
};

static inline void init_sort_info(
        struct SortInfo *si,
        CompareFn func
#ifdef SORT_IMPL_USE_THUNK
        , void *thunk
#endif
        )
{
	si->min_rank = si->n_ranks = 0;
	si->func = func;
	/* we don't need to initialize si->ranks, since we never lookup past si->n_ranks.  */

#ifdef SORT_IMPL_USE_THUNK
	si->thunk = thunk;
#endif
}

static inline list_node *merge_lists(
        list_node *first, list_node *second,
#ifdef SORT_IMPL_USE_THUNK
        void *thunk,
#endif
        CompareFn func)
{
	/* merge the two lists */
	list_node *list = NULL;
	list_node **pos = &list;
	while (first && second) {
		if (func(THUNK_ARG(thunk) SORT_ARG(first), SORT_ARG(second)) > 0) {
			*pos = second;
			second = second->next;
		}
		else {
			*pos = first;
			first = first->next;
		}
		pos = &((*pos)->next);
	}
	*pos = first ? first : second;
	return list;
}

/* Pre-condition: upto <= si->n_ranks, list == NULL || length(list) == 1 */
static inline list_node *sweep_up(struct SortInfo *si, list_node *list, int upto)
{
	int i;
	for (i = si->min_rank; i < upto; ++i) {
		list = merge_lists(si->ranks[i], list, THUNK_ARG(si->thunk) si->func);
		si->ranks[i] = NULL;
	}
	return list;
}

/*
 * The 'ranks' array essentially captures the recursion stack of a mergesort.
 * The merge tree is built in a bottom-up manner.  The control loop for
 * updating the 'ranks' array is analogous to incrementing a binary integer,
 * and the O(n) time for counting upto n translates to O(n) merges when
 * inserting rank-0 lists.  When we plug in the sizes of the lists involved in
 * those merges, we get the O(n log n) time for the sort.
 *
 * Inserting higher-ranked lists reduce the height of the merge tree, and also
 * eliminate a lot of redundant comparisons when merging two lists that would've
 * been part of the same run.  Adding a rank-i list is analogous to incrementing
 * a binary integer by 2**i in one operation, thus sharing a similar speedup.
 *
 * When inserting higher-ranked lists, we choose to clear out the lower ranks
 * in the interests of keeping the sort stable, but this makes analysis harder.
 * Note that clearing the lower-ranked lists is O(length(list))-- thus it
 * shouldn't affect the O(n log n) behaviour.  IOW, inserting one rank-i list
 * is equivalent to inserting 2**i rank-0 lists, thus even if we do i additional
 * merges in the clearing-out (taking at most 2**i time) we are still fine.
 */

/* Pre-condition: 2**(rank+1) <= length(list) < 2**(rank+2) (therefore: length(list) >= 2) */
static inline void insert_list(
        struct SortInfo *si,
        list_node *list,
        int rank)
{
	int i;

	if (rank > si->n_ranks) {
		if (rank > MAX_RANKS) {
			printf("Rank '%d' should not exceed " STRINGIFY(MAX_RANKS), rank);
			rank = MAX_RANKS;
		}
		list = merge_lists(sweep_up(si, NULL, si->n_ranks), list, THUNK_ARG(si->thunk) si->func);
		for (i = si->n_ranks; i < rank; ++i) {
			si->ranks[i] = NULL;
		}
	}
	else {
		if (rank) {
			list = merge_lists(sweep_up(si, NULL, rank), list, THUNK_ARG(si->thunk) si->func);
		}
		for (i = rank; i < si->n_ranks && si->ranks[i]; ++i) {
			list = merge_lists(si->ranks[i], list, THUNK_ARG(si->thunk) si->func);
			si->ranks[i] = NULL;
		}
	}

	/* Will _never_ happen: so we can just devolve into quadratic ;-) */
	if (i == MAX_RANKS) {
		i--;
	}

	if (i >= si->n_ranks) {
		si->n_ranks = i + 1;
	}

	si->min_rank = i;
	si->ranks[i] = list;
}

#undef MAX_RANKS
#undef FLOOR_LOG2

/* A non-recursive mergesort */
static inline digit list_sort_do(
        list_node *list,
        CompareFn func
#ifdef SORT_IMPL_USE_THUNK
        , void *thunk
#endif
        )
{
	struct SortInfo si;

	init_sort_info(
	        &si,
	        func
#ifdef SORT_IMPL_USE_THUNK
	        , thunk
#endif
	        );

	while (list && list->next) {
		list_node *next = list->next;
		list_node *tail = next->next;

		if (func(THUNK_ARG(thunk) SORT_ARG(list), SORT_ARG(next)) > 0) {
			next->next = list;
			next = list;
			list = list->next;
		}
		next->next = NULL;

		insert_list(&si, list, 0);

		list = tail;
	}

	return sweep_up(&si, list, si.n_ranks);
}

#undef _CONCAT_AUX
#undef _CONCAT
#undef _SORT_PREFIX

#undef SortInfo
#undef CompareFn
#undef init_sort_info
#undef merge_lists
#undef sweep_up
#undef insert_list
#undef digit

#undef list_node
#undef list_sort_do

#undef THUNK_ARG
#undef SORT_ARG