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R2795/MITgcm_orig_code/MITgcm/eesupp/src/diff_phase_multiple.F
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diff_phase_multiple.F
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C $Header: /u/gcmpack/MITgcm/eesupp/src/diff_phase_multiple.F,v 1.4 2007/03/03 22:35:46 jmc Exp $
C $Name: $
#include "CPP_EEOPTIONS.h"
CBOP
C !ROUTINE: DIFF_PHASE_MULTIPLE
C !INTERFACE:
LOGICAL FUNCTION DIFF_PHASE_MULTIPLE( phase, freq, val1, step )
IMPLICIT NONE
C !DESCRIPTION:
C *==========================================================*
C | LOGICAL FUNCTION DIFF\_PHASE\_MULTIPLE
C | o Checks if a multiple of freq (+ phase shift) 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 phase :: shift phase time
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 phase, 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.
DIFF_PHASE_MULTIPLE = .FALSE.
IF ( freq .NE. 0. ) THEN
IF ( ABS(step) .GT. ABS(freq) ) THEN
DIFF_PHASE_MULTIPLE = .TRUE.
c ELSEIF ( val1+step .GE. phase+baseTime ) THEN
C- should compare to phase+baseTime (above), but would need PARAMS.h ;
C choose to disable this condition for negative time:
ELSEIF ( val1+step.GE.phase .OR. val1.LT.0. ) THEN
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 = phase + NINT((v1-phase)/freq)*freq
d1 = v1-v4
d2 = v2-v4
d3 = v3-v4
IF ( ABS(d1) .LT. ABS(d2) .AND. ABS(d1) .LE. ABS(d3) )
& DIFF_PHASE_MULTIPLE = .TRUE.
ENDIF
ENDIF
RETURN
END
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