diff --git a/fs.cpp b/fs_old.cpp
similarity index 100%
rename from fs.cpp
rename to fs_old.cpp
diff --git a/hashtable.c b/hashtable.c
new file mode 100644
index 0000000..2eb87b5
--- /dev/null
+++ b/hashtable.c
@@ -0,0 +1,177 @@
+/*
+ * hashtable.c
+ *
+ *  Created on: 24.10.2017
+ *      Author: julian
+ */
+
+#include "strhash.h"
+#include "hashtable.h"
+
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <errno.h>
+#include <assert.h>
+
+int key_compare(entry_key_t one, entry_key_t two) {
+	return strcmp(one, two) == 0;
+}
+
+entry_hash_t key_hash(entry_key_t key) {
+	return hash_str(key) + 1; // make hash always nonzero
+}
+
+hashtable_iterator_t hashtable_end(struct hashtable * table) {
+	return table->data + table->len;
+}
+
+
+hashtable_iterator_t hashtable_next(struct hashtable * table, hashtable_iterator_t current) {
+	if (table == NULL) {
+		return NULL;
+	}
+
+	if (current == NULL) {
+		current = table->data;
+	} else {
+		// we want the NEXT pointer :)
+		current++;
+	}
+
+	while(current != hashtable_end(table)) {
+		if (current->hash != 0)
+			break;
+
+		current++;
+	}
+
+	return current;
+}
+
+hashtable_iterator_t hashtable_get_hash(struct hashtable * table, entry_hash_t hash) {
+	size_t index = hash % table->len;
+
+	if (table->data[index].hash == 0) {
+		return hashtable_end(table);
+	}
+
+	return table->data + index;
+}
+
+hashtable_iterator_t hashtable_get(struct hashtable * table, entry_key_t key) {
+	entry_hash_t hash = key_hash(key);
+	return hashtable_get_hash(table, hash);
+}
+
+void hashtable_clear(struct hashtable * table) {
+	if (table->dealloc_data) {
+		hashtable_iterator_t it = hashtable_next(table, NULL);
+		for(;it != hashtable_end(table); it = hashtable_next(table, it)){
+			table->dealloc_data(it->data);
+		}
+	}
+
+	free(table->data);
+	table->data = NULL;
+	table->count = table->len = 0;
+}
+
+int hashtable_resize(struct hashtable * table, size_t newsize) {
+	if (table == NULL) {
+		return 0;
+	}
+
+	if (newsize == 0) {
+		// will fail, correct to 1
+		newsize = 1;
+	}
+
+	struct hashtable temp = *table;
+	table->data = calloc(newsize, sizeof(struct entry));
+
+	if (table->data == NULL) {
+		table->data = temp.data;
+
+		errno = ENOMEM;
+		return -1;
+	}
+
+	// try to reinsert old data
+	table->len = newsize;
+
+	for (size_t i = 0; i < temp.len; i++) {
+		if (temp.data[i].hash && hashtable_add(table, temp.data[i]) == -1) {
+			// abort mission, restore old table
+			free(table->data);
+			*table = temp;
+
+			return -2;
+		}
+	}
+
+	// delete old table
+	free(temp.data);
+
+	return 0;
+}
+
+int hashtable_add(struct hashtable * table, struct entry entry) {
+	if (table == NULL) {
+		return 0;
+	}
+
+	if (table->len == 0) {
+		// initial alloc
+		int err = hashtable_resize(table, 1);
+
+		if (err < 0) {
+			return err;
+		}
+		return hashtable_add(table, entry);
+	}
+
+
+	// try to insert into table
+	size_t index = entry.hash % table->len;
+
+	if (table->data->hash && !key_compare(table->data[index].key, entry.key)) {
+		// key collision
+		// make table bigger
