srand( 711 );

  . . .

  sub case2
  {  my $s1 = 'a' x 39 . 'b';
     my $s2 = 'a' x 39 . chr( 98 + rand(4));
     my ( $cmp, $loc ) = Cmp_and_Loc ( $s1, $s2 );
  }

  sub Cmp_and_Loc
  { my ( $s1, $s2, undef ) = @_;
    my $t = 0;
    my $cmp = $s1 cmp $s2;
    if ( $cmp ) { $t = $s1 ^ $s2; $t =~ /^\0*)/; $t = $+[0]; }
    return ( $cmp, $t );
  }