share/fftpack5/fortran/costf1.f

   1 CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
   2 C
   3 C   FFTPACK 5.0
   4 C
   5 C   Authors:  Paul N. Swarztrauber and Richard A. Valent
   6 C
   7 C   $Id$
   8 C
   9 CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
  10
  11       SUBROUTINE COSTF1(N,INC,X,WSAVE,WORK,IER)
  12       REAL       X(INC,*)       ,WSAVE(*)
  13       DOUBLE PRECISION           DSUM
  14       IER = 0
  15       NM1 = N-1
  16       NP1 = N+1
  17       NS2 = N/2
  18       IF (N-2) 200,101,102
  19   101 X1H = X(1,1)+X(1,2)
  20       X(1,2) = .5*(X(1,1)-X(1,2))
  21       X(1,1) = .5*X1H
  22       GO TO 200
  23   102 IF (N .GT. 3) GO TO 103
  24       X1P3 = X(1,1)+X(1,3)
  25       TX2 = X(1,2)+X(1,2)
  26       X(1,2) = .5*(X(1,1)-X(1,3))
  27       X(1,1) = .25*(X1P3+TX2)
  28       X(1,3) = .25*(X1P3-TX2)
  29       GO TO 200
  30   103 DSUM = X(1,1)-X(1,N)
  31       X(1,1) = X(1,1)+X(1,N)
  32       DO 104 K=2,NS2
  33          KC = NP1-K
  34          T1 = X(1,K)+X(1,KC)
  35          T2 = X(1,K)-X(1,KC)
  36          DSUM = DSUM+WSAVE(KC)*T2
  37          T2 = WSAVE(K)*T2
  38          X(1,K) = T1-T2
  39          X(1,KC) = T1+T2
  40   104 CONTINUE
  41       MODN = MOD(N,2)
  42       IF (MODN .EQ. 0) GO TO 124
  43       X(1,NS2+1) = X(1,NS2+1)+X(1,NS2+1)
  44   124 LENX = INC*(NM1-1)  + 1
  45       LNSV = NM1 + INT(LOG(REAL(NM1))/LOG(2.)) + 4
  46       LNWK = NM1
  47 C
  48       CALL RFFT1F(NM1,INC,X,LENX,WSAVE(N+1),LNSV,WORK,
  49      1            LNWK,IER1)
  50       IF (IER1 .NE. 0) THEN
  51         IER = 20
  52         CALL XERFFT ('COSTF1',-5)
  53         GO TO 200
  54       ENDIF
  55 C
  56       SNM1 = 1./FLOAT(NM1)
  57       DSUM = SNM1*DSUM
  58       IF(MOD(NM1,2) .NE. 0) GO TO 30
  59       X(1,NM1) = X(1,NM1)+X(1,NM1)
  60    30 DO 105 I=3,N,2
  61          XI = .5*X(1,I)
  62          X(1,I) = .5*X(1,I-1)
  63          X(1,I-1) = DSUM
  64          DSUM = DSUM+XI
  65   105 CONTINUE
  66       IF (MODN .NE. 0) GO TO 117
  67       X(1,N) = DSUM
  68   117 X(1,1) = .5*X(1,1)
  69       X(1,N) = .5*X(1,N)
  70   200 RETURN
  71       END