bcpow

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

    bcpow — Raise an arbitrary precision number to another

    Description

    bcpow(string $num, string $exponent, ?int $scale = null): string

    Raise num to the power exponent.

    Parameters

    num

    The base, as a string.

    exponent

    The exponent, as a string. If the exponent is non-integral, it is truncated. The valid range of the exponent is platform specific, but is at least -2147483648 to 2147483647.

    scale

    This optional parameter is used to set the number of digits after the decimal place in the result. If omitted, it will default to the scale set globally with the bcscale() function, or fallback to 0 if this has not been set.

    Return Values

    Returns the result as a string.

    Changelog

    Version Description
    7.3.0 bcpow() now returns numbers with the requested scale. Formerly, the returned numbers may have omitted trailing decimal zeroes.

    Examples

    Example #1 bcpow() example

    <?php

    echo bcpow('4.2', '3', 2); // 74.08

    ?>

    Notes

    Note:

    Before PHP 7.3.0 bcpow() may return a result with fewer digits after the decimal point than the scale parameter would indicate. This only occurs when the result doesn't require all of the precision allowed by the scale. For example:

    Example #2 bcpow() scale example

    <?php
    echo bcpow('5', '2', 2); // prints "25", not "25.00"
    ?>

    See Also

    • bcpowmod() - Raise an arbitrary precision number to another, reduced by a specified modulus
    • bcsqrt() - Get the square root of an arbitrary precision number

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    User Contributed Notes 3 notes

    up
    -1
    thomas at tgohome dot com
    15 years ago
    <?php

    bcscale    (100);

    /*
    * Computes the natural logarithm using a series.
    * @author Thomas Oldbury.
    * @license Public domain.
    */
    function bcln($a, $iter = 10)
    {
    $result = "0.0";

    for(    $i = 0; $i < $iter; $i++)
    {
    $pow = (1 + (2 * $i));
    $mul = bcdiv("1.0", $pow);
    $fraction = bcmul($mul, bcpow(bcsub($a, "1.0") / bcadd($a, "1.0"), $pow));
    $result = bcadd($fraction, $result);
    }

    return     bcmul("2.0", $result);
    }

    /*
    * Computes the base2 log using baseN log.
    * @note Requires above functions.
    * @author Thomas Oldbury.
    * @license Public domain.
    */
    function bclog2($a, $iter = 10)
    {
    return     bcdiv(bcln($a, $iter), bcln("2", $iter));
    }

    /*
    * Computes the base10 log using baseN log.
    * @note Requires above functions.
    * @author Thomas Oldbury.
    * @license Public domain.
    */
    function bclog10($a, $iter = 10)
    {
    return     bcdiv(bcln($a, $iter), bcln("10", $iter));
    }


    ?>
    up
    -2
    Anonymous
    19 years ago
    Well, if bcpow has limits, then this should work:
    <?php
    function bcpow_($num, $power) {
    $awnser = "1";
    while (    $power) {
    $awnser = bcmul($awnser, $num, 100);
    $power = bcsub($power, "1");
    }
    return     rtrim($awnser, '0.');
    }
    ?>
    Just that $power cannot have decimal digits in it.
    up
    -2
    Michael Bailey (jinxidoru at byu dot net)
    20 years ago
    bcpow() only supports exponents less than or equal to 2^31-1. Also, bcpow() does not support decimal numbers. If you have scale set to 0, then the exponent is converted to an interger; otherwise an error is generated.

    --
    Michael Bailey
    http://www.jinxidoru.com
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