Why is gender (0.9999999999999999999) = 1 and gender (0.9999999999999999) = 0?

Question

The floor function in PHP behaves strangely. For 16 decimal values, it gives the value of the sexes, but increasing 1 decimal digit.

$int = 0.99999999999999999; 
echo floor($int); // returns 1 

$int = 0.9999999999999999; 
echo floor($int); // returns 0

$int = 0.99999999999999994; 
echo floor($int); // returns 0

• Is it defined / explained somewhere, and at what point does it give a “round” meaning?
• Is there any function that gives one 0way or another how many 9 decimal places?

Answer 1

It is not floorthat rounds, it is the floating point math that does.

This line:

echo 0.99999999999999999;

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Answer 2

$float_14_digits = 0.99999999999999;
echo $float_14_digits; // prints 0.99999999999999
echo floor($float_14_digits); // prints 0

$float_15_digits = 0.999999999999999;
echo $float_15_digits; // prints 1
echo floor($float_15_digits); // prints 1
exit;

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