irec = interval recordDefine 4 sectors in each frame, they are basically double linked lists._cur_( current sector )        : irec's timestamps are bounded by                                  the frame's 2 time limits. - frame's starttime <= irec's starttime <= irec's endtime <= frame's endtime   --------------------------------------------------------------------------_inc_( incoming sector )       : irec's starttime is earlier than                                  the frame's startime. - irec's starttime < frame's starttime <= irec's endtime <= frame's endtime                      ------------------------------------------------------_pas_( passing through sector ): irec's timestamps are outside the                                 frame's 2 time limits. - irec's starttime < frame's starttime <= frame's endtime < irec's endtime                      ------------------------------------_out_( outgoing sector )       : irec's endtime is later than the                                 frame's endtime. - frame's starttime <= irec's starttime <= frame's endtime < irec's endtime   --------------------------------------------------------Under this construction,    current frame's _out_ may NOT be equal to next frame's _inc_    'cause some of irec in current frame's _out_ may be in next frame _pas_    and    some of irec in current frame's _pas_ may be in next frame _inc_Assumption: Each input irec given to SLOG API has at least part of its duration overlapped with the duration of the frame where the irec is located.  i.e.  There will be no irec whose starttime and endtime are totally out of the time range of the frame where the irec sits.Limitation: Since this algorithm does NOT move the irec across differentframes.  This is the reason that we have the assumption mentioned above.Create an extra sector, internal data structure, called _tmp_ sector.1st Pass( Forward in time ):    initialize _cur_, _inc_, _pas_, _out_, _tmp_ to Empty sectors.    for every irec given to SLOG API, do        store it in current frame's _cur_        if the frame is filled up,            set the frame's endtime   = last irec's endtime.            if this is the 1st frame                set the frame's starttime = earliest irec's starttime                ( 1st frame's starttime may need to be reset in the 2nd Pass )            else                set the frame's starttime = previous frame's endtime            endif            for all irec in _tmp_( i.e. previous frame's _pas_ & _out_ ), do                ( for the 1st frame, this does nothing, 'cause _tmp_ is empty )                distribute irec in _tmp_ into _inc_ and _pas_                if ( irec's endtime <= frame's endtime )                    move irec from _tmp_ to _inc_                else                    move irec from _tmp_ to _pas_                endif            enddo            for all irec in _cur_, do                if ( irec's endtime <= frame's endtime )                    if ( irec's starttime < frame's starttime )                        move irec to _inc_                    endif                    leave irec in _cur_                else                    if ( irec's starttime < frame's starttime )                        move irec to _pas_                    else                        move irec to _out_                    endif                endif                ( for the 1st frame, _inc_ & _pas_ should be empty )            enddo            if ( _tmp_ is NOT empty ) error            copy _pas_ & _out_ to next frame's _tmp_            dump the current frame content to the disk            ( for the 1st frame, only _cur_ & _out_ are non-empty )            cleanup _cur_, _inc_, _pas_, _out_.        endif    enddo    for last frame in the logfile( done by SLOG_CloseOutputStream() )    Set frame's endtime = latest endtime of all irec in _tmp_ & _cur_.    move all irec in _tmp_ to _inc_    ( for the last frame, there are only non-empty _inc_ and _cur_ sectors).2nd Pass( Backward in time ):    initialize _cur_, _inc_, _pas_, _out_, _tmp_ to Empty sectors.    for each frame retrieved starting from the end of the logfile, do        fill up _cur_, _inc_, _pas_, _out_ as it was stored in the logfile.        if ( this is the 1st frame )            set the frame's starttime = earliest irec's starttime                                        of all in _tmp_, _out_, _inc_        endif        for irec in _tmp_( i.e. next frame's _pas_ & _inc_ ), do            ( for the 1st end frame, _tmp_ is empty, this does nothing )            if ( irec's starttime >= current frame's starttime )                if ( irec is NOT in _out_ )                    move irec from _tmp_ to _out_                else                    rm irec from _tmp_                endif            else                if ( irec is NOT in _pas_ )                    move irec from _tmp_ to _pas_                else                    rm irec from _tmp_                endif            endif        enddo        if ( _tmp_ is NOT empty ) error        copy _pas_ & _inc_ to next frame's _tmp_        cleanup _cur_, _inc_, _pas_, _out_.    enddo