added 16-bit hashing

include/pearson.h

@@ -19,3 +19,5 @@
 void pearson_hash_256 (uint8_t *out, const uint8_t *in, size_t len);
 
 void pearson_hash_128 (uint8_t *out, const uint8_t *in, size_t len);
+
+uint16_t pearson_hash_16 (const uint8_t *in, size_t len);

src/pearson.c

@@ -219,3 +219,23 @@ void pearson_hash_128 (uint8_t *out, const uint8_t *in, size_t len) {
   o = (uint64_t*)&out[8];
   *o = lower_hash;
 }
+
+
+// 16-bit hash: the return value has to be interpreted as uint16_t and
+// follows machine-specific endianess in memory
+uint16_t pearson_hash_16 (const uint8_t *in, size_t len) {
+
+	uint16_t hash = 0;
+        uint16_t hash_mask = 0x0100;
+
+        for (size_t i = 0; i < len; i++) {
+                // broadcast the character, xor into hash, make them different permutations
+                uint16_t c = (uint8_t)in[i];
+                c |= c <<  8;
+                hash ^= c ^ hash_mask;
+                // table lookup
+		hash = t[(uint8_t)hash] + (t[hash >> 8] << 8);
+        }
+        // output
+        return hash;
+}