set99.F

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      SUBROUTINE set99(TRIGS,IFAX,N)
      REAL             TRIGS(n)
      INTEGER IFAX(*),JFAX(10),NLFAX(7)
C
C     SUBROUTINE 'SET99' - COMPUTES FACTORS OF N & TRIGONOMETRIC
C     FUNCTIONS REQUIRED BY FFT99 & FFT991
C
      SAVE nlfax
C
      DATA nlfax/6,8,5,4,3,2,1/
C
      ixxx=1
C
      del=4.0e0*asin(1.0e0)/float(n)
      nil=0
      nhl=(n/2)-1
      DO 10 k=nil,nhl
      angle=float(k)*del
      trigs(2*k+1)=cos(angle)
      trigs(2*k+2)=sin(angle)
   10 CONTINUE
C
C     FIND FACTORS OF N (8,6,5,4,3,2; ONLY ONE 8 ALLOWED)
C     LOOK FOR SIXES FIRST, STORE FACTORS IN DESCENDING ORDER
      nu=n
      ifac=6
      k=0
      il=1
   20 CONTINUE
      IF (mod(nu,ifac).NE.0) GO TO 30
      k=k+1
      jfax(k)=ifac
      IF (ifac.NE.8) GO TO 25
      IF (k.EQ.1) GO TO 25
      jfax(1)=8
      jfax(k)=6
   25 CONTINUE
      nu=nu/ifac
      IF (nu.EQ.1) GO TO 50
      IF (ifac.NE.8) GO TO 20
   30 CONTINUE
      il=il+1
      ifac=nlfax(il)
      IF (ifac.GT.1) GO TO 20
C
      WRITE(6,40) n
   40 FORMAT(4h1n =,i4,27h - CONTAINS illegal factors)
      RETURN
C
C     NOW REVERSE ORDER OF FACTORS
   50 CONTINUE
      nfax=k
      ifax(1)=nfax
      DO 60 i=1,nfax
      ifax(nfax+2-i)=jfax(i)
   60 CONTINUE
      ifax(10)=n
      RETURN
      END