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    定義済み定数

    以下の定数は、PHP コアに含まれており、常に利用可能です。

    数学関連の定数
    M_PI (float)
    π (pi) の近似値 (3.14159265358979323846).
    M_E (float)
    Euler数 e の近似値 (2.7182818284590452354).
    M_LOG2E (float)
    log2(e) の近似値 (1.4426950408889634074).
    M_LOG10E (float)
    log10(e) の近似値 (0.43429448190325182765).
    M_LN2 (float)
    ln(2) の近似値 (0.69314718055994530942).
    M_LN10 (float)
    ln(10) の近似値 (2.30258509299404568402).
    M_PI_2 (float)
    π/2 の近似値 (1.57079632679489661923).
    M_PI_4 (float)
    π/4 の近似値 (0.78539816339744830962).
    M_1_PI (float)
    1/π の近似値 (0.31830988618379067154).
    M_2_PI (float)
    2/π の近似値 (0.63661977236758134308).
    M_SQRTPI (float)
    sqrt(π) の近似値 (1.77245385090551602729).
    M_2_SQRTPI (float)
    2/sqrt(π) の近似値 (1.12837916709551257390).
    M_SQRT2 (float)
    sqrt(2) の近似値 (1.41421356237309504880).
    M_SQRT3 (float)
    sqrt(3) の近似値 (1.73205080756887729352).
    M_SQRT1_2 (float)
    1/sqrt(2) の近似値 (0.70710678118654752440).
    M_LNPI (float)
    ln(π) の近似値 (1.14472988584940017414).
    M_EULER (float)
    Euler's constant γ の近似値 (0.57721566490153286061).
    IEEE 754 浮動小数点数の定数
    NAN (float)
    Not A Number
    INF (float)
    Infinity
    丸め定数

    注意: PHP 8.4.0 以降は、 RoundingMode enum を代わりに使うことを推奨します。

    PHP_ROUND_HALF_UP (int)
    ゼロから離れる方向に丸めます。
    PHP_ROUND_HALF_DOWN (int)
    ゼロに近づく方向に丸めます。
    PHP_ROUND_HALF_EVEN (int)
    もっとも近い偶数に丸めます。
    PHP_ROUND_HALF_ODD (int)
    もっとも近い奇数に丸めます。

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    User Contributed Notes 4 notes

    up
    39
    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'
    up
    18
    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.
    up
    6
    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)
    ?>
    up
    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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