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    Constantes predefinidas

    Estas constantes están disponibles siempre ya que forman parte del núcleo de PHP.

    Constantes matemáticas
    Constante Valor Descripción Disponibilidad
    M_PI 3.14159265358979323846 Pi  
    M_E 2.7182818284590452354 e  
    M_LOG2E 1.4426950408889634074 log_2 e  
    M_LOG10E 0.43429448190325182765 log_10 e  
    M_LN2 0.69314718055994530942 log_e 2  
    M_LN10 2.30258509299404568402 log_e 10  
    M_PI_2 1.57079632679489661923 pi/2  
    M_PI_4 0.78539816339744830962 pi/4  
    M_1_PI 0.31830988618379067154 1/pi  
    M_2_PI 0.63661977236758134308 2/pi  
    M_SQRTPI 1.77245385090551602729 sqrt(pi) PHP 5.2.0
    M_2_SQRTPI 1.12837916709551257390 2/sqrt(pi)  
    M_SQRT2 1.41421356237309504880 sqrt(2)  
    M_SQRT3 1.73205080756887729352 sqrt(3) PHP 5.2.0
    M_SQRT1_2 0.70710678118654752440 1/sqrt(2)  
    M_LNPI 1.14472988584940017414 log_e(pi) PHP 5.2.0
    M_EULER 0.57721566490153286061 Constante de Euler PHP 5.2.0
    PHP_ROUND_HALF_UP 1 Redondeo al siguiente medio superior PHP 5.3.0
    PHP_ROUND_HALF_DOWN 2 Redondeo al medio inferior PHP 5.3.0
    PHP_ROUND_HALF_EVEN 3 Redondeo de las mitades de números pares PHP 5.3.0
    PHP_ROUND_HALF_ODD 4 Redondeo de las mitades de números impares PHP 5.3.0
    NAN NAN (como float) No es un numero (NAN=Not A Number)  
    INF INF (como float) Infinito  

    Todas las constantes sin una versión de PHP indicada están disponibles desde la PHP 5.0.0.

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    User Contributed Notes 7 notes

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    35
    md2perpe at gmail dot com
    9 years ago
    I just learnt of INF today and found out that it can be used in comparisons:

        echo 5000 < INF ? 'yes' : 'no';       // outputs 'yes'
        echo INF < INF ? 'yes' : 'no';        // outputs 'no'
        echo INF <= INF ? 'yes' : 'no';       // outputs 'yes'
        echo INF == INF ? 'yes' : 'no';       // outputs 'yes'

    You can also take its negative:

        echo -INF < -5000 ? 'yes' : 'no';    // outputs 'yes'

    Division by INF is allowed:

        echo 1/INF;    // outputs '0'
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    17
    Hayley Watson
    12 years ago
    There are also the predefined PHP_INT_MAX and PHP_INT_SIZE constants, that describe the range of possible integer values.
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    7
    pemapmodder1970 at gmail dot com
    8 years ago
    Although INF can be used for comparison against normal numbers and as a directed number, and behaves as reciprocal of zero, it is not like limit INF tends to infinity. These operations do not work:

    <?php
    var_dump    (INF / INF); // float(NAN)
    var_dump(INF - INF); // float(NAN)
    ?>

    However, it works with arc-tangent:
    <?php
    var_dump    (atan(INF) / M_PI); // float(0.5)
    var_dump(atan2(INF, INF) / M_PI); // float(0.25)
    var_dump(atan2(1, INF) / M_PI); // float(0)
    ?>
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    2
    Hayley Watson
    7 years ago
    From PHP 7.2.0, the PHP_FLOAT_* constants are provided to describe the properties of floating point numbers that can be stored; PHP_FLOAT_MAX, for example, is analogous to PHP_INT_MAX and represents the largest possible floating-point number.
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    0
    br at ndon dot co
    3 years ago
    The constants

    PHP_ROUND_HALF_UP
    PHP_ROUND_HALF_DOWN
    PHP_ROUND_HALF_EVEN
    PHP_ROUND_HALF_ODD

    are constants intended to be used as the 3rd parameter in the math function round()

    https://www.php.net/manual/en/function.round
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    0
    steve at websmithery dot co dot uk
    7 years ago
    Another observation on INF.

    Division by zero results in INF:

    <?php
    var_dump    (1/0); // float(INF)
    ?>

    BUT a 'Division by zero' warning is issued.
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    -2
    Kira-Bianca dot Hinz at web dot de
    4 years ago
    Caution when using variables with the value NAN (or directly NAN, which would not be logical) if the value is converted in any form (integer, string or other non-float format)!
    In that case, NAN is converted to 0. (e.g. as an index in an array, argument of a method that takes it as a non-float parameter, etc.). This bug has been reported several times, but is still present in the current version PHP 7.3.15.

    Example 1:
    $array = [0 =>  'zero', 1 => 'one', 2 => 'two'];
    $index = NAN;
    echo $array[$index]; // echo 'zero' and not as axcepted throws an exception or at least a warning 'undefined offset NAN ...'

    Example 2:
    function f((int) $p) { return $p; }
    echo f(NAN); // echo 0 because the argument (NAN) has been converted to integer (0)

    It would have to be checked in both cases explicitly for is_nan():
    1: if(is_nan($index)){
          <throw Exception>
       }else{
          echo $array[$index];
       };

    2: function f($p){ // without converting!!!
          if(is_nan($p)){
             <throw Exception>
          }else{
             return (int)$p; // actually a correct conversion  to Integer would have to be checked because the parser does not check this here.
          };
       }
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