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SUBROUTINE DSINT1(N,WAR,WAS,XH,X,IFAC)
IMPLICIT DOUBLE PRECISION (A-H,O-Z)
DIMENSION WAR(*),WAS(*),X(*),XH(*),IFAC(*)
DATA SQRT3 /1.73205080756887729352D0/
DO 100 I=1,N
XH(I) = WAR(I)
WAR(I) = X(I)
100 CONTINUE
IF (N.lt.2) GO TO 101
IF (N.eq.2) GO TO 102
GO TO 103
101 XH(1) = XH(1)+XH(1)
GO TO 106
102 XHOLD = SQRT3*(XH(1)+XH(2))
XH(2) = SQRT3*(XH(1)-XH(2))
XH(1) = XHOLD
GO TO 106
103 NP1 = N+1
NS2 = N/2
X(1) = 0.0D0
DO 104 K=1,NS2
KC = NP1-K
T1 = XH(K)-XH(KC)
T2 = WAS(K)*(XH(K)+XH(KC))
X(K+1) = T1+T2
X(KC+1) = T2-T1
104 CONTINUE
MODN = MOD(N,2)
IF (MODN .NE. 0) X(NS2+2) = 4.0D0*XH(NS2+1)
CALL DFFTF1 (NP1,X,XH,WAR,IFAC)
XH(1) = 0.5D0*X(1)
DO 105 I=3,N,2
XH(I-1) = -X(I)
XH(I) = XH(I-2)+X(I-1)
105 CONTINUE
IF (MODN .NE. 0) GO TO 106
XH(N) = -X(N+1)
106 DO 107 I=1,N
X(I) = WAR(I)
WAR(I) = XH(I)
107 CONTINUE
RETURN
END
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