floor() in php not working

Question

<?php
    echo gettype ( 5.00 );                                  // return double
    echo gettype((5));                                      // return integer
    echo gettype(((167.00-158.65)/167.00*100));             // return double

    echo floor(5.00);                                       // return 5
    echo floor(5);                                          // return 5
    echo ((167.00-158.65)/167.00*100);                      // return 5
    echo floor(((167.00-158.65)/167.00*100));               // return 4



    var_dump(5.00);                                         // return float(5)
    var_dump(5);                                            // return int(5)
    var_dump((167.00-158.65)/167.00*100);                   // return float(5)
    var_dump(intval(5));                                    // return int(5)
    var_dump(intval((167.00-158.65)/167.00*100));           // return int(4)

    echo gettype(intval(((167.00-158.65)/167.00*100)));     // return integer
    echo floor(intval((167.00-158.65)/167.00*100));         // return 4
?>

Why floor function in php not working in last case?

How to get 5 from last statement? Is there any other function or method in php to get exact least amount?

Answer 1

That behaviour is caused by limited precision of floating point numbers. The last case is of type float (check it with var_dump), and the Manual says:

Warning

Floating point numbers have limited precision. Although it depends on the system, PHP typically uses the IEEE 754 double precision format, which will give a maximum relative error due to rounding in the order of 1.11e-16. Non elementary arithmetic operations may give larger errors, and, of course, error propagation must be considered when several operations are compounded.

Additionally, rational numbers that are exactly representable as floating point numbers in base 10, like 0.1 or 0.7, do not have an exact representation as floating point numbers in base 2, which is used internally, no matter the size of the mantissa. Hence, they cannot be converted into their internal binary counterparts without a small loss of precision. This can lead to confusing results: for example, floor((0.1+0.7)*10) will usually return 7 instead of the expected 8, since the internal representation will be something like 7.9999999999999991118....

Source:

http://php.net/manual/en/language.types.float.php