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PHP - Manual: BC Math

2024-11-13

BCMath 任意精度数学

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User Contributed Notes 6 notes

up
56
Hayley Watson
6 years ago
This extension is an interface to the GNU implementation as a library of the Basic Calculator utility by Philip Nelson; hence the name.
up
21
volek at adamv dot cz
7 years ago
Note that when you use implementation of factorial that ClaudiuS made, you get results even if you try to calculate factorial of number that you normally can't, e.g. 2.5, -2, etc. Here is safer implementation:
<?php
/**
* Calculates a factorial of given number.
* @param string|int $num
* @throws InvalidArgumentException
* @return string
*/
function bcfact($num)
{
    if (!filter_var($num, FILTER_VALIDATE_INT) || $num <= 0) {
        throw new InvalidArgumentException(sprintf('Argument must be natural number, "%s" given.', $num));
    }

    for ($result = '1'; $num > 0; $num--) {
        $result = bcmul($result, $num);
    }

    return $result;
}
?>
up
18
ClaudiuS
9 years ago
Needed to compute some permutations and found the BC extension great but poor on functions, so untill this gets implemented here's the factorial function:

<?php
/* BC FACTORIAL
* n! = n * (n-1) * (n-2) .. 1 [eg. 5! = 5 * 4 * 3 * 2 * 1 = 120]
*/
function bcfact($n){
    $factorial=$n;
    while (--$n>1) $factorial=bcmul($factorial,$n);
    return $factorial;
}

print bcfact(50);
//30414093201713378043612608166064768844377641568960512000000000000
?>
up
-12
Artur Kuritsyn
4 years ago
Useful function for bcround

    function getBcRound($number, $precision = 0)
    {
        $precision = ($precision < 0)
                   ? 0
                   : (int) $precision;
        if (strcmp(bcadd($number, '0', $precision), bcadd($number, '0', $precision+1)) == 0) {
            return bcadd($number, '0', $precision);
        }
        if (getBcPresion($number) - $precision > 1) {
            $number = getBcRound($number, $precision + 1);
        }
        $t = '0.' . str_repeat('0', $precision) . '5';
        return $number < 0
               ? bcsub($number, $t, $precision)
               : bcadd($number, $t, $precision);
    }
   
    function getBcPresion($number) {
        $dotPosition = strpos($number, '.');
        if ($dotPosition === false) {
            return 0;
        }
        return strlen($number) - strpos($number, '.') - 1;
    }
   
    var_dump(getBcRound('3', 0) == number_format('3', 0));
    var_dump(getBcRound('3.4', 0) == number_format('3.4', 0));
    var_dump(getBcRound('3.56', 0) == number_format('3.6', 0));
    var_dump(getBcRound('1.95583', 2) == number_format('1.95583', 2));
    var_dump(getBcRound('5.045', 2) == number_format('5.045', 2));
    var_dump(getBcRound('5.055', 2) == number_format('5.055', 2));
    var_dump(getBcRound('9.999', 2) == number_format('9.999', 2));
    var_dump(getBcRound('5.0445', 5) == number_format('5.044500', 5));
    var_dump(getBcRound('5.0445', 4) == number_format('5.04450', 4));
    var_dump(getBcRound('5.0445', 3) == number_format('5.0445', 3));
    var_dump(getBcRound('5.0445', 2) == number_format('5.045', 2));
    var_dump(getBcRound('5.0445', 1) == number_format('5.05', 1));
    var_dump(getBcRound('5.0445', 0) == number_format('5.0', 0));//
    var_dump(getBcRound('5.04455', 2) == number_format('5.045', 2));
    var_dump(getBcRound('99.999', 2) == number_format('100.000', 2));
    var_dump(getBcRound('99.999') == number_format('99.999', 0));
    var_dump(getBcRound('99.999', 'a') == number_format('99.999', 0));
    var_dump(getBcRound('99.999', -1.5) == number_format('99.999', 0));
    var_dump(getBcRound('-0.00001', 2) == number_format('-0.000', 2));
    var_dump(getBcRound('-0.0000', 2) == number_format('0', 2));
    var_dump(getBcRound('-4.44455', 2) == number_format('-4.445', 2));
    var_dump(getBcRound('-4.44555', 0) == number_format('-4.5', 0));
    var_dump(getBcRound('-4.444444444444444444444444444444444444444444445', 0) == number_format('-4.5', 0));
up
-21
George Lund
8 years ago
It's worth noting that this library is named very wrongly.

It may be called 'Binary Calculator', but what you're getting is a decimal calculator that can represent base-10 fractions accurately.
up
-14
Anonymous
4 years ago
Useful function for bcround

    function getBcRound($number, $precision = 0)
    {
        $precision = ($precision < 0)
                   ? 0
                   : (int) $precision;
        if (strcmp(bcadd($number, '0', $precision), bcadd($number, '0', $precision+1)) == 0) {
            return bcadd($number, '0', $precision);
        }
        if (getBcPresion($number) - $precision > 1) {
            $number = getBcRound($number, $precision + 1);
        }
        $t = '0.' . str_repeat('0', $precision) . '5';
        return $number < 0
               ? bcsub($number, $t, $precision)
               : bcadd($number, $t, $precision);
    }
   
    function getBcPresion($number) {
        $dotPosition = strpos($number, '.');
        if ($dotPosition === false) {
            return 0;
        }
        return strlen($number) - strpos($number, '.') - 1;
    }
   
    var_dump(getBcRound('3', 0) == number_format('3', 0));
    var_dump(getBcRound('3.4', 0) == number_format('3.4', 0));
    var_dump(getBcRound('3.56', 0) == number_format('3.6', 0));
    var_dump(getBcRound('1.95583', 2) == number_format('1.95583', 2));
    var_dump(getBcRound('5.045', 2) == number_format('5.045', 2));
    var_dump(getBcRound('5.055', 2) == number_format('5.055', 2));
    var_dump(getBcRound('9.999', 2) == number_format('9.999', 2));
    var_dump(getBcRound('5.0445', 5) == number_format('5.044500', 5));
    var_dump(getBcRound('5.0445', 4) == number_format('5.04450', 4));
    var_dump(getBcRound('5.0445', 3) == number_format('5.0445', 3));
    var_dump(getBcRound('5.0445', 2) == number_format('5.045', 2));
    var_dump(getBcRound('5.0445', 1) == number_format('5.05', 1));
    var_dump(getBcRound('5.0445', 0) == number_format('5.0', 0));//
    var_dump(getBcRound('5.04455', 2) == number_format('5.045', 2));
    var_dump(getBcRound('99.999', 2) == number_format('100.000', 2));
    var_dump(getBcRound('99.999') == number_format('99.999', 0));
    var_dump(getBcRound('99.999', 'a') == number_format('99.999', 0));
    var_dump(getBcRound('99.999', -1.5) == number_format('99.999', 0));
    var_dump(getBcRound('-0.00001', 2) == number_format('-0.000', 2));
    var_dump(getBcRound('-0.0000', 2) == number_format('0', 2));
    var_dump(getBcRound('-4.44455', 2) == number_format('-4.445', 2));
    var_dump(getBcRound('-4.44555', 0) == number_format('-4.5', 0));
    var_dump(getBcRound('-4.444444444444444444444444444444444444444444445', 0) == number_format('-4.5', 0));
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官方地址：https://www.php.net/manual/en/book.bc.php

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