JavaScript 对大整数求和

Question

在 JavaScript 中，我想使用以下方法创建大型布尔数组（54 个元素）的二进制哈希：

function bhash(arr) {
   for (var i = 0, L = arr.length, sum = 0; i < L; sum += Math.pow(2,i)*arr[i++]); 
   return sum;
}

简而言之：它创建了存储布尔数组的最小整数。现在我的问题是 javascript 显然使用 floats 作为默认值。我必须创建的最大数字是 2^54-1 但是一旦 javascript 达到 2^53 它就会开始做奇怪的事情：

9007199254740992+1 = 9007199254740994

有没有办法在javascript中使用整数而不是浮点数？还是大整数求和？

Answer 1

您可以通过谷歌搜索找到各种 BigInteger Javascript 库。例如http://www.leemon.com/crypto/BigInt.html

Answer 2

没有。 Javascript 只有一种数字类型。您必须自己编写代码或使用大型整数库（甚至不能重载算术运算符）。

更新

这在 2010 年是真的……现在（2019 年）BigInt 库正在标准化，很可能很快就会在 Javascript 中以原生方式出现，它将是第二个存在的数字类型（有类型化数组，但是 - 至少在形式上- 从它们中提取的值仍然是双精度浮点数）。

Answer 3

JavaScript 内部使用浮点数。

What is JavaScript's highest integer value that a number can go to without losing precision?

换句话说，您不能使用超过 53 位。在某些实现中，您可能会被限制为 31 个。

尝试将位存储在多个变量中，使用字符串，或获取bignum library，或者如果您只需要处理整数，则使用biginteger library。

Answer 4

您的系统可能遇到了字节长度限制。我将获取布尔数组，将其转换为二进制数字数组（[true, false, true] => [1,0,1]），然后将此数组加入字符串“101”，然后使用 parseInt ('101',2)，你就会得到答案。

Answer 5

这里是(yet another) wrapper around Leemon Baird's BigInt.js

在online demo of a big integer calculator in JavaScript 中使用了它，它实现了通常的四个操作 + - * /、模数 (%) 和四个内置函数：平方根 (sqrt)、幂 (pow)、递归阶乘 ( fact) 和一个记忆斐波那契 (fibo)。

Answer 6

www.javascripter.net/math/calculators/100digitbigintcalculator.htm 提供了大整数运算的另一种实现（也使用 BigInt.js）。支持操作 + - * / 以及余数、GCD、LCM、阶乘、素数测试、下一个素数、上一个素数。

Answer 7

javascript 现在有experimental support for BigInt。
在撰写本文时，只有 chrome 支持这一点。

caniuse还没有条目。

BigInt 可以与构造函数一起使用，例如BigInt(20) 或附加 n，例如20n

例子：

const max = Number.MAX_SAFE_INTEGER;

console.log('javascript Number limit reached', max + 1 === max + 2) // true;

console.log('javascript BigInt limit reached', BigInt(max) + 1n === BigInt(max) + 2n); // false

Answer 8

BigInt 被添加为 JavaScript 的原生功能。

typeof 123;
// → 'number'
typeof 123n;
// → 'bigint'

例子：

const max = BigInt(Number.MAX_SAFE_INTEGER);
const two = 2n;
const result = max + two;
console.log(result);
// → '9007199254740993'

Answer 9

因此，在尝试其中一个 leetcode 问题时，我编写了一个函数，它以字符串的形式接收两个数字，并以字符串的形式返回这些数字的总和。 （这不适用于负数，尽管我们可以修改此函数以覆盖它）

var addTwoStr = function (s1, s2) {
s1 = s1.split("").reverse().join("")
s2 = s2.split("").reverse().join("")
var carry = 0, rS = '', x = null
if (s1.length > s2.length) {
    for (let i = 0; i < s1.length; i++) {
        let s = s1[i]
        if (i < s2.length) {
            x = Number(s) + Number(s2[i]) + carry
            rS += String((x % 10))
            carry = parseInt(x/10)
        } else {
            if (carry) {
                x = Number(s) + carry
                rS += String((x % 10))
                carry = parseInt(x/10)
            } else {
                rS += s
            }
        }
    }
} else {
    for (let i = 0; i < s2.length; i++) {
        let s = s2[i]
        if (i < s1.length) {
            x = Number(s) + Number(s1[i]) + carry
            rS += String((x % 10))
            carry = parseInt(x/10)
        } else {
            if (carry) {
                x = Number(s) + carry
                rS += String((x % 10))
                carry = parseInt(x/10)
            } else {
                rS += s
            }
        }
    }
}
if (carry) {
    rS += String(carry)
}
return rS.split("").reverse().join("")
}

示例：addTwoStr('120354566', '321442535') 输出：“441797101”

Answer 10

/** --if you want to show a big int as your wish use install and require this module
 * By using 'big-integer' module is easier to use and handling the big int numbers than regular javascript
 * https://www.npmjs.com/package/big-integer
*/

let bigInt = require('big-integer');

//variable: get_bigInt
let get_bigInt = bigInt("999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999");

let arr = [1, 100000, 21, 30, 4, BigInt(999999999999), get_bigInt.value];

console.log(arr[6]); // Output: 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999n

//Calculation
console.log(arr[6] + 1n); // +1
console.log(arr[6] + 100n); // +100
console.log(arr[6] - 1n); // -1
console.log(arr[6] - 10245n); // -1000n

console.log((arr[6] * 10000n) + 145n - 435n);