sys/src/libip/ptclbsum.c

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