FreeBSD/Linux Kernel Cross Reference
sys/lib/checksum.c

     /*
      *
      * 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.
     *
     *              This program is free software; you can redistribute it and/or
     *              modify it under the terms of the GNU General Public License
     *              as published by the Free Software Foundation; either version
     *              2 of the License, or (at your option) any later version.
     */
    
    /* 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
   
   /*
    *      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);
   
   /*
    * 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
   __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
                           unsigned short len,
                           unsigned short 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
           s += (s >> 32);
           return (__force __wsum)s;
   }
   EXPORT_SYMBOL(csum_tcpudp_nofold);
   #endif

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