var File = MSDOS;
var X = MSDOS;

/**
 * Get the “base” offset, after the header.
 * @param {Int} [nOffset=0] - The offset from the base offset.
 * @returns {Int}
 */
MSDOS.getBaseOffset = function(nOffset) {
    if (arguments.length == 0) {
        nOffset = 0;
    }
    return (MSDOS.readWord(8) << 4) + nOffset;
}

/**
 * Translate segment/offset address pair to file offset.
 * @param {UShort} nSegment - Segment address.
 * @param {UShort} [nOffset=0] - Offset address.
 * @returns {Int}
 */
MSDOS.AddressToOffset = function(nSegment, nOffset) {
    if (arguments.length == 1) {
        nOffset = 0;
    }
    nOffset += nSegment << 4;
    return MSDOS.getBaseOffset(nOffset & 0xFFFFF);
}

/**
 * Get the entry point file offset.
 * @param {Int} [nOffset=0] - The offset from the entry point.
 * @returns {Int}
 */
MSDOS.getEntryPointOffset = function(nOffset) {
    if (arguments.length == 0) {
        nOffset = 0;
    }
    return MSDOS.AddressToOffset(MSDOS.readWord(0x16), MSDOS.readWord(0x14)) + nOffset;
}

/**
 * Get the NewExe (or LE/LX) file offset (assuming it's valid).
 * @param {Int} [nOffset=0] - The offset from the NewExe offset.
 * @returns {Int}
 */
MSDOS.getNEOffset = function(nOffset) {
    if (arguments.length == 0) {
        nOffset = 0;
    }
    return MSDOS.readDword(0x3C) + nOffset;
}