int
iso_csum_verify (u_char * buffer, int len, uint16_t * csum)
{
u_int16_t checksum;
u_int32_t c0;
u_int32_t c1;
c0 = *csum & 0xff00;
c1 = *csum & 0x00ff;
/*
* If both are zero return correct
*/
if (c0 == 0 && c1 == 0)
return 0;
/*
* If either, but not both are zero return incorrect
*/
if (c0 == 0 || c1 == 0)
return 1;
/* Offset of checksum from the start of the buffer */
int offset = (u_char *) csum - buffer;
checksum = fletcher_checksum(buffer, len, offset);
if (checksum == *csum)
return 0;
return 1;
}
int
ospf_lsa_checksum_valid (struct lsa_header *lsa)
{
u_char *buffer = (u_char *) &lsa->options;
int options_offset = buffer - (u_char *) &lsa->ls_age; /* should be 2 */
/* Skip the AGE field */
u_int16_t len = ntohs(lsa->length) - options_offset;
return(fletcher_checksum(buffer, len, FLETCHER_CHECKSUM_VALIDATE) == 0);
}
u_int16_t
ospf_lsa_checksum (struct lsa_header *lsa)
{
u_char *buffer = (u_char *) &lsa->options;
int options_offset = buffer - (u_char *) &lsa->ls_age; /* should be 2 */
/* Skip the AGE field */
u_int16_t len = ntohs(lsa->length) - options_offset;
/* Checksum offset starts from "options" field, not the beginning of the
lsa_header struct. The offset is 14, rather than 16. */
int checksum_offset = (u_char *) &lsa->checksum - buffer;
return fletcher_checksum(buffer, len, checksum_offset);
}