ipv6_u.c

   1 /*
   2  * Fernando ALVES 2014
   3  * GPL licenced
   4  */
   5
   6 #include <arpa/inet.h>
   7
   8 #include "ipv6_u.h"
   9
  10 uint16_t ipv6_checksum(struct ipv6_pseudo_hdr *p_pshdr, uint8_t *buff, int lenbuff)
  11 {
  12         uint32_t sum = 0;
  13         uint16_t *ptrw = (uint16_t *) p_pshdr;
  14         uint16_t word16;
  15         int i;
  16
  17         // Size pseudo header 40 byte (20 word)
  18         for (i = 0; i < (sizeof(*p_pshdr)/2); i++)
  19         {
  20                 word16 = ntohs(*((uint16_t *)ptrw));
  21                 sum += word16;
  22                 ++ptrw;
  23         }
  24
  25         ptrw = (uint16_t *) buff;
  26         while (lenbuff > 1)
  27         {
  28                 word16 = ntohs(*((uint16_t *) ptrw));
  29                 sum += word16;
  30                 ++ptrw;
  31                 lenbuff -= 2;
  32         }
  33
  34         if (lenbuff > 0)
  35         {
  36                 word16 = ntohs(*((uint8_t *) ptrw));
  37                 sum += word16;
  38         }
  39
  40         // take only 16 bits out of the 32 bit sum and add up the carries
  41         while (sum >> 16)
  42                 sum = (sum & 0xFFFF) + (sum >> 16);
  43
  44         // one's complement the result
  45         sum = ~sum;
  46
  47         return htons((uint16_t) sum);
  48 }