sigfig/utils/sigfig.js

Round a number to n significant figures.

/* eslint-disable complexity */
import { convertNumberToString, normalizeNumberString, } from '../utils/number.js';
function getFirstNonZeroDigitToRightIndex(num) {
    for (let i = num.indexOf('.') + 1; i < num.length; i += 1) {
        if (num[i] !== '0')
            return i;
    }
    return undefined;
}
export function sigfig(numberOrString, numSigfigs) {
    if (numSigfigs !== undefined &&
        (numSigfigs <= 0 || !Number.isInteger(numSigfigs))) {
        throw new TypeError('The number of significant figures to round to must be an integer greater than 0.');
    }
    const { normalizedNumberString: numberString, isNegative } = normalizeNumberString(convertNumberToString(numberOrString));
    // By this point, a number will always be represented either .xyz or xyz.
    const decimalIndex = numberString.indexOf('.');
    // Handle the case when there are only zeros in the number
    if (/^[0.]+$/.test(numberString)) {
        if (numSigfigs === undefined) {
            if (numberString === '.')
                return 1;
            else
                return numberString.length - 1;
        }
        else {
            if (numSigfigs === 1) {
                return '0';
            }
            else {
                return `0.${'0'.repeat(numSigfigs)}`;
            }
        }
    }
    const firstNonZeroDigitToRightIndex = getFirstNonZeroDigitToRightIndex(numberString);
    if (numSigfigs === undefined) {
        if (numberString.startsWith('.')) {
            return numberString.length - firstNonZeroDigitToRightIndex;
        }
        else {
            return numberString.length - 1;
        }
    }
    else {
        const roundedDecimal = roundDecimal(numberString, numSigfigs);
        const wholeNumberLength = decimalIndex;
        let answer = roundedDecimal.padEnd(Math.max(wholeNumberLength, roundedDecimal.includes('.') ? numSigfigs + 1 : numSigfigs), '0');
        // Normalizing the answer
        if (answer.startsWith('.')) {
            answer = '0' + answer;
        }
        if (answer.endsWith('.')) {
            answer = answer.slice(0, -1);
        }
        return isNegative ? `-${answer}` : answer;
    }
}
function roundDecimal(numberString, numSigfigs) {
    const digits = [];
    let roundingDigit;
    let firstNonZeroDigitIndex;
    let numSigfigsEncountered = 0;
    if (numberString.startsWith('.'))
        numberString = '0' + numberString;
    for (let i = 0; i < numberString.length; i += 1) {
        const digit = numberString[i];
        digits.push(digit);
        if (firstNonZeroDigitIndex === undefined &&
            digit !== '0' &&
            digit !== '.') {
            firstNonZeroDigitIndex = i;
        }
        if (firstNonZeroDigitIndex !== undefined && digit >= '0' && digit <= '9') {
            numSigfigsEncountered += 1;
            if (numSigfigsEncountered === numSigfigs) {
                roundingDigit =
                    (numberString[i + 1] === '.'
                        ? numberString[i + 2]
                        : numberString[i + 1]) ?? '0';
                break;
            }
        }
    }
    if (firstNonZeroDigitIndex === undefined) {
        throw new Error('firstNonZeroDigitIndex should not be undefined');
    }
    for (let i = numSigfigsEncountered; i < numSigfigs; i += 1) {
        digits.push('0');
    }
    if (roundingDigit === undefined || roundingDigit < '5') {
        return digits.join('');
    }
    let carry = false;
    for (let i = digits.length - 1; i >= 0; i -= 1) {
        const digit = digits[i];
        if (digit === '.') {
            continue;
        }
        if (digit === '9') {
            digits[i] = 0;
            carry = true;
        }
        else {
            if (i < firstNonZeroDigitIndex) {
                digits.pop();
            }
            digits[i] = String(Number(digit) + 1);
            carry = false;
            break;
        }
    }
    // The first digit is now a "0"
    if (carry) {
        digits.unshift('1');
    }
    if (digits.at(-1) === '.')
        digits.pop();
    return digits.join('');
}