CTITLEMGCOMD -- FIND GREATEST COMMON DIVISOR                            00000010
C***********************************************************************
C                 COPYRIGHT ATLANTIC RICHFIELD COMPANY 1991            *
C***********************************************************************
CA    AUTHOR       DANIEL POLAK                                         00000020
CA    DESIGNER     DANIEL POLAK                                         00000030
CA    LANGUAGE     FORTRAN H                                            00000040
CA    SYSTEM       S/370                                                00000050
CA    WRITTEN      01-13-81                                             00000060
C     REVISED      MO-DA-YR BY PROGRAMMER FOR REASON                    00000070
C     REVISED                                                           00000080
CA                                                                      00000090
CA    CALL MGCOMD (IND, NUM, IDIV)                                      00000100
CA                                                                      00000110
CA    IN/OUT ARGUMENT TYPE DESCRIPTION                                  00000120
CA                                                                      00000130
CA    IN     IND      I4   ARRAY TO FIND GREATEST COMMON DIVISOR        00000140
CA    IN     NUM      I4   NUMBER OF ELEMENTS IN IND                    00000150
CA    OUT    IDIV     I4   GREATEST COMMON DIVISOR                      00000160
CA                                                                      00000170
CA    MGCOMD FINDS THE GREATEST COMMON DIVISOR OF ELEMENTS OF THE       00000180
CA    IND ARRAY.                                                        00000190
C                                                                       00000200
      SUBROUTINE MGCOMD (IND, NUM, IDIV)                                00000210
C                                                                       00000220
C     INTEGER ARRAY IN PARAMETER LIST                                   00000230
C                                                                       00000240
      INTEGER      IND   (1)                                            00000250
C                                                                       00000260
C     FIND 2 DIFFERENT NUMBERS                                          00000270
C                                                                       00000280
      J = 1                                                             00000290
      NUM1 = IND(1)                                                     00000300
   10 J = J + 1                                                         00000310
      IF (J .GT. NUM) GO TO                                         40  00000320
      NUM2 = IND(J)                                                     00000330
      IF  (NUM2 .EQ. NUM1)  GO TO                                   10  00000340
C                                                                       00000350
C     DIFF = DIFFERENCE BETWEEN TWO NUMBERS                             00000360
C                                                                       00000370
      DIFF = IABS(NUM2 - NUM1)                                          00000380
C                                                                       00000390
C     FIND THE GREATEST COMMON DIVISOR                                  00000400
C                                                                       00000410
C     GREATEST COMMON DIVISOR MUST BE LESS THAN OR EQUAL TO DIFF        00000420
C     AND DIFF MUST BE A MULTIPLE OF THE GREATEST COMMON DIVISOR        00000430
C                                                                       00000440
      LM = DIFF - 1                                                     00000450
      IF  (LM .LE. 0)  GO TO                                        40  00000460
C                                                                       00000470
        DO 30 I = 1, LM                                                 00000480
        MM = DIFF / I                                                   00000490
        IF ((DIFF / MM) * MM .NE. DIFF)  GO TO                      30  00000500
        MA = MOD(NUM1, MM)                                              00000510
C                                                                       00000520
C     MM IS A DIVISOR OF DIFF.  IS IT THE GREATEST COMMON               00000530
C     DIVISOR OF ALL ARRAY ELEMENTS?                                    00000540
C                                                                       00000550
          DO 20 J = 1, NUM                                              00000560
          NUM2 = IND(J)                                                 00000570
          IF  (MA .NE. MOD(NUM2, MM))  GO TO                        30  00000580
   20     CONTINUE                                                      00000590
C                                                                       00000600
        GO TO                                                       50  00000610
C                                                                       00000620
   30   CONTINUE                                                        00000630
C                                                                       00000640
   40 IDIV = 1                                                          00000650
C                                                                       00000660
      GO TO                                                         60  00000670
C                                                                       00000680
   50 IDIV = MM                                                         00000690
C                                                                       00000700
   60 RETURN                                                            00000710
      END                                                               00000720