Description:
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First of all: I am aware of how floats work and that they are only approximations of their ideal values.

I found an inconsistency in how they are handled when added, please see the code below. Variable $a and $b are created by summing up three floats <1.0. The only difference is the order of the summands. Both variables should have exactly the same value, yet $a evaluates to 1.0 and $b to <1.0.

Test script:
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<?php

$a = array_sum(array(0.6, 0.3, 0.1));
$b = array_sum(array(0.1, 0.3, 0.6));

var_dump($a); // float(1)
var_dump($b); // float(1)
var_dump($a == $b); // bool(false)
var_dump(intval($a)); // int(0)
var_dump(intval($b)); // int(1)

$c = $a - 1;
var_dump($c); // float(-1.1102230246252E-16)


Expected result:
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float(1)
float(1)
bool(true)
int(1)
int(1)
float(0)

Actual result:
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float(1)
float(1)
bool(false)
int(0)
int(1)
float(-1.1102230246252E-16)