hexchar2int
static int hexchar2int( char c );
if ( hexchar2int(s[0]) >= 0 && hexchar2int(s[1]) >= 0 ) ++s;
if (( ival = hexchar2int( *s )) < 0 ) {
static int hexchar2int(char c);
if (hexchar2int(s[0]) >= 0 && hexchar2int(s[1]) >= 0)
if (hexchar2int(*s) < 0) {