sys/src/9/ip/ptclbsum.c

   1 #include        "u.h"
   2 #include        "../port/lib.h"
   3 #include        "mem.h"
   4 #include        "dat.h"
   5 #include        "fns.h"
   6 #include        "../port/error.h"
   7 #include        "ip.h"
   8
   9 static  short   endian  = 1;
  10 static  uchar*  aendian = (uchar*)&endian;
  11 #define LITTLE  *aendian
  12
  13 ushort
  14 ptclbsum(uchar *addr, int len)
  15 {
  16         ulong losum, hisum, mdsum, x;
  17         ulong t1, t2;
  18
  19         losum = 0;
  20         hisum = 0;
  21         mdsum = 0;
  22
  23         x = 0;
  24         if((ulong)addr & 1) {
  25                 if(len) {
  26                         hisum += addr[0];
  27                         len--;
  28                         addr++;
  29                 }
  30                 x = 1;
  31         }
  32         while(len >= 16) {
  33                 t1 = *(ushort*)(addr+0);
  34                 t2 = *(ushort*)(addr+2);        mdsum += t1;
  35                 t1 = *(ushort*)(addr+4);        mdsum += t2;
  36                 t2 = *(ushort*)(addr+6);        mdsum += t1;
  37                 t1 = *(ushort*)(addr+8);        mdsum += t2;
  38                 t2 = *(ushort*)(addr+10);       mdsum += t1;
  39                 t1 = *(ushort*)(addr+12);       mdsum += t2;
  40                 t2 = *(ushort*)(addr+14);       mdsum += t1;
  41                 mdsum += t2;
  42                 len -= 16;
  43                 addr += 16;
  44         }
  45         while(len >= 2) {
  46                 mdsum += *(ushort*)addr;
  47                 len -= 2;
  48                 addr += 2;
  49         }
  50         if(x) {
  51                 if(len)
  52                         losum += addr[0];
  53                 if(LITTLE)
  54                         losum += mdsum;
  55                 else
  56                         hisum += mdsum;
  57         } else {
  58                 if(len)
  59                         hisum += addr[0];
  60                 if(LITTLE)
  61                         hisum += mdsum;
  62                 else
  63                         losum += mdsum;
  64         }
  65
  66         losum += hisum >> 8;
  67         losum += (hisum & 0xff) << 8;
  68         while(hisum = losum>>16)
  69                 losum = hisum + (losum & 0xffff);
  70
  71         return losum & 0xffff;
  72 }