BCMath 任意精度数学

简介

对于任意精度的数学，如果有足够多的内存，PHP 提供的 BCMath 支持用字符串的形式表示任意大小和精度的数字，最大尺寸为 2147483647（即 0x7FFFFFFF）。

有效（即格式良好）的 BCMath 数字是匹配正则表达式 /^[+-]?[0-9]*(\.[0-9]*)?$/ 的字符串。

警告

BCMath 函数想要操作的是 string，如果传入了 float 可能无法达到想要的效果，因为 PHP 会将 float 的值转换为 string。也就意味着 string 可能会带科学计数法符号（BCMath 并不支持），另外在 PHP 8.0.0 之前，小数点分隔符也不支持本地化（BCMath 只能识别英文句号小数点）。

<?php
$num1 = 0; // (string) 0 => '0'
$num2 = -0.000005; // (string) -0.000005 => '-5.05E-6'
echo bcadd($num1, $num2, 6); // => '0.000000'

setlocale(LC_NUMERIC, 'de_DE'); // 使用逗号小数点
$num2 = 1.2; // (string) 1.2 => '1,2'
echo bcsub($num1, $num2, 1); // => '0.0'
?>

安装/配置
- 安装
- 运行时配置
BC 数学函数
- bcadd — 两个任意精度数字的加法计算
- bcceil — Round up arbitrary precision number
- bccomp — 比较两个任意精度的数字
- bcdiv — 两个任意精度的数字除法计算
- bcdivmod — Get the quotient and modulus of an arbitrary precision number
- bcfloor — Round down arbitrary precision number
- bcmod — 任意精度数字取模
- bcmul — 两个任意精度数字乘法计算
- bcpow — 任意精度数字的乘方
- bcpowmod — Raise an arbitrary precision number to another, reduced by a specified modulus
- bcround — Round arbitrary precision number
- bcscale — 设置/获取所有 bc math 函数的默认小数点保留位数
- bcsqrt — 任意精度数字的二次方根
- bcsub — 两个任意精度数字的减法
BcMath\Number — The BcMath\Number class
- BcMath\Number::add — Adds an arbitrary precision number
- BcMath\Number::ceil — Rounds up an arbitrary precision number
- BcMath\Number::compare — Compares two arbitrary precision numbers
- BcMath\Number::__construct — Creates a BcMath\Number object
- BcMath\Number::div — Divides by an arbitrary precision number
- BcMath\Number::divmod — Gets the quotient and modulus of an arbitrary precision number
- BcMath\Number::floor — Rounds down an arbitrary precision number
- BcMath\Number::mod — Gets the modulus of an arbitrary precision number
- BcMath\Number::mul — Multiplies an arbitrary precision number
- BcMath\Number::pow — Raises an arbitrary precision number
- BcMath\Number::powmod — Raises an arbitrary precision number, reduced by a specified modulus
- BcMath\Number::round — Rounds an arbitrary precision number
- BcMath\Number::__serialize — Serializes a BcMath\Number object
- BcMath\Number::sqrt — Gets the square root of an arbitrary precision number
- BcMath\Number::sub — Subtracts an arbitrary precision number
- BcMath\Number::__toString — Converts BcMath\Number to string
- BcMath\Number::__unserialize — Deserializes a data parameter into a BcMath\Number object

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＋添加备注

用户贡献的备注 3 notes

down

Hayley Watson ¶

10 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.

down

volek at adamv dot cz ¶

11 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;
}
?>

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ClaudiuS ¶

13 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
?>