Add hash map routines

2023-11-12 13:53:08 -05:00
parent fd98d65ef6
commit edea2a350d
4 changed files with 202 additions and 11 deletions
--- a/libXmd/src/Map.c
+++ b/libXmd/src/Map.c
@@ -0,0 +1,161 @@
+#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);
+			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;
+}