hexdigit
*hex++ = hexdigit(*bin >> 4);
*hex++ = hexdigit(*bin++ & 0xf);
static char hexdigit[] = "0123456789ABCDEF";
*c++ = hexdigit[b >> 4];
*c++ = hexdigit[b & 0xf];
static char hexdigit[] = "0123456789abcdef";
printf ("%c", hexdigit[*i >> 4]);
printf ("%c", hexdigit[*i % 16]);