i386/linux/linux-2.3.21/arch/alpha/lib/checksum.c

   1 /*
   2  * arch/alpha/lib/checksum.c
   3  *
   4  * This file contains network checksum routines that are better done
   5  * in an architecture-specific manner due to speed..
   6  */
   7
   8 #include <linux/string.h>
   9
  10 #include <asm/byteorder.h>
  11
  12 static inline unsigned short from64to16(unsigned long x)
  13 {
  14         /* add up 32-bit words for 33 bits */
  15         x = (x & 0xffffffff) + (x >> 32);
  16         /* add up 16-bit and 17-bit words for 17+c bits */
  17         x = (x & 0xffff) + (x >> 16);
  18         /* add up 16-bit and 2-bit for 16+c bit */
  19         x = (x & 0xffff) + (x >> 16);
  20         /* add up carry.. */
  21         x = (x & 0xffff) + (x >> 16);
  22         return x;
  23 }
  24
  25 /*
  26  * computes the checksum of the TCP/UDP pseudo-header
  27  * returns a 16-bit checksum, already complemented.
  28  */
  29 unsigned short int csum_tcpudp_magic(unsigned long saddr,
  30                                    unsigned long daddr,
  31                                    unsigned short len,
  32                                    unsigned short proto,
  33                                    unsigned int sum)
  34 {
  35         return ~from64to16(saddr + daddr + sum +
  36                 ((unsigned long) ntohs(len) << 16) +
  37                 ((unsigned long) proto << 8));
  38 }
  39
  40 unsigned int csum_tcpudp_nofold(unsigned long saddr,
  41                                    unsigned long daddr,
  42                                    unsigned short len,
  43                                    unsigned short proto,
  44                                    unsigned int sum)
  45 {
  46         unsigned long result;
  47
  48         result = (saddr + daddr + sum +
  49                   ((unsigned long) ntohs(len) << 16) +
  50                   ((unsigned long) proto << 8));
  51
  52         /* Fold down to 32-bits so we don't loose in the typedef-less
  53            network stack.  */
  54         /* 64 to 33 */
  55         result = (result & 0xffffffff) + (result >> 32);
  56         /* 33 to 32 */
  57         result = (result & 0xffffffff) + (result >> 32);
  58         return result;
  59 }
  60
  61 /*
  62  * Do a 64-bit checksum on an arbitrary memory area..
  63  *
  64  * This isn't a great routine, but it's not _horrible_ either. The
  65  * inner loop could be unrolled a bit further, and there are better
  66  * ways to do the carry, but this is reasonable.
  67  */
  68 static inline unsigned long do_csum(const unsigned char * buff, int len)
  69 {
  70         int odd, count;
  71         unsigned long result = 0;
  72
  73         if (len <= 0)
  74                 goto out;
  75         odd = 1 & (unsigned long) buff;
  76         if (odd) {
  77                 result = *buff << 8;
  78                 len--;
  79                 buff++;
  80         }
  81         count = len >> 1;               /* nr of 16-bit words.. */
  82         if (count) {
  83                 if (2 & (unsigned long) buff) {
  84                         result += *(unsigned short *) buff;
  85                         count--;
  86                         len -= 2;
  87                         buff += 2;
  88                 }
  89                 count >>= 1;            /* nr of 32-bit words.. */
  90                 if (count) {
  91                         if (4 & (unsigned long) buff) {
  92                                 result += *(unsigned int *) buff;
  93                                 count--;
  94                                 len -= 4;
  95                                 buff += 4;
  96                         }
  97                         count >>= 1;    /* nr of 64-bit words.. */
  98                         if (count) {
  99                                 unsigned long carry = 0;
 100                                 do {
 101                                         unsigned long w = *(unsigned long *) buff;
 102                                         count--;
 103                                         buff += 8;
 104                                         result += carry;
 105                                         result += w;
 106                                         carry = (w > result);
 107                                 } while (count);
 108                                 result += carry;
 109                                 result = (result & 0xffffffff) + (result >> 32);
 110                         }
 111                         if (len & 4) {
 112                                 result += *(unsigned int *) buff;
 113                                 buff += 4;
 114                         }
 115                 }
 116                 if (len & 2) {
 117                         result += *(unsigned short *) buff;
 118                         buff += 2;
 119                 }
 120         }
 121         if (len & 1)
 122                 result += *buff;
 123         result = from64to16(result);
 124         if (odd)
 125                 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
 126 out:
 127         return result;
 128 }
 129
 130 /*
 131  *      This is a version of ip_compute_csum() optimized for IP headers,
 132  *      which always checksum on 4 octet boundaries.
 133  */
 134 unsigned short ip_fast_csum(unsigned char * iph, unsigned int ihl)
 135 {
 136         return ~do_csum(iph,ihl*4);
 137 }
 138
 139 /*
 140  * computes the checksum of a memory block at buff, length len,
 141  * and adds in "sum" (32-bit)
 142  *
 143  * returns a 32-bit number suitable for feeding into itself
 144  * or csum_tcpudp_magic
 145  *
 146  * this function must be called with even lengths, except
 147  * for the last fragment, which may be odd
 148  *
 149  * it's best to have buff aligned on a 32-bit boundary
 150  */
 151 unsigned int csum_partial(const unsigned char * buff, int len, unsigned int sum)
 152 {
 153         unsigned long result = do_csum(buff, len);
 154
 155         /* add in old sum, and carry.. */
 156         result += sum;
 157         /* 32+c bits -> 32 bits */
 158         result = (result & 0xffffffff) + (result >> 32);
 159         return result;
 160 }
 161
 162 /*
 163  * this routine is used for miscellaneous IP-like checksums, mainly
 164  * in icmp.c
 165  */
 166 unsigned short ip_compute_csum(unsigned char * buff, int len)
 167 {
 168         return ~from64to16(do_csum(buff,len));
 169 }