+		if (hashtable_resize(table, table->len*2) != 0) {
+			return -1;
+		}
+
+		return hashtable_add(table, entry);
+	}
+
+	// insert new entry
+	table->data[index] = entry;
+	table->count++;
+	return 0;
+}
+
+struct entry hashtable_make_entry(entry_key_t key, void * data) {
+	return (struct entry){ .data = data,
+		.key = key,
+		.hash = key_hash(key),
+	};
+}
+
+int hashtable_remove(struct hashtable * table, hashtable_iterator_t it) {
+	if (!it || it->hash == 0) {
+		return 0;
+	}
+
+	if (table->dealloc_data) {
+		table->dealloc_data(it->data);
+	}
+
+	it->data = NULL;
+	it->hash = 0;
+	table->count--;
+	return 1;
+}
+
+
diff --git a/hashtable.h b/hashtable.h
new file mode 100644
index 0000000..b354521
--- /dev/null
+++ b/hashtable.h
@@ -0,0 +1,117 @@
+/*
+ * hashtable.h
+ *
+ *  Created on: 21.10.2017
+ *      Author: julian
+ */
+
+#ifndef HASHTABLE_H_
+#define HASHTABLE_H_
+
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+#include "strhash.h"
+#include <errno.h>
+#include <assert.h>
+
+
+typedef strhash_t entry_hash_t;
+typedef const char * entry_key_t;
+typedef struct entry * hashtable_iterator_t;
+
+// data deallocator
+typedef void(*hashtable_dealloc)(void*);
+// data copy and allocator
+typedef void(*hashtable_alloc)(void*);
+
+extern int key_compare(entry_key_t one, entry_key_t two);
+extern entry_hash_t key_hash(entry_key_t key);
+
+struct entry {
+	entry_hash_t hash;
+	entry_key_t key;
+	void * data;
+};
+
+struct hashtable {
+	struct entry * data;
+	size_t len, count;
+
+	hashtable_alloc alloc_data;
+	hashtable_dealloc dealloc_data;
+};
+
+extern hashtable_iterator_t hashtable_end(struct hashtable * table);
+
+/**
+ * Iterate of the hashmap.
+ *
+ * pass the return value to current to iterate over the entire map
+ * pass NULL to get the beginning
+ *
+ * returns the next set entry in the table from current
+ * returns hashtable_end() when there is nons
+ * example loop:
+ * hashmap_iterator_t current = hashtable_next(table, NULL);
+ * for(;current != hashtable_end(table); current = hashtable_next(table, current)) {}
+ *
+ */
+hashtable_iterator_t hashtable_next(struct hashtable * table, hashtable_iterator_t current);
+
+/**
+ * returns the entry identified by the given hash
+ * returns hashtable_end() if no entry matched
+ */
+hashtable_iterator_t hashtable_get_hash(struct hashtable * table, entry_hash_t hash);
+
+/**
+ * returns the entry identified by the given key
+ * returns hashtable_end() if no entry matched
+ */
+hashtable_iterator_t hashtable_get(struct hashtable * table, entry_key_t key);
+
+/**
+ * delete all entries of the given table
+ *
+ * calls dealloc of the table for every data element, if it was set.
+ */
+void hashtable_clear(struct hashtable * table);
+
+/**
+ * insert a new element in the table
+ */
+int hashtable_add(struct hashtable * table, struct entry entry);
+
+/**
+ * resize the hashtable to a new physical size
+ * can also try to make the hashtable smaller
+ *
+ * returns 0 on success
+ * returns -1 on error (sets errno)
+ * returns -2 if hashtable does not fit in new size.
