From ab35e5fac02f11f0bd742020b112a09e5b1f2de5 Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex.auvolat@ens.fr>
Date: Tue, 16 Dec 2014 21:21:46 +0100
Subject: Add simple hash table implementation.

---
 kernel/lib/hashtbl.c | 166 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 166 insertions(+)
 create mode 100644 kernel/lib/hashtbl.c

(limited to 'kernel/lib/hashtbl.c')

diff --git a/kernel/lib/hashtbl.c b/kernel/lib/hashtbl.c
new file mode 100644
index 0000000..91fb3cb
--- /dev/null
+++ b/kernel/lib/hashtbl.c
@@ -0,0 +1,166 @@
+#include <hashtbl.h>
+#include <kmalloc.h>
+#include <string.h>
+
+#define DEFAULT_INIT_SIZE 16
+#define SLOT_OF_HASH(k, nslots) (((size_t)(k)*21179)%(size_t)(nslots))
+
+typedef struct hashtbl_item {
+	void* key;
+	void* val;
+	struct hashtbl_item *next;
+} hashtbl_item_t;
+
+// When nitems > size * 3/4, size is multiplied by two
+// When nitems < size * 1/4, size is divided by two
+struct hashtbl {
+	key_eq_fun_t ef;
+	hash_fun_t hf;
+	size_t size, nitems;
+	hashtbl_item_t **items;
+};
+
+hashtbl_t *create_hashtbl(key_eq_fun_t ef, hash_fun_t hf, size_t initial_size) {
+	hashtbl_t *ht = (hashtbl_t*)kmalloc(sizeof(hashtbl_t));
+	if (ht == 0) return 0;
+
+	ht->ef = ef;
+	ht->hf = hf;
+
+	ht->size = (initial_size == 0 ? DEFAULT_INIT_SIZE : initial_size);
+	ht->nitems = 0;
+
+	ht->items = (hashtbl_item_t**)kmalloc(ht->size * sizeof(hashtbl_item_t*));
+	if (ht->items == 0) {
+		kfree(ht);
+		return 0;
+	}
+
+	for (size_t i = 0; i < ht->size; i++) ht->items[i] = 0;
+
+	return ht;
+}
+
+void delete_hashtbl(hashtbl_t *ht) {
+	// Free items
+	for (size_t i = 0; i < ht->size; i++) {
+		while (ht->items[i] != 0) {
+			hashtbl_item_t *n = ht->items[i]->next;
+			kfree(ht->items[i]);
+			ht->items[i] = n;
+		}
+	}
+
+	// Free table
+	kfree(ht->items);
+	kfree(ht);
+}
+
+static void hashtbl_check_size(hashtbl_t *ht) {
+	size_t nsize = 0;
+	if (4 * ht->nitems < ht->size) nsize = ht->size / 2;
+	if (4 * ht->nitems > 3 * ht->size) nsize = ht->size * 2;
+
+	if (nsize != 0) {
+		hashtbl_item_t **nitems = (hashtbl_item_t**)kmalloc(nsize * sizeof(hashtbl_item_t*));
+		if (nitems == 0) return;	// if we can't realloc, too bad, we just lose space
+
+		for (size_t i = 0; i < nsize; i++) nitems[i] = 0;
+
+		// rehash
+		for (size_t i = 0; i < ht->size; i++) {
+			while (ht->items[i] != 0) {
+				hashtbl_item_t *x = ht->items[i];
+				ht->items[i] = x->next;
+
+				size_t slot = SLOT_OF_HASH(ht->hf(x->key), nsize);
+				x->next = nitems[slot];
+				nitems[slot] = x;
+			}
+		}
+		kfree(ht->items);
+		ht->size = nsize;
+		ht->items = nitems;
+	}
+}
+
+int hashtbl_add(hashtbl_t *ht, void* key, void* v) {
+	size_t slot = SLOT_OF_HASH(ht->hf(key), ht->size);
+
+	hashtbl_item_t *i = (hashtbl_item_t*)kmalloc(sizeof(hashtbl_item_t));
+	if (i == 0) return 1;	// OOM
+
+	// make sure item is not already present
+	hashtbl_remove(ht, key);
+
+	i->key = key;
+	i->val = v;
+	i->next = ht->items[slot];
+	ht->items[slot] = i;
+	ht->nitems++;
+
+	hashtbl_check_size(ht);
+
+	return 0;
+}
+
+void* hashtbl_find(hashtbl_t* ht, void* key) {
+	size_t slot = SLOT_OF_HASH(ht->hf(key), ht->size);
+
+	for (hashtbl_item_t *i = ht->items[slot]; i != 0; i = i->next) {
+		if (ht->ef(i->key, key)) return i->val;
+	}
+
+	return 0;
+}
+
+void hashtbl_remove(hashtbl_t* ht, void* key) {
+	size_t slot = SLOT_OF_HASH(ht->hf(key), ht->size);
+
+	if (ht->items[slot] == 0) return;
+
+	if (ht->ef(ht->items[slot]->key, key)) {
+		hashtbl_item_t *x = ht->items[slot];
+		ht->items[slot] = x->next;
+		kfree(x);
+		ht->nitems--;
+	} else {
+		for (hashtbl_item_t *i = ht->items[slot]; i->next != 0; i = i->next) {
+			if (ht->ef(i->next->key, key)) {
+				hashtbl_item_t *x = i->next;
+				i->next = x->next;
+				kfree(x);
+				ht->nitems--;
+				break;
+			}
+		}
+	}
+	
+	hashtbl_check_size(ht);
+}
+
+size_t hashtbl_count(hashtbl_t* ht) {
+	return ht->nitems;
+}
+
+hash_t id_hash_fun(const void* v) {
+	return (hash_t)v;
+}
+
+hash_t str_hash_fun(const void* v) {
+	hash_t h = 712;
+	for (char* s = (char*)v; *s != 0; s++) {
+		h = h * 101 + *s;
+	}
+	return h;
+}
+
+bool id_key_eq_fun(const void* a, const void* b) {
+	return a == b;
+}
+
+bool str_key_eq_fun(const void* a, const void* b) {
+	return strcmp((const char*)a, (const char*)b) == 0;
+}
+
+/* vim: set ts=4 sw=4 tw=0 noet :*/
-- 
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