PROCEDURE SHELLSORT(VAR SORTBUF : KEYARRAY; RECS : INTEGER);

VAR I,J,K,L : INTEGER;
    SPREAD  : INTEGER;


PROCEDURE INT_SWAP(VAR RR,SS : KEYREC);

VAR T : KEYREC;

BEGIN
  T := RR;
  RR := SS;
  SS := T
END;


BEGIN
  SPREAD := RECS DIV 2;       { First spread is half record count  }
  WHILE SPREAD > 0 DO         { Do until spread goes to zero:      }
    BEGIN
      FOR I := SPREAD + 1 TO RECS DO
        BEGIN
          J := I - SPREAD;
          WHILE J > 0 DO
            BEGIN             { Test & swap across the array }
              L := J + SPREAD;
              IF SORTBUF[J].KEY <= SORTBUF[L].KEY THEN J := 0 ELSE
                INT_SWAP(SORTBUF[J],SORTBUF[L]);
              J := J - SPREAD
            END
        END;
      SPREAD := SPREAD DIV 2    { Halve spread for next pass }
    END
END;