split djb2 code from hash.c to independent program

hash/hash_djb2.c

@@ -0,0 +1,49 @@
+/**
+ * @addtogroup hash Hash algorithms
+ * @{
+ * @file hash_djb2.c
+ * @author [Christian Bender](https://github.com/christianbender)
+ * @brief [DJB2 hash algorithm](http://www.cse.yorku.ca/~oz/hash.html)
+ */
+#include <assert.h>
+#include <inttypes.h>
+#include <stdio.h>
+
+/**
+ * @brief DJB2 algorithm implementation
+ *
+ * @param s NULL terminated string to hash
+ * @return 64-bit hash result
+ */
+uint64_t djb2(const char* s)
+{
+    uint64_t hash = 5381; /* init value */
+    size_t i = 0;
+    while (s[i] != '\0')
+    {
+        hash = ((hash << 5) + hash) + s[i];
+        i++;
+    }
+    return hash;
+}
+
+/**
+ * @brief Test function for ::sdbm
+ */
+void test_djb2()
+{
+    assert(djb2("Hello World") == 13827776004929097857);
+    assert(djb2("Hello World!") == 13594750393630990530);
+    assert(djb2("Hello world") == 13827776004967047329);
+    assert(djb2("Hello world!") == 13594750394883323106);
+    printf("Tests passed\n");
+}
+
+/** @} */
+
+/** Main function */
+int main()
+{
+    test_djb2();
+    return 0;
+}