3 files changed, 66 insertions, 0 deletions
diff --git a/src/commonlib/Makefile.mk b/src/commonlib/Makefile.mk
index 70e731df35..7ec4de91c0 100644
--- a/src/commonlib/Makefile.mk
+++ b/src/commonlib/Makefile.mk
@@ -61,3 +61,5 @@ smm-y += bsd/elog.c
 
 decompressor-y += bsd/gcd.c
 all-y += bsd/gcd.c
+
+all-y += bsd/ipchksum.c
diff --git a/src/commonlib/bsd/include/commonlib/bsd/ipchksum.h b/src/commonlib/bsd/include/commonlib/bsd/ipchksum.h
new file mode 100644
index 0000000000..91d6872d9f
--- /dev/null
+++ b/src/commonlib/bsd/include/commonlib/bsd/ipchksum.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: BSD-3-Clause */
+
+#ifndef _COMMONLIB_BSD_IPCHKSUM_H_
+#define _COMMONLIB_BSD_IPCHKSUM_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+uint16_t ipchksum(const void *data, size_t size);
+uint16_t ipchksum_add(size_t offset, uint16_t first, uint16_t second);
+
+#endif /* _COMMONLIB_BSD_IPCHKSUM_H_ */
diff --git a/src/commonlib/bsd/ipchksum.c b/src/commonlib/bsd/ipchksum.c
new file mode 100644
index 0000000000..a40b86cbb4
--- /dev/null
+++ b/src/commonlib/bsd/ipchksum.c
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0-or-later */
+
+#include <commonlib/bsd/ipchksum.h>
+
+/* See RFC 1071 for mathematical explanations of why we can first sum in a larger register and
+   then narrow down, why we don't need to worry about endianness, etc. */
+uint16_t ipchksum(const void *data, size_t size)
+{
+	const uint8_t *p1 = data;
+	unsigned long wide_sum = 0;
+	uint32_t sum = 0;
+	size_t i = 0;
+
+	while (wide_sum) {
+		sum += wide_sum & 0xFFFF;
+		wide_sum >>= 16;
+	}
+	sum = (sum & 0xFFFF) + (sum >> 16);
+
+	for (; i < size; i++) {
+		uint32_t v = p1[i];
+		if (i % 2)
+			v <<= 8;
+		sum += v;
+
+		/* Doing this unconditionally seems to be faster. */
+		sum = (sum & 0xFFFF) + (sum >> 16);
+	}
+
+	return (uint16_t)~sum;
+}
+
+uint16_t ipchksum_add(size_t offset, uint16_t first, uint16_t second)
+{
+	first = ~first;
+	second = ~second;
+
+	/*
+	 * Since the checksum is calculated in 16-bit chunks, if the offset at which
+	 * the data covered by the second checksum would start (if both data streams
+	 * came one after the other) is odd, that means the second stream starts in
+	 * the middle of a 16-bit chunk. This means the second checksum is byte
+	 * swapped compared to what we need it to be, and we must swap it back.
+	 */
+	if (offset % 2)
+		second = (second >> 8) | (second << 8);
+
+	uint32_t sum = first + second;
+	sum = (sum & 0xFFFF) + (sum >> 16);
+
+	return (uint16_t)~sum;
+}