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Trying to understand this code behavior

I was working on a PHP project today and came across this code behavior

<?php
$x = 5.5;
$y = 0;
echo $z = floor($x * $y * -1);
?>

This worked -0

. Can anyone shed some light on why this is repeating -0

. But I expected that 0

Only when adding a floor does this seem to happen. I have tried the same in java.

class Sample {
    public static void main(String[] args) {
        float x =5.5f;
        int y = 0;
        System.out.println(Math.floor(x*y*-1));
    }
}

This also prints -0.0

.

+3


source to share


2 answers


float

and double

have both positive 0s and negative 0s. When you multiple 0 * -1, you get -0, as specified in the IEEE 754 standard.

Note: 1/0 is positive infinity, but 1 / -0 is negative infinity.

You can see that http://ideone.com/tBd41l

System.out.println(0f * -1);


prints

-0.0

Math.floor is not required.

+3


source


As PHP floor()

returns float (for some reason) and float is allowed to have negative 0.

This gives a normal 0:



$x = 5.5;
$y = 0;
echo $z = floor($x * $y * -1 * -1);
+1


source






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