inet_csum: initial import of Internet Checksum module

sys/Makefile

@@ -71,6 +71,9 @@ endif
 ifneq (,$(filter ng_ipv6_netif,$(USEMODULE)))
     DIRS += net/network_layer/ng_ipv6/netif
 endif
+ifneq (,$(filter ng_inet_csum,$(USEMODULE)))
+    DIRS += net/crosslayer/ng_inet_csum
+endif
 ifneq (,$(filter ng_netapi,$(USEMODULE)))
     DIRS += net/crosslayer/ng_netapi
 endif

sys/include/net/ng_inet_csum.h

@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2015 Martine Lenders <mlenders@inf.fu-berlin.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @defgroup    net_ng_inet_csum    Internet Checksum
+ * @ingroup     net
+ * @brief   Provides a function to calculate the Internet Checksum
+ * @{
+ *
+ * @file
+ * @brief   Internet Checksum definitions
+ *
+ * @author  Martine Lenders <mlenders@inf.fu-berlin.de>
+ */
+#ifndef NG_INET_CSUM_H_
+#define NG_INET_CSUM_H_
+
+#include <inttypes.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief   Calculates the unnormalized Internet Checksum of @p buf.
+ *
+ * @see <a href="https://tools.ietf.org/html/rfc1071">
+ *          RFC 1071
+ *      </a>
+ *
+ * @details The Internet Checksum is not normalized (i. e. its 1's complement
+ *          was not taken of the result) to use it for further calculation.
+ *
+ * @param[in] sum   An initial value for the checksum.
+ * @param[in] buf   A buffer.
+ * @param[in] len   Length of @p buf in byte.
+ *
+ * @return  The unnormalized Internet Checksum of @p buf.
+ */
+uint16_t ng_inet_csum(uint16_t sum, const uint8_t *buf, uint16_t len);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* NG_INET_CSUM_H_ */
+/** @} */

sys/net/crosslayer/ng_inet_csum/Makefile

@@ -0,0 +1 @@
+include $(RIOTBASE)/Makefile.base

sys/net/crosslayer/ng_inet_csum/ng_inet_csum.c

@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2015 Martine Lenders <mlenders@inf.fu-berlin.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @{
+ *
+ * @file
+ */
+
+#include <stdio.h>
+#include "net/ng_inet_csum.h"
+
+uint16_t ng_inet_csum(uint16_t sum, const uint8_t *buf, uint16_t len)
+{
+    uint32_t csum = sum;
+
+    for (int i = 0; i < (len >> 1); buf += 2, i++) {
+        csum += (*buf << 8) + *(buf + 1);   /* group bytes by 16-byte words
+                                             * and add them*/
+    }
+
+    if (len & 1) {                      /* if len is odd */
+        csum += (*buf << 8);            /* add last byte as top half of 16-byte word */
+    }
+
+    csum += csum >> 16;
+
+    return (csum & 0xffff);
+}
+
+/** @} */