exp

    (PHP 4, PHP 5, PHP 7, PHP 8)

    exp — e の累乗を計算する

    説明

    exp(float $num): float

    e を num 乗した値を返します。

    注意:

    'e' は自然対数の底で、およそ 2.718282 です。

    パラメータ

    num

    処理する引数。

    戻り値

    'e' の num 乗を返します。

    例

    例1 exp() の例

    <?php
    echo exp(12) . "\n";
    echo     exp(5.7);
    ?>

    上の例の出力は以下となります。

    1.6275E+005
298.87

    参考

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    User Contributed Notes 1 note

    up
    3
    zooly at globmi dot com
    14 years ago
    PHP does not have the following math function in any extensions:

    frexp() - Extract Mantissa and Exponent of the Floating-Point Value

    I've digged many C source codes, and found the simplest implementation as follows:

    <?php

    function frexp ( $float ) {

    $exponent = ( floor(log($float, 2)) + 1 );
    $mantissa = ( $float * pow(2, -$exponent) );

    return(
    array(    $mantissa, $exponent)
    );

    }

    print_r(frexp(0.0345));
    print_r(frexp(21.539));

    ?>

    Array
    (
    [0] => 0.552
    [1] => -4
    )
    Array
    (
    [0] => 0.67309375
    [1] => 5
    )

    I have compared the results using a lot of floats against C's frexp function - they are the same.

    Note that C and PHP uses different float precisions, for example "4619.3" gives:

    C: 0.56387939453125, 13
    PHP: 0.563879394531, 13

    /Assuming default configurations./
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