source: flex_extract.git/Source/Fortran/set99.f90 @ 4f24798

!c Copyright 1981-2016 ECMWF.
!c
!c This software is licensed under the terms of the Apache Licence 
!c Version 2.0 which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
!c
!c In applying this licence, ECMWF does not waive the privileges and immunities 
!c granted to it by virtue of its status as an intergovernmental organisation 
!c nor does it submit to any jurisdiction.
!c

      SUBROUTINE SET99(TRIGS,IFAX,N)
      DIMENSION TRIGS(N),IFAX(*),JFAX(10),LFAX(7)
!C
!C     SUBROUTINE 'SET99' - COMPUTES FACTORS OF N & TRIGONOMETRIC
!C     FUNCTIONS REQUIRED BY FFT99 & FFT991
!C
      DATA LFAX/6,8,5,4,3,2,1/
      IXXX=1
!C
      DEL=4.0*ASIN(1.0)/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
      L=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
      L=L+1
      IFAC=LFAX(L)
      IF (IFAC.GT.1) GO TO 20
!C
      WRITE(6,40) N
   40 FORMAT('1N =',I4,' - 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