NAME
        Seek -- Set the current position for reading and writing

    SYNOPSIS
        oldPosition = Seek( file, position, mode )
        D0                  D1    D2        D3

        long seek(bptr, long, long)

    FUNCTION
        Seek() sets the read/write cursor for the file 'file' to the
        position 'position'. This position is used by both read() and
        write() as a place to start reading or writing. the result is the
        current absolute position in the file, or -1 if an error occurs, in
        which case ioerr() can be used to find more information. 'mode' can
        be OFFSET_BEGINNING, OFFSET_CURRENT or OFFSET_END. It is used to
        specify the relative start position. For example, 20 from current
        is a position 20 bytes forward from current, -20 is 20 bytes back
        from current.

        So that to find out where you are, seek zero from current. The end
        of the file is a Seek() positioned by zero from end. You cannot
        Seek() beyond the end of a file.

    INPUTS
        file - BCPL pointer to a file handle
        position - integer
        mode - integer

    RESULTS
        oldPosition - integer

    BUGS
        The V36 and V37 ROM filesystem (and V36/V37 l:fastfilesystem)
        returns the current position instead of -1 on an error.  It sets
        ioerr() to 0 on success, and an error code on an error.  this bug
        was fixed in the V39 filesystem.

    SEE ALSO
        read(), write(), setfilesize()