LXR linux/lib/checksum.c

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 *
   4 * INET         An implementation of the TCP/IP protocol suite for the LINUX
   5 *              operating system.  INET is implemented using the  BSD Socket
   6 *              interface as the means of communication with the user level.
   7 *
   8 *              IP/TCP/UDP checksumming routines
   9 *
  10 * Authors:     Jorge Cwik, <jorge@laser.satlink.net>
  11 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  12 *              Tom May, <ftom@netcom.com>
  13 *              Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>
  14 *              Lots of code moved from tcp.c and ip.c; see those files
  15 *              for more names.
  16 *
  17 * 03/02/96     Jes Sorensen, Andreas Schwab, Roman Hodek:
  18 *              Fixed some nasty bugs, causing some horrible crashes.
  19 *              A: At some points, the sum (%0) was used as
  20 *              length-counter instead of the length counter
  21 *              (%1). Thanks to Roman Hodek for pointing this out.
  22 *              B: GCC seems to mess up if one uses too many
  23 *              data-registers to hold input values and one tries to
  24 *              specify d0 and d1 as scratch registers. Letting gcc
  25 *              choose these registers itself solves the problem.
  26 */
  27
  28/* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access
  29 kills, so most of the assembly has to go. */
  30
  31#include <linux/export.h>
  32#include <net/checksum.h>
  33
  34#include <asm/byteorder.h>
  35
  36#ifndef do_csum
  37static inline unsigned short from32to16(unsigned int x)
  38{
  39        /* add up 16-bit and 16-bit for 16+c bit */
  40        x = (x & 0xffff) + (x >> 16);
  41        /* add up carry.. */
  42        x = (x & 0xffff) + (x >> 16);
  43        return x;
  44}
  45
  46static unsigned int do_csum(const unsigned char *buff, int len)
  47{
  48        int odd;
  49        unsigned int result = 0;
  50
  51        if (len <= 0)
  52                goto out;
  53        odd = 1 & (unsigned long) buff;
  54        if (odd) {
  55#ifdef __LITTLE_ENDIAN
  56                result += (*buff << 8);
  57#else
  58                result = *buff;
  59#endif
  60                len--;
  61                buff++;
  62        }
  63        if (len >= 2) {
  64                if (2 & (unsigned long) buff) {
  65                        result += *(unsigned short *) buff;
  66                        len -= 2;
  67                        buff += 2;
  68                }
  69                if (len >= 4) {
  70                        const unsigned char *end = buff + ((unsigned)len & ~3);
  71                        unsigned int carry = 0;
  72                        do {
  73                                unsigned int w = *(unsigned int *) buff;
  74                                buff += 4;
  75                                result += carry;
  76                                result += w;
  77                                carry = (w > result);
  78                        } while (buff < end);
  79                        result += carry;
  80                        result = (result & 0xffff) + (result >> 16);
  81                }
  82                if (len & 2) {
  83                        result += *(unsigned short *) buff;
  84                        buff += 2;
  85                }
  86        }
  87        if (len & 1)
  88#ifdef __LITTLE_ENDIAN
  89                result += *buff;
  90#else
  91                result += (*buff << 8);
  92#endif
  93        result = from32to16(result);
  94        if (odd)
  95                result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
  96out:
  97        return result;
  98}
  99#endif
 100
 101#ifndef ip_fast_csum
 102/*
 103 *      This is a version of ip_compute_csum() optimized for IP headers,
 104 *      which always checksum on 4 octet boundaries.
 105 */
 106__sum16 ip_fast_csum(const void *iph, unsigned int ihl)
 107{
 108        return (__force __sum16)~do_csum(iph, ihl*4);
 109}
 110EXPORT_SYMBOL(ip_fast_csum);
 111#endif
 112
 113/*
 114 * computes the checksum of a memory block at buff, length len,
 115 * and adds in "sum" (32-bit)
 116 *
 117 * returns a 32-bit number suitable for feeding into itself
 118 * or csum_tcpudp_magic
 119 *
 120 * this function must be called with even lengths, except
 121 * for the last fragment, which may be odd
 122 *
 123 * it's best to have buff aligned on a 32-bit boundary
 124 */
 125__wsum csum_partial(const void *buff, int len, __wsum wsum)
 126{
 127        unsigned int sum = (__force unsigned int)wsum;
 128        unsigned int result = do_csum(buff, len);
 129
 130        /* add in old sum, and carry.. */
 131        result += sum;
 132        if (sum > result)
 133                result += 1;
 134        return (__force __wsum)result;
 135}
 136EXPORT_SYMBOL(csum_partial);
 137
 138/*
 139 * this routine is used for miscellaneous IP-like checksums, mainly
 140 * in icmp.c
 141 */
 142__sum16 ip_compute_csum(const void *buff, int len)
 143{
 144        return (__force __sum16)~do_csum(buff, len);
 145}
 146EXPORT_SYMBOL(ip_compute_csum);
 147
 148#ifndef csum_tcpudp_nofold
 149static inline u32 from64to32(u64 x)
 150{
 151        /* add up 32-bit and 32-bit for 32+c bit */
 152        x = (x & 0xffffffff) + (x >> 32);
 153        /* add up carry.. */
 154        x = (x & 0xffffffff) + (x >> 32);
 155        return (u32)x;
 156}
 157
 158__wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
 159                          __u32 len, __u8 proto, __wsum sum)
 160{
 161        unsigned long long s = (__force u32)sum;
 162
 163        s += (__force u32)saddr;
 164        s += (__force u32)daddr;
 165#ifdef __BIG_ENDIAN
 166        s += proto + len;
 167#else
 168        s += (proto + len) << 8;
 169#endif
 170        return (__force __wsum)from64to32(s);
 171}
 172EXPORT_SYMBOL(csum_tcpudp_nofold);
 173#endif
 174