til_jenkins: add a rudimentary hash function

Presently just for hashing paths and names

1 files changed, 26 insertions, 0 deletions

diff --git a/src/til_jenkins.c b/src/til_jenkins.c
new file mode 100644
index 0000000..0bc74ba
--- /dev/null
+++ b/src/til_jenkins.c
@@ -0,0 +1,26 @@
+#include <stddef.h>
+#include <stdint.h>
+
+#include "til_jenkins.h"
+
+/* we just need something to hash paths/names, it's not super perf sensitive since
+ * the hashes will be cached @ path/name intialization (they don't change).
+ */
+
+/* simple "one at a time" variant from https://en.wikipedia.org/wiki/Jenkins_hash_function */
+uint32_t til_jenkins(const uint8_t *key, size_t length)
+{
+	uint32_t hash = 0;
+
+	for (size_t i = 0; i < length; i++) {
+		hash += key[i];
+		hash += hash << 10;
+		hash ^= hash >> 6;
+	}
+
+	hash += hash << 3;
+	hash ^= hash >> 11;
+	hash += hash << 15;
+
+	return hash;
+}