share/fftpack5/fortran/xercon.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       LOGICAL FUNCTION XERCON (INC,JUMP,N,LOT)
  12       INTEGER INC, JUMP, N, LOT
  13       INTEGER I, J, JNEW, LCM
  14 C
  15 C     Definition: positive integers INC, JUMP, N and LOT are consistent
  16 C                                                            ----------
  17 C     if I1*INC + J1*JUMP = I2*INC + J2*JUMP for I1,I2 < N and J1,J2
  18 C     < LOT implies I1=I2 and J1=J2.
  19 C
  20 C     For multiple FFTs to execute correctly, input parameters INC,
  21 C     JUMP, N and LOT must be consistent ... otherwise at least one
  22 C     array element mistakenly is transformed more than once.
  23 C
  24 C     XERCON = .TRUE. if and only if INC, JUMP, N and LOT are
  25 C     consistent.
  26 C
  27 C     ------------------------------------------------------------------
  28 C
  29 C     Compute I = greatest common divisor (INC, JUMP)
  30 C
  31       I = INC
  32       J = JUMP
  33    10 CONTINUE
  34       IF (J .NE. 0) THEN
  35         JNEW = MOD(I,J)
  36         I    = J
  37         J    = JNEW
  38         GO TO 10
  39       ENDIF
  40 C
  41 C Compute LCM = least common multiple (INC, JUMP)
  42 C
  43       LCM = (INC*JUMP)/I
  44 C
  45 C Check consistency of INC, JUMP, N, LOT
  46 C
  47       IF (LCM .LE. (N-1)*INC .AND. LCM .LE. (LOT-1)*JUMP) THEN
  48         XERCON = .FALSE.
  49       ELSE
  50         XERCON = .TRUE.
  51       ENDIF
  52 C
  53       RETURN
  54       END