tsvm/assets/disk0/tvdos/include/js-mp3/bits.js

var Bits = {
    createNew: function (vec) {
        var bits = {
            vec: vec, // ArrayBuffer
            bitPos: 0,
            bytePos: 0
        };

        /**
         * @return {number}
         */
        bits.Bit = function () {
            if (bits.vec.byteLength <= bits.bytePos) {
                // TODO: Should this return error?
                return 0;
            }
            var dv = new DataView(bits.vec, bits.bytePos);
            var tmp = (dv.getUint8(0) >>> (7 - bits.bitPos)) >>> 0;
            tmp &= 0x01;
            bits.bytePos += ((bits.bitPos + 1) >>> 3) >>> 0;
            bits.bitPos = (bits.bitPos + 1) & 0x07;
            return tmp;
        };

        /**
         * @return {number}
         */
        bits.Bits = function (num) {
            if (num === 0) {
                return 0;
            }
            if (bits.vec.byteLength <= bits.bytePos) {
                // TODO: Should this return error?
                return 0;
            }
            var bb = new DataView(bits.vec, bits.bytePos);
            // always end bit wise ops with >>> 0 so the result gets interpreted as unsigned.
            // don't use >>. If the left-most bit is 1 it will try to preseve the sign and thus will introduce 1's to the left. Always use >>>.
            // see https://stackoverflow.com/a/6798829
            var tmp = (((getValue(bb, 0) << 24) >>> 0) | ((getValue(bb, 1) << 16) >>> 0) | ((getValue(bb, 2) << 8) >>> 0) | (getValue(bb, 3) >>> 0)) >>> 0;
            tmp = (tmp << bits.bitPos) >>> 0;
            tmp = (tmp >>> (32 - num)) >>> 0;
            bits.bytePos += ((bits.bitPos + num) >>> 3) >>> 0;
            bits.bitPos = (bits.bitPos + num) & 0x07;
            return tmp;
        };

        bits.Tail = function (offset) {
            var a = new Uint8Array(bits.vec);
            return a.slice(bits.vec.byteLength - offset).buffer;
            // return new Uint8Array(bits.vec, bits.vec.byteLength - offset).buffer;
        };

        bits.LenInBytes = function () {
            return bits.vec.byteLength;
        };

        /**
         * @return {number}
         */
        bits.BitPos = function () {
            return ((bits.bytePos << 3) >>> 0) + bits.bitPos;
        };

        bits.SetPos = function (pos) {
            bits.bytePos = (pos >>> 3) >>> 0;
            bits.bitPos = (pos & 0x7) >>> 0;
        };

        return bits;
    },
    append: function (bits, buf) {
        return Bits.createNew(bits.vec.concat(buf));
    },
};

var getValue = function (dv, index) {
    if (index >= dv.byteLength) {
        return 0;
    }
    return dv.getUint8(index);
};

exports = Bits;