Xmd/libXmd/src/Map.c

#include <Xmd/Map.h>
#include <X11/Intrinsic.h>

#define XmdMAP_GROWTH_FACTOR    2
#define XmdMAP_INITIAL_CAPACITY 16

typedef struct _XmdMapElement {
	XmdMapKey              key;
	void                  *value;
	struct _XmdMapElement *sister;
} XmdMapElement;

struct _XmdMap {
	Cardinal      length;
	Cardinal      capacity;
	XmdMapElement **data;
};

static void     XmdMapResizeIfNeeded (XmdMap *map);
static Cardinal XmdMapHash           (XmdMap *map, XmdMapKey key);

XmdMap *XmdMapNew () {
	XmdMap *map = XtNew(XmdMap);
	if (map == NULL) goto fail;
	
	map->length   = 0;
	map->capacity = XmdMAP_INITIAL_CAPACITY;
	map->data = (XmdMapElement **) (
		XtCalloc(map->capacity, sizeof(XmdMapElement *)));
	if (map->data == NULL) goto fail;
	
	return map;
	
	fail:
	XmdMapFree(map);
	return NULL;
}

void *XmdMapGet (XmdMap *map, XmdMapKey key) {
	XmdMapElement *element = map->data[XmdMapHash(map, key)];
	while (element != NULL) {
		if (element->key == key) return element->value;
		element = element->sister;
	}
	return NULL;
}

void *XmdMapSetInternal (XmdMap *map, XmdMapKey key, void *value) {
	/* find bucket */
	XmdMapElement **destination = &map->data[XmdMapHash(map, key)];
	/* find position in bucket */
	while (*destination != NULL) {
		if ((*destination)->key == key) {
			/* element exists already */
			void *previous = (*destination)->value;
			if (value == NULL) {
				/* if setting to NULL, free old element */
				XmdMapElement *element = *destination;
				*destination = element->sister;
				XtFree((char *)(element));
			} else {
				/* otherwise, replace value */
				(*destination)->value = value;
			}
			return previous;
		}
		destination = &((*destination)->sister);
	}
	/* element does not exist already */
	if (value != NULL) {
		/* allocate new element and append */
		*destination = XtNew(XmdMapElement);
		(*destination)->key    = key;
		(*destination)->value  = value;
		(*destination)->sister = NULL;
	}
	return NULL;
}

void *XmdMapSet (XmdMap *map, XmdMapKey key, void *value) {
	void *previous = XmdMapSetInternal(map, key, value);
	if (value == NULL) {
		if (previous != NULL) map->length --;
	} else {
		if (previous == NULL) map->length ++;
	}
	XmdMapResizeIfNeeded(map);
	return previous;
}

void XmdMapIterate (XmdMap *map, XmdMapIterator iterator) {
	for (Cardinal index = 0; index < map->capacity; index ++) {
		XmdMapElement *element = map->data[index];
		while (element != NULL) {
			if(!iterator(map, element->key, element->value)) break;
			element = element->sister;
		}
	}
}

Cardinal XmdMaplength (XmdMap *map) {
	return map->length;
}

void XmdMapFree (XmdMap *map) {
	if (map == NULL) return;
	XtFree((char *)(map->data));
	XtFree((char *)(map));
}

void XmdMapResizeIfNeeded (XmdMap *map) {
	Cardinal        oldCapacity = map->capacity;
	XmdMapElement **oldData     = map->data;
	
	/* figure out what the new capacity should be. if the map length is
	   very small compared to the map capacity, shrink the map to save
	   memory. if the map length is getting large compared to the map
	   capacity, grow the map to reduce collisions. if the map length is
	   neither too big nor too small, do nothing because rehashing is an
	   expensive operation. */
	if (map->length + XmdMAP_INITIAL_CAPACITY < map->capacity / 4) {
		map->capacity /= XmdMAP_GROWTH_FACTOR;
	} else if (map->length > (map->capacity * 2) / 3) {
		map->capacity *= XmdMAP_GROWTH_FACTOR;
	} else {
		return;
	}
	
	/* rehash */
	map->data = (XmdMapElement **) (
		XtCalloc(map->capacity, sizeof(XmdMapElement)));
	for (Cardinal index = 0; index < oldCapacity; index ++) {
		XmdMapElement *element = oldData[index];
		while (element != NULL) {
			XmdMapSetInternal(map, element->key, element->value);
			XmdMapElement *sister = element->sister;
			XtFree((char *)(element));
			element = sister;
		}
	}
	
	XtFree((char *)(oldData));
}

static Cardinal XmdMapHash (XmdMap *map, XmdMapKey key) {
	/* https://web.archive.org/web/20160329102146/http://elliottback.com/wp/
	   hashmap-implementation-in-c/ */

	/* Robert Jenkins' 32 bit Mix Function */
	key += (key << 12);
	key ^= (key >> 22);
	key += (key << 4);
	key ^= (key >> 9);
	key += (key << 10);
	key ^= (key >> 2);
	key += (key << 7);
	key ^= (key >> 12);

	/* Knuth's Multiplicative Method */
	key = (key >> 3) * 2654435761;

	return key % map->capacity;
}