From 97696c7b36dd33a7848558900691e8062b68bc40 Mon Sep 17 00:00:00 2001
From: "7u83@mail.ru" <7u83@mail.ru@noemail.net>
Date: Sun, 24 Aug 2014 18:50:33 +0000
Subject: [PATCH] Checksum for image data message elements.

FossilOrigin-Name: bfe6cf9ca48592aa3fc6f572620b48ed29ba6f383e3ef52bd913758cc9675f35
---
 src/capwap/lw_checksum.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 src/capwap/lw_checksum.c

diff --git a/src/capwap/lw_checksum.c b/src/capwap/lw_checksum.c
new file mode 100644
index 00000000..7c6daf40
--- /dev/null
+++ b/src/capwap/lw_checksum.c
@@ -0,0 +1,40 @@
+/*
+    This file is part of libcapwap.
+
+    libcapwap is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    libcapwap is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+
+#include "lwapp.h"
+
+/**
+ * Calculate the 16-bit checksum for LWAPP image data  message 
+ * elements with opcode 3 - used by Cisco also in CAPWAP
+ */
+uint16_t lw_checksum(uint8_t * d, int len)
+{
+	int i;
+	uint32_t cs = 0;
+	for (i = 0; i < len; i += 2) {
+		uint16_t w = d[i] << 8;
+
+		if (i + 1 < len)
+			w |= d[i + 1];
+
+		cs += w ^= 0xffff;
+		cs += cs >> 16;
+		cs &= 0xffff;
+	}
+	return (uint16_t) cs;
+}