The following code will convert an ethernet MAC address to the comparable  IPv6 link only address.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdarg.h>

int main(int argc, char** argv){

int addrlen = strlen(“0000:0000:0000:0000:0000:0000:0000:”);
char* out = malloc(addrlen);
char * outorig = out;

memset(out, 0, addrlen);

char* addr =    “00:0c:29:20:4e:e3″;

if (argc > 1){
addr = argv[1];
}else{
fprintf(stderr,”usage %s macaddr\n”,argv[0]);
exit(-1);
}

int len = strlen(addr);

if (len > 18){
printf (“String too long\n”);
exit(-1);
}

int i ;
int col_count = 0;
unsigned char current = 0;
for (i = 0; i < len; ++i){
char c = addr[i];

if (0 == c){
break;
}else if (‘:’ == c){
switch( col_count ){
case 0:{
sprintf(out,”fe80::”);
out += strlen(out);

unsigned short c2 = ( current | 0x02 );
if (c2 == current){
c2 = current & 0xcf;
}
sprintf(out,”%02x”,c2);
out += strlen(out);
}
break;
case 2:{
sprintf(out,”%02xff:fe”,current);
out += strlen(out);
}
break;
default:
sprintf(out,”%02x”,current);
out += strlen(out);

if (col_count % 2){
sprintf(out,”:”);
out += strlen(out);
}
}
++col_count;
current = 0;
}else if ((c >= ‘a’) && (c <= ‘f’)){
current *=16;
current += ( 10 + c – ‘a’);
}else if ((c >= ‘A’) && (c <= ‘F’)){
current *=16;
current += ( 10 + c – ‘a’);
}else if ((c >= ‘0’) && (c <= ‘9’)){
current *=16;
current += ( c – ‘0’);
}
}

sprintf(out,”%x”,current);
out += strlen(out);
printf(outorig);
return 0;

}