Big Decimal

big-decimal.ts

export type BigDecimalCoersable = BigDecimal | string | number | bigint | undefined;

export class BigDecimal {

    // Configuration: constants
    public static decimalPrecision = 8; // number of decimals on all instances

    public static isRounded = true; // numbers are truncated (false) or rounded (true)

    protected static shift = BigInt('1' + '0'.repeat(BigDecimal.decimalPrecision)); // derived constant

    protected static fromBigInt(value: bigint) {
        const result = new BigDecimal();
        result.nValue = value;

        return result;
    }

    protected static divRound(dividend: bigint, divisor: bigint) {
        const two = BigInt(2);
        const zero = BigInt(0);
        const roundingValue = BigDecimal.isRounded ? dividend * two / divisor % two : zero;

        return BigDecimal.fromBigInt(dividend / divisor + roundingValue);
    }

    protected nValue: bigint;

    constructor(value: BigDecimalCoersable = undefined) {
        if (!value) {
            this.nValue = BigInt(0);
            return;
        }

        if (value instanceof BigDecimal) {
            this.nValue = value.nValue;
            return;
        }

        const [ints, decis] = String(value).split('.').concat('');

        this.nValue = BigInt(ints + decis.padEnd(BigDecimal.decimalPrecision, '0')
            .slice(0, BigDecimal.decimalPrecision))
            + BigInt(BigDecimal.isRounded && decis[BigDecimal.decimalPrecision] >= '5');
    }

    add(num: BigDecimalCoersable) {
        return BigDecimal.fromBigInt(this.nValue + new BigDecimal(num).nValue);
    }

    subtract(num: BigDecimalCoersable) {
        return BigDecimal.fromBigInt(this.nValue - new BigDecimal(num).nValue);
    }

    multiply(num: BigDecimalCoersable) {
        return BigDecimal.divRound(this.nValue * new BigDecimal(num).nValue, BigDecimal.shift);
    }

    divide(num: BigDecimalCoersable) {
        return BigDecimal.divRound(this.nValue * BigDecimal.shift, new BigDecimal(num).nValue);
    }

    toString() {
        const s = this.nValue.toString().padStart(BigDecimal.decimalPrecision + 1, '0');
        const ints = s.slice(0, -BigDecimal.decimalPrecision);
        const decis =  s.slice(-BigDecimal.decimalPrecision);

        return `${ints}.${decis}`.replace(/\.?0+$/, '');
    }
}