// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *
 * INET         An implementation of the TCP/IP protocol suite for the LINUX
 *              operating system.  INET is implemented using the  BSD Socket
 *              interface as the means of communication with the user level.
 *
 *              IP/TCP/UDP checksumming routines
 *
 * Authors:     Jorge Cwik, <jorge@laser.satlink.net>
 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 *              Tom May, <ftom@netcom.com>
 *              Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>
 *              Lots of code moved from tcp.c and ip.c; see those files
 *              for more names.
 *
 * 03/02/96     Jes Sorensen, Andreas Schwab, Roman Hodek:
 *              Fixed some nasty bugs, causing some horrible crashes.
 *              A: At some points, the sum (%0) was used as
 *              length-counter instead of the length counter
 *              (%1). Thanks to Roman Hodek for pointing this out.
 *              B: GCC seems to mess up if one uses too many
 *              data-registers to hold input values and one tries to
 *              specify d0 and d1 as scratch registers. Letting gcc
 *              choose these registers itself solves the problem.
 */

/* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access
 kills, so most of the assembly has to go. */

#include <linux/export.h>
#include <net/checksum.h>

#include <asm/byteorder.h>

#ifndef do_csum
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;
}

static unsigned int do_csum(const unsigned char *buff, int len)
{
        int odd;
        unsigned int result = 0;

        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)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;
}
#endif

#ifndef ip_fast_csum
/*
 *      This is a version of ip_compute_csum() optimized for IP headers,
 *      which always checksum on 4 octet boundaries.
 */
__sum16 ip_fast_csum(const void *iph, unsigned int ihl)
{
        return (__force __sum16)~do_csum(iph, ihl*4);
}
EXPORT_SYMBOL(ip_fast_csum);
#endif

/*
 * computes the checksum of a memory block at buff, length len,
 * and adds in "sum" (32-bit)
 *
 * returns a 32-bit number suitable for feeding into itself
 * or csum_tcpudp_magic
 *
 * this function must be called with even lengths, except
 * for the last fragment, which may be odd
 *
 * it's best to have buff aligned on a 32-bit boundary
 */
__wsum csum_partial(const void *buff, int len, __wsum wsum)
{
        unsigned int sum = (__force unsigned int)wsum;
        unsigned int result = do_csum(buff, len);

        /* add in old sum, and carry.. */
        result += sum;
        if (sum > result)
                result += 1;
        return (__force __wsum)result;
}
EXPORT_SYMBOL(csum_partial);

/*
 * this routine is used for miscellaneous IP-like checksums, mainly
 * in icmp.c
 */
__sum16 ip_compute_csum(const void *buff, int len)
{
        return (__force __sum16)~do_csum(buff, len);
}
EXPORT_SYMBOL(ip_compute_csum);

/*
 * copy from fs while checksumming, otherwise like csum_partial
 */
__wsum
csum_partial_copy_from_user(const void __user *src, void *dst, int len,
                                                __wsum sum, int *csum_err)
{
        int missing;

        missing = __copy_from_user(dst, src, len);
        if (missing) {
                memset(dst + len - missing, 0, missing);
                *csum_err = -EFAULT;
        } else
                *csum_err = 0;

        return csum_partial(dst, len, sum);
}
EXPORT_SYMBOL(csum_partial_copy_from_user);

/*
 * copy from ds while checksumming, otherwise like csum_partial
 */
__wsum
csum_partial_copy(const void *src, void *dst, int len, __wsum sum)
{
        memcpy(dst, src, len);
        return csum_partial(dst, len, sum);
}
EXPORT_SYMBOL(csum_partial_copy);

#ifndef csum_tcpudp_nofold
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)
{
        unsigned long long s = (__force u32)sum;

        s += (__force u32)saddr;
        s += (__force u32)daddr;
#ifdef __BIG_ENDIAN
        s += proto + len;
#else
        s += (proto + len) << 8;
#endif
        return (__force __wsum)from64to32(s);
}
EXPORT_SYMBOL(csum_tcpudp_nofold);
#endif