xdp-project-bpf-examples/AF_XDP-interaction/lib_checksum.h

// SPDX-License-Identifier: GPL-2.0
// Code taken from kernel samples/bpf/xdpsock_user.c

#ifndef __LIB_CHECKSUM_H
#define __LIB_CHECKSUM_H

static void *memset32_htonl(void *dest, __u32 val, __u32 size)
{
	__u32 *ptr = (__u32 *)dest;
	int i;

	val = htonl(val);

	for (i = 0; i < (size & (~0x3)); i += 4)
		ptr[i >> 2] = val;

	for (; i < size; i++)
		((char *)dest)[i] = ((char *)&val)[i & 3];

	return dest;
}

/*
 * This function code has been taken from
 * Linux kernel lib/checksum.c
 */
static inline unsigned short from32to16(unsigned int x)
{
	/* add up 16-bit and 16-bit for 16+c bit */
	x = (x & 0xffff) + (x >> 16);
	/* add up carry.. */
	x = (x & 0xffff) + (x >> 16);
	return x;
}

/*
 * This function code has been taken from
 * Linux kernel lib/checksum.c
 */
static unsigned int do_csum(const unsigned char *buff, int len)
{
	unsigned int result = 0;
	int odd;

	if (len <= 0)
		goto out;
	odd = 1 & (unsigned long)buff;
	if (odd) {
#ifdef __LITTLE_ENDIAN
		result += (*buff << 8);
#else
		result = *buff;
#endif
		len--;
		buff++;
	}
	if (len >= 2) {
		if (2 & (unsigned long)buff) {
			result += *(unsigned short *)buff;
			len -= 2;
			buff += 2;
		}
		if (len >= 4) {
			const unsigned char *end = buff +
						   ((unsigned int)len & ~3);
			unsigned int carry = 0;

			do {
				unsigned int w = *(unsigned int *)buff;

				buff += 4;
				result += carry;
				result += w;
				carry = (w > result);
			} while (buff < end);
			result += carry;
			result = (result & 0xffff) + (result >> 16);
		}
		if (len & 2) {
			result += *(unsigned short *)buff;
			buff += 2;
		}
	}
	if (len & 1)
#ifdef __LITTLE_ENDIAN
		result += *buff;
#else
		result += (*buff << 8);
#endif
	result = from32to16(result);
	if (odd)
		result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
out:
	return result;
}

/*
 *	This is a version of ip_compute_csum() optimized for IP headers,
 *	which always checksum on 4 octet boundaries.
 *	This function code has been taken from
 *	Linux kernel lib/checksum.c
 */
static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
{
	return (__sum16)~do_csum(iph, ihl * 4);
}

/*
 * Fold a partial checksum
 * This function code has been taken from
 * Linux kernel include/asm-generic/checksum.h
 */
static inline __sum16 csum_fold(__wsum csum)
{
	__u32 sum = (__u32)csum;

	sum = (sum & 0xffff) + (sum >> 16);
	sum = (sum & 0xffff) + (sum >> 16);
	return (__sum16)~sum;
}

/*
 * This function code has been taken from
 * Linux kernel lib/checksum.c
 */
static inline __u32 from64to32(__u64 x)
{
	/* add up 32-bit and 32-bit for 32+c bit */
	x = (x & 0xffffffff) + (x >> 32);
	/* add up carry.. */
	x = (x & 0xffffffff) + (x >> 32);
	return (__u32)x;
}

__wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
			  __u32 len, __u8 proto, __wsum sum);

/*
 * This function code has been taken from
 * Linux kernel lib/checksum.c
 */
__wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
			  __u32 len, __u8 proto, __wsum sum)
{
	unsigned long long s = (__u32)sum;

	s += (__u32)saddr;
	s += (__u32)daddr;
#ifdef __BIG_ENDIAN__
	s += proto + len;
#else
	s += (proto + len) << 8;
#endif
	return (__wsum)from64to32(s);
}

/*
 * This function has been taken from
 * Linux kernel include/asm-generic/checksum.h
 */
static inline __sum16
csum_tcpudp_magic(__be32 saddr, __be32 daddr, __u32 len,
		  __u8 proto, __wsum sum)
{
	return csum_fold(csum_tcpudp_nofold(saddr, daddr, len, proto, sum));
}

static inline __u16 udp_csum(__u32 saddr, __u32 daddr, __u32 len,
			   __u8 proto, __u16 *udp_pkt)
{
	__u32 csum = 0;
	__u32 cnt = 0;

	/* udp hdr and data */
	for (; cnt < len; cnt += 2)
		csum += udp_pkt[cnt >> 1];

	return csum_tcpudp_magic(saddr, daddr, len, proto, csum);
}

#endif /* __LIB_CHECKSUM_H */