kvclient-js/lib/Hex2Dec.js

Oracle NoSQL Database node.js Client API.

/*
 * http://www.danvk.org/hex2dec.html
 * Apache 2 Licensed
 *
 * A function for converting hex <-> dec w/o loss of precision.
 *
 * The problem is that parseInt("0x12345...") isn't precise enough to convert
 * 64-bit integers correctly.
 *
 * Internally, this uses arrays to encode decimal digits starting with the least
 * significant:
 * 8 = [8]
 * 16 = [6, 1]
 * 1024 = [4, 2, 0, 1]
 *
 */

// Adds two arrays for the given base (10 or 16), returning the result.
// This turns out to be the only "primitive" operation we need.
function add(x, y, base) {
    var z = [];
    var n = Math.max(x.length, y.length);
    var carry = 0;
    var i = 0;
    while (i < n || carry) {
        var xi = i < x.length ? x[i] : 0;
        var yi = i < y.length ? y[i] : 0;
        var zi = carry + xi + yi;
        z.push(zi % base);
        carry = Math.floor(zi / base);
        i++;
    }
    return z;
}

// Returns a*x, where x is an array of decimal digits and a is an ordinary
// JavaScript number. base is the number base of the array x.
function multiplyByNumber(num, x, base) {
    if (num < 0) return null;
    if (num == 0) return [];

    var result = [];
    var power = x;
    while (true) {
        if (num & 1) {
            result = add(result, power, base);
        }
        num = num >> 1;
        if (num === 0) break;
        power = add(power, power, base);
    }

    return result;
}

function parseToDigitsArray(str, base) {
    var digits = str.split('');
    var ary = [];
    for (var i = digits.length - 1; i >= 0; i--) {
        var n = parseInt(digits[i], base);
        if (isNaN(n)) return null;
        ary.push(n);
    }
    return ary;
}

function convertBase(str, fromBase, toBase) {
    var digits = parseToDigitsArray(str, fromBase);
    if (digits === null) return null;

    var outArray = [];
    var power = [1];
    for (var i = 0; i < digits.length; i++) {
        // invariant: at this point, fromBase^i = power
        if (digits[i]) {
            outArray = add(outArray, multiplyByNumber(digits[i], power, toBase), toBase);
        }
        power = multiplyByNumber(fromBase, power, toBase);
    }

    var out = '';
    for (var i = outArray.length - 1; i >= 0; i--) {
        out += outArray[i].toString(toBase);
    }
    return out;
}

exports.decToHex = function (decStr) {
    var hex = convertBase(decStr, 10, 16);
    return hex ? '0x' + hex : null;
};

exports.hexToDec = function (hexStr) {
    if (hexStr.substring(0, 2) === '0x') hexStr = hexStr.substring(2);
    hexStr = hexStr.toLowerCase();
    return convertBase(hexStr, 16, 10);
};