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C Copyright 1981-2007 ECMWF
C
C Licensed under the GNU Lesser General Public License which
C incorporates the terms and conditions of version 3 of the GNU
C General Public License.
C See LICENSE and gpl-3.0.txt for details.
C
SUBROUTINE FAX(IFAX,N,MODE)
DIMENSION IFAX(10)
COMMON /QQQQFFT/ IXXX
C
C MARK INITIALISATION AS 'OLD' TYPE
C
IXXX=0
C
NN=N
IF (IABS(MODE).EQ.1) GO TO 10
IF (IABS(MODE).EQ.8) GO TO 10
NN=N/2
IF ((NN+NN).EQ.N) GO TO 10
IFAX(1)=-99
RETURN
10 K=1
C TEST FOR FACTORS OF 4
20 IF (MOD(NN,4).NE.0) GO TO 30
K=K+1
IFAX(K)=4
NN=NN/4
IF (NN.EQ.1) GO TO 80
GO TO 20
C TEST FOR EXTRA FACTOR OF 2
30 IF (MOD(NN,2).NE.0) GO TO 40
K=K+1
IFAX(K)=2
NN=NN/2
IF (NN.EQ.1) GO TO 80
C TEST FOR FACTORS OF 3
40 IF (MOD(NN,3).NE.0) GO TO 50
K=K+1
IFAX(K)=3
NN=NN/3
IF (NN.EQ.1) GO TO 80
GO TO 40
C NOW FIND REMAINING FACTORS
50 L=5
INC=2
C INC ALTERNATELY TAKES ON VALUES 2 AND 4
60 IF (MOD(NN,L).NE.0) GO TO 70
K=K+1
IFAX(K)=L
NN=NN/L
IF (NN.EQ.1) GO TO 80
GO TO 60
70 L=L+INC
INC=6-INC
GO TO 60
80 IFAX(1)=K-1
C IFAX(1) CONTAINS NUMBER OF FACTORS
C IFAX(1) CONTAINS NUMBER OF FACTORS
NFAX=IFAX(1)
C SORT FACTORS INTO ASCENDING ORDER
IF (NFAX.EQ.1) GO TO 110
DO 100 II=2,NFAX
ISTOP=NFAX+2-II
DO 90 I=2,ISTOP
IF (IFAX(I+1).GE.IFAX(I)) GO TO 90
ITEM=IFAX(I)
IFAX(I)=IFAX(I+1)
IFAX(I+1)=ITEM
90 CONTINUE
100 CONTINUE
110 CONTINUE
IFAX(10)=0
RETURN
END
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