source: main/trunk/model-sites-dev/respooled/collect/popup-video-respooled/js/midi/inc/jasmid/stream.js@ 29863

/* Wrapper for accessing strings through sequential reads */
function Stream(str) {
    var position = 0;
    
    function read(length) {
        var result = str.substr(position, length);
        position += length;
        return result;
    }
    
    /* read a big-endian 32-bit integer */
    function readInt32() {
        var result = (
            (str.charCodeAt(position) << 24)
            + (str.charCodeAt(position + 1) << 16)
            + (str.charCodeAt(position + 2) << 8)
            + str.charCodeAt(position + 3));
        position += 4;
        return result;
    }

    /* read a big-endian 16-bit integer */
    function readInt16() {
        var result = (
            (str.charCodeAt(position) << 8)
            + str.charCodeAt(position + 1));
        position += 2;
        return result;
    }
    
    /* read an 8-bit integer */
    function readInt8(signed) {
        var result = str.charCodeAt(position);
        if (signed && result > 127) result -= 256;
        position += 1;
        return result;
    }
    
    function eof() {
        return position >= str.length;
    }
    
    /* read a MIDI-style variable-length integer
        (big-endian value in groups of 7 bits,
        with top bit set to signify that another byte follows)
    */
    function readVarInt() {
        var result = 0;
        while (true) {
            var b = readInt8();
            if (b & 0x80) {
                result += (b & 0x7f);
                result <<= 7;
            } else {
                /* b is the last byte */
                return result + b;
            }
        }
    }
    
    return {
        'eof': eof,
        'read': read,
        'readInt32': readInt32,
        'readInt16': readInt16,
        'readInt8': readInt8,
        'readVarInt': readVarInt
    }
}