1 files changed, 98 insertions, 0 deletions
diff --git a/lib/csum.c b/lib/csum.c
new file mode 100644
index 00000000..5266be6d
--- /dev/null
+++ b/lib/csum.c
@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2008 Nicira Networks.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <config.h>
+#include "csum.h"
+
+/* Returns the IP checksum of the 'n' bytes in 'data'. */
+uint16_t
+csum(const void *data, size_t n)
+{
+    return csum_finish(csum_continue(0, data, n));
+}
+
+/* Adds the 16 bits in 'new' to the partial IP checksum 'partial' and returns
+ * the updated checksum.  (To start a new checksum, pass 0 for 'partial'.  To
+ * obtain the finished checksum, pass the return value to csum_finish().) */
+uint32_t
+csum_add16(uint32_t partial, uint16_t new)
+{
+    return partial + new;
+}
+
+/* Adds the 32 bits in 'new' to the partial IP checksum 'partial' and returns
+ * the updated checksum.  (To start a new checksum, pass 0 for 'partial'.  To
+ * obtain the finished checksum, pass the return value to csum_finish().) */
+uint32_t
+csum_add32(uint32_t partial, uint32_t new)
+{
+    return partial + (new >> 16) + (new & 0xffff);
+}
+
+
+/* Adds the 'n' bytes in 'data' to the partial IP checksum 'partial' and
+ * returns the updated checksum.  (To start a new checksum, pass 0 for
+ * 'partial'.  To obtain the finished checksum, pass the return value to
+ * csum_finish().) */
+uint32_t
+csum_continue(uint32_t partial, const void *data_, size_t n)
+{
+    const uint16_t *data = data_;
+
+    for (; n > 1; n -= 2) {
+        partial = csum_add16(partial, *data++);
+    }
+    if (n) {
+        partial += *(uint8_t *) data;
+    }
+    return partial;
+}
+
+/* Returns the IP checksum corresponding to 'partial', which is a value updated
+ * by some combination of csum_add16(), csum_add32(), and csum_continue(). */
+uint16_t
+csum_finish(uint32_t partial)
+{
+    return ~((partial & 0xffff) + (partial >> 16));
+}
+
+/* Returns the new checksum for a packet in which the checksum field previously
+ * contained 'old_csum' and in which a field that contained 'old_u16' was
+ * changed to contain 'new_u16'. */
+uint16_t
+recalc_csum16(uint16_t old_csum, uint16_t old_u16, uint16_t new_u16)
+{
+    /* Ones-complement arithmetic is endian-independent, so this code does not
+     * use htons() or ntohs().
+     *
+     * See RFC 1624 for formula and explanation. */
+    uint16_t hc_complement = ~old_csum;
+    uint16_t m_complement = ~old_u16;
+    uint16_t m_prime = new_u16;
+    uint32_t sum = hc_complement + m_complement + m_prime;
+    uint16_t hc_prime_complement = sum + (sum >> 16);
+    return ~hc_prime_complement;
+}
+
+/* Returns the new checksum for a packet in which the checksum field previously
+ * contained 'old_csum' and in which a field that contained 'old_u32' was
+ * changed to contain 'new_u32'. */
+uint16_t
+recalc_csum32(uint16_t old_csum, uint32_t old_u32, uint32_t new_u32)
+{
+    return recalc_csum16(recalc_csum16(old_csum, old_u32, new_u32),
+                         old_u32 >> 16, new_u32 >> 16);
+}