+ */
+int hashtable_resize(struct hashtable * table, size_t newsize);
+
+/**
+ * add new element in hashtable
+ *
+ * returns 0 on success
+ * returns -1 on error
+ */
+int hashtable_add(struct hashtable * table, struct entry entry);
+
+/**
+ * make a new entry that can be added out of key and data
+ */
+struct entry hashtable_make_entry(entry_key_t key, void * data);
+
+/**
+ * remove one entry using the key
+ * @return -1 on error
+ * @return 1 on success
+ * @return 0 on not found
+ */
+int hashtable_remove(struct hashtable * table, hashtable_iterator_t it);
+
+#endif /* HASHTABLE_H_ */
diff --git a/main.cpp b/main_old.cpp
similarity index 100%
rename from main.cpp
rename to main_old.cpp
diff --git a/strhash.c b/strhash.c
new file mode 100644
index 0000000..53f338d
--- /dev/null
+++ b/strhash.c
@@ -0,0 +1,28 @@
+/*
+ * strhash.c
+ *
+ *  Created on: 21.10.2017
+ *      Author: julian
+ */
+
+#include "strhash.h"
+
+// use rule:
+// hash(i) = hash(i - 1) * 33 ^ str[i]
+// see: http://www.cse.yorku.ca/~oz/hash.html
+strhash_t hash_add(strhash_t hash, char  c) {
+	return hash * 33 ^ c;
+}
+
+
+strhash_t hash_str(const char * str) {
+	strhash_t hash = 0;
+	while(*str) {
+		hash = hash_add(hash, *str);
+		str++;
+	}
+
+	return hash;
+}
+
+
diff --git a/strhash.h b/strhash.h
new file mode 100644
index 0000000..7c67f78
--- /dev/null
+++ b/strhash.h
@@ -0,0 +1,23 @@
+/*
+ * strhash.h
+ *
+ *  Created on: 21.10.2017
+ *      Author: julian
+ */
+
+#ifndef STRHASH_H_
+#define STRHASH_H_
+
+#include <stddef.h>
+
+typedef size_t strhash_t;
+
+// "rehash" string with new char added to end
+strhash_t hash_add(strhash_t hash, char c);
+
+/// hash a given string
+strhash_t hash_str(const char * str);
+
+
+
+#endif /* STRHASH_H_ */
diff --git a/test_hashtable.c b/test_hashtable.c
new file mode 100644
index 0000000..bc4c351
--- /dev/null
+++ b/test_hashtable.c
@@ -0,0 +1,137 @@
+/*
+ * test_hashtable.c
+ *
+ *  Created on: 21.10.2017
+ *      Author: julian
+ */
+
+#include "tests.h"
+#include "hashtable.h"
+
+struct hashtable table = {};
+struct entry nEntry;
+
+
+void testresize() {
+	init("resize");
+	int err = hashtable_resize(&table, 20);
+	if (err != 0) {
+		fail("resize return code was error %d", err);
+	}
+	if (table.len != 20) {
+		fail("table has wrong size %d", table.len);
+	}
+
+	pass();
+}
+
+void testadd() {
+	init("add");
+	nEntry = hashtable_make_entry("hi", "20");
+	size_t count = table.count;
+
+	int err = hashtable_add(&table, nEntry);
+
+	if (err != 0) {
+		fail("add gave error %d", err);
+	}
+	if (table.count != count +1) {
+		fail("table has wrong count (has %d, needs %d)", table.count, count+1);
+	}
+
+	pass();
+}
+
+void testget()  {
+	init("get");
+
+	hashtable_iterator_t elem = hashtable_get(&table, "hi");
+
+	if (elem == hashtable_end(&table)) {
+		fail("element was not found");
+	}
+
+	if (elem->data != nEntry.data) {
+		fail("returned wrong element");
+	}
+
+	pass();
+}
+
+void testiterate() {
+	init("iterate");
+
+	hashtable_iterator_t it = hashtable_next(&table, NULL);
+
+	if (it == hashtable_end(&table)) {
+		fail("table seems empty?");
+	}
+
+	if (strcmp(it->key, "hi")) {
+		fail("wrong entry (smh)");
+	}
+
+
+	pass();
+}
+
+
+volatile int dealloc_called = 0;
+
+void test_dealloc(void* data) {
+	dealloc_called++;
+}
+
+void testremove() {
+	init("remove");
+	dealloc_called = 0;
+	table.dealloc_data = test_dealloc;
+
+	if (hashtable_add(&table, hashtable_make_entry("woop", NULL)) < 0) {
+		fail("could not add");
+	}
+
+	hashtable_iterator_t it = hashtable_get(&table, "woop");
+	int ret = hashtable_remove(&table, it);
+
+	if (ret < 0) {
+		fail("negative return code");
+	}
+	if (!ret) {
+		fail("could not remove");
+	}
+	if (!dealloc_called) {
+		fail("deallocator not called");
+	}
+
+	pass();
+}
+void testclear() {
+	init("clear");
+
+	size_t count = table.count;
+	table.dealloc_data = test_dealloc;
+
+	hashtable_clear(&table);
+	if (table.count != 0 || table.len != 0 || table.data != NULL) {
+		fail("memory was not freed");
+	}
+
+	if (dealloc_called != count) {
+		fail("dealloc was not called for all the data");
+	}
+
+	pass();
+}
+
+int main() {
+	init("hashtable");
+	testresize();
+	testadd();
+	testget();
+	testiterate();
+	testclear();
+	pass();
+}
+
+