C $Header: /u/gcmpack/MITgcm/eesupp/src/different_multiple.F,v 1.9 2005/09/27 18:38:28 jmc Exp $ C $Name: $ #include "CPP_EEOPTIONS.h" CBOP C !ROUTINE: DIFFERENT_MULTIPLE C !INTERFACE: LOGICAL FUNCTION DIFFERENT_MULTIPLE( freq, val1, step ) IMPLICIT NONE C !DESCRIPTION: C *==========================================================* C | LOGICAL FUNCTION DIFFERENT\_MULTIPLE C | o Checks if a multiple of freq exist C | around val1 +/- step/2 C *==========================================================* C | This routine is used for diagnostic and other periodic C | operations. It is very sensitive to arithmetic precision. C | For IEEE conforming arithmetic it works well but for C | cases where short cut arithmetic is used it may not work C | as expected. To overcome this issue compile this routine C | separately with no optimisation. C *==========================================================* C !INPUT PARAMETERS: C == Routine arguments == C freq :: Frequency by which time is divided. C val1 :: time that is checked C step :: length of time interval (around val1) that is checked _RL freq, val1, step C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----| C !LOCAL VARIABLES: C == Local variables == C v1, v2, v3, v4 :: Temp. for holding time C d1, d2, d3 :: Temp. for hold difference _RL v1, v2, v3, v4, d1, d2, d3 CEOP C o Do easy cases first. DIFFERENT_MULTIPLE = .FALSE. IF ( freq .NE. 0. ) THEN IF ( ABS(step) .GT. freq ) THEN DIFFERENT_MULTIPLE = .TRUE. ELSE C o This case is more complex because of round-off error v1 = val1 v2 = val1 - step v3 = val1 + step C Test v1 to see if its a "closest multiple" v4 = NINT(v1/freq)*freq d1 = v1-v4 d2 = v2-v4 d3 = v3-v4 IF ( ABS(d1) .LT. ABS(d2) .AND. ABS(d1) .LE. ABS(d3) ) & DIFFERENT_MULTIPLE = .TRUE. ENDIF ENDIF RETURN END