gmp_init

    (PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)

    gmp_init — Create GMP number

    Description

    gmp_init(int|string $num, int $base = 0): GMP

    Creates a GMP number from an integer or string.

    Parameters

    num
    An integer or a string. The string representation can be decimal, hexadecimal, octal, or binary.
    base
    The base to use for converting a string representation. An explicit base can be between 2 and 62. For bases up to 36, case is ignored; upper-case and lower-case letters have the same value. For bases 37 to 62, upper-case letter represent the values 10 to 35 and lower-case letter represent the values 36 to 61. If base is 0 then the actual base is determined from the leading characters of num. If the first two characters are 0x or 0X, the string is interpreted as a hexadecimal integer. If the first two characters are 0b or 0B, the string is interpreted as a binary integer. If the first two characters are 0o or 0o, the string is interpreted as an octal integer. Moreover, if the first character is 0 the string is also interpreted as an octal integer. In all other cases, the string is interpreted as a decimal integer.

    Return Values

    A GMP object.

    Changelog

    Version Description
    8.1.0 Support for explicit octal prefixes 0o and 0o has been added for num strings. Interpretation of such prefixes when base is 0 has also been added.

    Examples

    Example #1 Creating GMP number

    <?php
    $a     = gmp_init(123456);
    $b = gmp_init("0xFFFFDEBACDFEDF7200");
    ?>

    Notes

    Note:

    It is not necessary to call this function in order to use integers or strings in place of GMP numbers in GMP functions (such as with gmp_add()). Function arguments are automatically converted to GMP numbers, if such conversion is possible and needed, using the same rules as gmp_init().

    See Also

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    User Contributed Notes 7 notes

    up
    4
    php at richardneill dot org
    18 years ago
    Here's a way to parse a decimal (eg 3.25) into an integer and exponent:

    <?
    if (preg_match("/^[0-9]+\.[0-9]+$/",$input)){
    //Input is a base-10 decimal. Multiply as necessary to remove the decimal
    //point. Convert that to a gmp_resource, then decrement the exponent
    //to compensate.

    $pieces=explode(".", $input); //Split at the d.p.
    $input="$pieces[0]$pieces[1]"; //Remove the decimal point.

    $input=ltrim($input,'0');
    //Remove any leading zeros, or gmp_init will parse the number as octal.

    if ($input==''){ //Deal with "0.0" which would otherwise be ''.
    $input=0;
    }
    $integer=gmp_init($input);
    $ns_exponent=-strlen($pieces[1]);
    //exponent = (-) the number of characters after the decimal point.
    }
    ?>
    up
    2
    karl dot debisschop at pearson dot com
    13 years ago
    Unless the base is 16, gpm_init will fail if the string begins with "0b".

    > php -r '$v = gmp_init("b83", 17); print("$v\n");'

    Resource id #4

    > php -r '$v = gmp_init("0b83", 17); print("$v\n");'

    [nothing prints]

    In may case, where I am explicitly specifying the base, the solution is to apply ltrim first:

    > php -r '$v = gmp_init(ltrim("0b83", "0"), 17); print("$v\n");'

    Resource id #4
    up
    2
    marcus at synchromedia dot co dot uk
    13 years ago
    I discovered that the gmp functions use [0-9a-f] up to base 16, but [0-9A-Za-z] (i.e. upper case first) from bases 17 to 62. This differs from most of the base-62 implementations I've found that tend to use lower case first.
    up
    1
    php at richardneill dot org
    18 years ago
    Note: Leading zeros will make gmp_init parse this as octal.
    Thus gmp_init(010) becomes 8.

    $a=010; //8
    $b="010" + 0; //10
    $c=gmp_strval(gmp_init(010)); //8
    $d=gmp_strval(gmp_init("010")); //8

    This behaviour is inconsistent: either $d should equal $b, or
    $b should equal $a.
    up
    1
    Aurelien Marchand
    2 years ago
    Missing from the documentation: gmp_init() return false in case it failed to parse $num

    <?php
    var_dump    (gmp_init(""));
    // returns "bool(false)" and not a GMP object as hinted by the documentation, it also triggers a Warning "PHP Warning: gmp_init(): Unable to convert variable to GMP - string is not an integer in php shell code on line 1"

    ?>
    up
    -1
    charlie at oblivion dot cz
    17 years ago
    gmp_* functions don't accept strings with a leading '+':
    <?php
    echo gmp_strval(gmp_init('+42')); #0
    echo gmp_strval(gmp_add('42', '+42')); #42
    echo bcadd('+42', '+42'); #84
    ?>
    up
    -2
    thomas dot hebinck at digionline dot de
    19 years ago
    If you call a gmp_* function directly with an interger as parameter, this integer MUST NOT be 0:

    for($i=-1;$i<=1;$i++) { echo gmp_strval(gmp_add(2,gmp_mul(1,$i))) . ' '; }

    The result is 1 0 3 (wrong)

    In this case you have to use gmp_init():

    for($i=-1;$i<=1;$i++) { echo gmp_strval(gmp_add(2,gmp_mul(1,gmp_init($i)))) . ' '; }

    The result is 1 2 3 (right)

    Happy number crunching! :-)
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