AP_Math: add method for generating hash

libraries/AP_Math/crc.cpp

@@ -255,3 +255,14 @@ uint16_t calc_crc_modbus(uint8_t *buf, uint16_t len)
     }
     return crc;
 }
+
+// FNV-1a implementation
+#define FNV_1_PRIME_64 1099511628211UL
+void hash_fnv_1a(uint32_t len, const uint8_t* buf, uint64_t* hash)
+{
+    uint32_t i;
+    for (i=0; i<len; i++) {
+        *hash ^= (uint64_t)buf[i];
+        *hash *= FNV_1_PRIME_64;
+    }
+}

libraries/AP_Math/crc.h

@@ -29,3 +29,7 @@ uint16_t crc16_ccitt(const uint8_t *buf, uint32_t len, uint16_t crc);
 
 uint16_t calc_crc_modbus(uint8_t *buf, uint16_t len);
 
+// generate 64bit FNV1a hash from buffer
+#define FNV_1_OFFSET_BASIS_64 14695981039346656037UL
+void hash_fnv_1a(uint32_t len, const uint8_t* buf, uint64_t* hash);
+