longbits.js

"use strict";

module.exports = LongBits;

var util = require("../util");

/**
 * Constructs new long bits.
 * @classdesc Helper class for working with the low and high bits of a 64 bit value.
 * @memberof util
 * @constructor
 * @param {number} lo Low bits
 * @param {number} hi High bits
 */
function LongBits(lo, hi) { // make sure to always call this with unsigned 32bits for proper optimization

    /**
     * Low bits.
     * @type {number}
     */
    this.lo = lo;

    /**
     * High bits.
     * @type {number}
     */
    this.hi = hi;
}

/** @alias util.LongBits.prototype */
var LongBitsPrototype = LongBits.prototype;

/**
 * Zero bits.
 * @memberof util.LongBits
 * @type {util.LongBits}
 */
var zero = new LongBits(0, 0);

zero.toNumber = function() { return 0; };
zero.zzEncode = zero.zzDecode = function() { return this; };
zero.length = function() { return 1; };

/**
 * Constructs new long bits from the specified number.
 * @param {number} value Value
 * @returns {util.LongBits} Instance
 */
LongBits.fromNumber = function fromNumber(value) {
    if (value === 0)
        return zero;
    var sign  = value < 0;
        value = Math.abs(value);
    var lo = value >>> 0,
        hi = (value - lo) / 4294967296 >>> 0;
    if (sign) {
        hi = ~hi >>> 0;
        lo = ~lo >>> 0;
        if (++lo > 4294967295) {
            lo = 0;
            if (++hi > 4294967295)
                hi = 0;
        }
    }
    return new LongBits(lo, hi);
};

/**
 * Constrcuts new long bits from a number or long.
 * @param {Long|number|string} value Value
 * @returns {util.LongBits} Instance
 */
LongBits.from = function from(value) {
    var type = typeof value, result=zero;
    if(type === 'number')
        result = LongBits.fromNumber(value);
    else 
    {
        if(type === 'string' && util.Long)
            value = util.Long.fromString(value);
    
        if(value.low || value.high)
            result = new LongBits(value.low >>> 0, value.high >>> 0);
    }
        
    return result;
};

/**
 * Converts this long bits to a possibly unsafe JavaScript number.
 * @param {boolean} [unsigned=false] Whether unsigned or not
 * @returns {number} Possibly unsafe number
 */
LongBitsPrototype.toNumber = function toNumber(unsigned) {
    if (!unsigned && this.hi >>> 31) {
        this.lo = ~this.lo + 1 >>> 0;
        this.hi = ~this.hi     >>> 0;
        if (!this.lo)
            this.hi = this.hi + 1 >>> 0;
        return -(this.lo + this.hi * 4294967296);
    }
    return this.lo + this.hi * 4294967296;
};

/**
 * Converts this long bits to a long.
 * @param {boolean} [unsigned=false] Whether unsigned or not
 * @returns {Long} Long
 */
LongBitsPrototype.toLong = function toLong(unsigned) {
    return new util.Long(this.lo, this.hi, unsigned);
};

var charCodeAt = String.prototype.charCodeAt;

/**
 * Constructs new long bits from the specified 8 characters long hash.
 * @param {string} hash Hash
 * @returns {util.LongBits} Bits
 */
LongBits.fromHash = function fromHash(hash) {
    return new LongBits(
        ( charCodeAt.call(hash, 0)
        | charCodeAt.call(hash, 1) << 8
        | charCodeAt.call(hash, 2) << 16
        | charCodeAt.call(hash, 3) << 24) >>> 0
    ,
        ( charCodeAt.call(hash, 4)
        | charCodeAt.call(hash, 5) << 8
        | charCodeAt.call(hash, 6) << 16
        | charCodeAt.call(hash, 7) << 24) >>> 0
    );
};

/**
 * Converts this long bits to a 8 characters long hash.
 * @returns {string} Hash
 */
LongBitsPrototype.toHash = function toHash() {
    return String.fromCharCode(
        this.lo        & 255,
        this.lo >>> 8  & 255,
        this.lo >>> 16 & 255,
        this.lo >>> 24 & 255,
        this.hi        & 255,
        this.hi >>> 8  & 255,
        this.hi >>> 16 & 255,
        this.hi >>> 24 & 255
    );
};

/**
 * Zig-zag encodes this long bits.
 * @returns {util.LongBits} `this`
 */
LongBitsPrototype.zzEncode = function zzEncode() {
    var mask =   this.hi >> 31;
    this.hi  = ((this.hi << 1 | this.lo >>> 31) ^ mask) >>> 0;
    this.lo  = ( this.lo << 1                   ^ mask) >>> 0;
    return this;
};

/**
 * Zig-zag decodes this long bits.
 * @returns {util.LongBits} `this`
 */
LongBitsPrototype.zzDecode = function zzDecode() {
    var mask = -(this.lo & 1);
    this.lo  = ((this.lo >>> 1 | this.hi << 31) ^ mask) >>> 0;
    this.hi  = ( this.hi >>> 1                  ^ mask) >>> 0;
    return this;
};

/**
 * Calculates the length of this longbits when encoded as a varint.
 * @returns {number} Length
 */
LongBitsPrototype.length = function length() {
    var part0 =  this.lo,
        part1 = (this.lo >>> 28 | this.hi << 4) >>> 0,
        part2 =  this.hi >>> 24;
    if (part2 === 0) {
        if (part1 === 0)
            return part0 < 1 << 14
                ? part0 < 1 << 7 ? 1 : 2
                : part0 < 1 << 21 ? 3 : 4;
        return part1 < 1 << 14
            ? part1 < 1 << 7 ? 5 : 6
            : part1 < 1 << 21 ? 7 : 8;
    }
    return part2 < 1 << 7 ? 9 : 10;
};