From 3c1e99cc6b426db2f3d085c037e4aafad3d60a0a Mon Sep 17 00:00:00 2001
From: Siddharth Purohit <siddharthbharatpurohit@gmail.com>
Date: Sun, 6 Oct 2019 11:06:19 +0530
Subject: [PATCH] AP_Math: add method for generating hash

---
 libraries/AP_Math/AP_Math.cpp |  1 +
 libraries/AP_Math/AP_Math.h   |  1 +
 libraries/AP_Math/crc.cpp     | 11 +++++++++++
 libraries/AP_Math/crc.h       |  4 ++++
 4 files changed, 17 insertions(+)

diff --git a/libraries/AP_Math/AP_Math.cpp b/libraries/AP_Math/AP_Math.cpp
index fc0b341547..d621fc2fe1 100644
--- a/libraries/AP_Math/AP_Math.cpp
+++ b/libraries/AP_Math/AP_Math.cpp
@@ -338,6 +338,7 @@ bool rotation_equal(enum Rotation r1, enum Rotation r2)
     return (v1 - v2).length() < 0.001;
 }
 
+
 #if CONFIG_HAL_BOARD == HAL_BOARD_SITL
 // fill an array of float with NaN, used to invalidate memory in SITL
 void fill_nanf(float *f, uint16_t count)
diff --git a/libraries/AP_Math/AP_Math.h b/libraries/AP_Math/AP_Math.h
index 160d3fbd63..8d7b2c5365 100644
--- a/libraries/AP_Math/AP_Math.h
+++ b/libraries/AP_Math/AP_Math.h
@@ -281,3 +281,4 @@ bool rotation_equal(enum Rotation r1, enum Rotation r2) WARN_IF_UNUSED;
 // fill an array of float with NaN, used to invalidate memory in SITL
 void fill_nanf(float *f, uint16_t count);
 #endif
+
diff --git a/libraries/AP_Math/crc.cpp b/libraries/AP_Math/crc.cpp
index a53540de61..7c5a017c50 100644
--- a/libraries/AP_Math/crc.cpp
+++ b/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;
+    }
+}
diff --git a/libraries/AP_Math/crc.h b/libraries/AP_Math/crc.h
index cd81977785..2a307734ca 100644
--- a/libraries/AP_Math/crc.h
+++ b/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);
+