hexdigit
char hexdigit[] = "0123456789abcdef";
*outb++ = hexdigit[*inb >> 4];
*outb++ = hexdigit[*inb++ & 0xf];
if (!hexdigit(in[0]))
if (hexdigit(in[1]))
*hex++ = hexdigit(*bin >> 4);
*hex++ = hexdigit(*bin++ & 0xf);