Arbitrary Precision

arbpre.js

/*
Use:
new ArbPre("123456781234780123487234").mulS(1000);
new ArbPre("123456781234780123487234").mul(new ArbPre("6289304527348952893045206"))
*/
class ArbPre {
    constructor(input) {
        if (typeof input === "number") {
            let nums = this._nums = [];
            while (input > 0) {
                nums.push(input % 10);
                input = Math.floor(input / 10);
            }
        }
        else if (typeof input === "string") {
            let nums = this._nums = input.split('').map(i => +i);
            nums.reverse();
            this._trimZero();
        }
        else {
            this._nums = [];
        }
    }
    _trimZero() {
        while (this._nums[this.length - 1] === 0 && this.length > 1) {
            this._nums.pop();
        }
    }
    
    get length() {
        return this._nums.length;
    }
    at(index) {
        return this._nums[index];
    }
    atAsString(index) {
        return this._nums[this._nums.length - 1 - index]
    }
    toString() {
        let result = '';
        for (let strNum of this._nums) {
            result = strNum + result;
        }
        return result;
    }
    clone() {
        let arbPre = new ArbPre;
        arbPre._nums = this._nums.slice();
        return arbPre;
    }
    sliceAsString(start, end) {
        start = (start == null || start === 0) ? this.length : -start;
        end = end === null ? 0 : -end;
        this._nums = this._nums.slice(end, start);
        return this;
    }
    slice(start, end) {
        this._nums = this._nums.slice(start, end);
        return this;
    }
    _addUnnorm(input) {
        let thisNums = this._nums;
        let inputNums = input._nums;
        
        let length = Math.max(thisNums.length, inputNums.length);
        
        for (let i = 0; i < length; i++) {
            thisNums[i] = (thisNums[i] || 0) + (inputNums[i] || 0);
        }
        return this;
    }
    _normalize() {
        let nums = this._nums;
        for (let i = 0; i < this.length; i++) {
            let num = nums[i];
            if (num >= 10) {
                nums[i + 1] = (nums[i + 1] || 0) + Math.floor(num / 10);
                nums[i] = num % 10;
            }
        }
        this._trimZero();
    }
    add(arbPre) {
        this._addUnnorm(arbPre);
        this._normalize();
        return this;
    }
    
    mul10(repeat) {
        for (let i = 0; i < repeat; i++) {
            this._nums.unshift(0);
        }
        return this;
    }
    
    mulS(inputNum) {
        for (let i = 0; i < this.length; i++) {
            this._nums[i] *= inputNum;
        }
        this._normalize();
        return this;
    }
    mul(arbPre) {
        let longerA;
        let shorter;
        if (this.length > arbPre.length) {
            longerA = this._nums;
            shorter = arbPre;
        }
        else {
            longerA = arbPre._nums;
            shorter = this;
        }
        
        let result = new ArbPre();
        for (let i = 0; i < longerA.length; i++) {
            let mul = shorter.clone().mulS(longerA[i]).mul10(i);
            result._addUnnorm(mul);
        }
        result._normalize();
        this._nums = result._nums;
        return result;
    }
}