utils.js

//
// Utility functions.
//
// Copyright (c) 2016 Samuel Groß
//

// Return the hexadecimal representation of the given byte.
function hex(b) {
    return ('0' + b.toString(16)).substr(-2);
}

// Return the hexadecimal representation of the given byte array.
function hexlify(bytes) {
    var res = [];
    for (var i = 0; i < bytes.length; i++)
        res.push(hex(bytes[i]));

    return res.join('');
}

// Return the binary data represented by the given hexdecimal string.
function unhexlify(hexstr) {
    if (hexstr.length % 2 == 1)
        throw new TypeError("Invalid hex string");

    var bytes = new Uint8Array(hexstr.length / 2);
    for (var i = 0; i < hexstr.length; i += 2)
        bytes[i/2] = parseInt(hexstr.substr(i, 2), 16);

    return bytes;
}

function hexdump(data) {
    if (typeof data.BYTES_PER_ELEMENT !== 'undefined')
        data = Array.from(data);

    var lines = [];
    for (var i = 0; i < data.length; i += 16) {
        var chunk = data.slice(i, i+16);
        var parts = chunk.map(hex);
        if (parts.length > 8)
            parts.splice(8, 0, ' ');
        lines.push(parts.join(' '));
    }

    return lines.join('\n');
}

// Simplified version of the similarly named python module.
var Struct = (function() {
    // Allocate these once to avoid unecessary heap allocations during pack/unpack operations.
    var buffer      = new ArrayBuffer(8);
    var byteView    = new Uint8Array(buffer);
    var uint32View  = new Uint32Array(buffer);
    var float64View = new Float64Array(buffer);

    return {
        pack: function(type, value) {
            var view = type;        // See below
            view[0] = value;
            return new Uint8Array(buffer, 0, type.BYTES_PER_ELEMENT);
        },

        unpack: function(type, bytes) {
            if (bytes.length !== type.BYTES_PER_ELEMENT)
                throw Error("Invalid bytearray");

            var view = type;        // See below
            byteView.set(bytes);
            return view[0];
        },

        // Available types.
        int8:    byteView,
        int32:   uint32View,
        float64: float64View
    };
})();