function generate_attack_senquence($a,$b)
{
    $a_count = $b_count = 0;
    $a_rate = 1.0/$a;
    $b_rate = 1.0/$b;

    while(true)
    {
        $diff = ($a_rate + $a_count) - ($b_rate + $b_count);
        if($diff < -1e-8)
        {
            print 'A ';
            $a_count += $a_rate;
        }
        else if(-1e-8 <= $diff && 1e-8 >= $diff)
        {
            $a_count += $a_rate;
            $b_count += $b_rate;
            print 'A|B ';
        }
        else
        {
            $b_count += $b_rate;
            print 'B ';
        }
    }
}

中间把-1e-8~1e-8之间的浮点值认为是0，因为程序中的浮点数的精度都是有限的。举个例子：

$onethird = 1.0/3;
$fivethirds = 1.0/3+1.0/3+1.0/3+1.0/3+1.0/3;
$half = 1.0/2;
$threehalf = 1.0/2+1.0/2+1.0/2;
var_dump($onethird + $fivethirds == $half + $threehalf);

上面这段程序将输出false，而实际上5/3+1/3=3/2+1/2=2。解决是：

var_dump(($onethird + $fivethirds) - ($half + $threehalf) > -1e-8 && ($onethird + $fivethirds) - ($half + $threehalf) < 1e-8);