#define CMP( callback, aa, bb ) \
( ( GvSV( a ) = ( aa ) ), ( GvSV( b ) = ( bb ) ), CmpAB( callback ) )

int CmpAB( SV* cmp ) {
    int rv;
	dSP;

    PUSHMARK(SP);

    if( call_sv( cmp, G_SCALAR|G_NOARGS ) != 1 )
        croak( "Bad comparator" );
    SPAGAIN;

    rv = POPi;

    PUTBACK; 
    return rv;
}

void topNbsAB( int n, SV *cmp, AV*data ) {
    SV* *topN;
    int len = av_len( data );
    int i, k;
    int left, right;
    SV* a = gv_fetchpv( "main::a", TRUE, SVt_PV );
    SV* b = gv_fetchpv( "main::b", TRUE, SVt_PV );
    Inline_Stack_Vars;
    Newz( 1, topN, n + 1, SV* );

    for( i = 0; i < n+1; i++ ) {
       topN[ i ] = newSViv( 0 );
    }

    for( i = 0; i <= len; i++ ) {
        SV *val = *av_fetch( data, i, 0 );
        if( CMP( cmp, val, topN[ n - 1] ) < 0 ) continue;

        left = 0;
        right = n - 1;
        while (left < right) {
           int middle = ( left + right ) >> 1;
           if( CMP( cmp, val, topN[ middle ] ) <= 0 ) {
              left = middle + 1;
           } else {
              right = middle;
           }
        }
		for( k = n; k > left; k-- ) topN[ k ] = topN[ k-1 ];
		topN[ left ] = val;
    }

    Inline_Stack_Reset;
    for( i = 0; i < n; i++ )
        Inline_Stack_Push( sv_2mortal( newSVsv( topN[ i ] ) ) );
    Safefree( topN );
    Inline_Stack_Done;
}