PHP浮点数运算的问题

$a = 0.1;
$b = 0.7;
$c = 0.5;
$d = 0.9;
if ($a + $b == 0.8) {echo '==';} else {echo '!=';} // !=
if ($a + $c == 0.6) {echo '==';} else {echo '!=';} // ==
if ($a + $d == 1) {echo '==';} else {echo '!=';} // ==
if ($b + $c == 1.2) {echo '==';} else {echo '!=';} // ==

参考地址： https://www.cnblogs.com/hld123/p/14848530.html