dpchst.f

Go to the documentation of this file.

*DECK DPCHST
      DOUBLE PRECISION FUNCTION dpchst (ARG1, ARG2)
C***BEGIN PROLOGUE  DPCHST
C***SUBSIDIARY
C***PURPOSE  DPCHIP Sign-Testing Routine
C***LIBRARY   SLATEC (PCHIP)
C***TYPE      DOUBLE PRECISION (PCHST-S, DPCHST-D)
C***AUTHOR  Fritsch, F. N., (LLNL)
C***DESCRIPTION
C
C         DPCHST:  DPCHIP Sign-Testing Routine.
C
C
C     Returns:
C        -1. if ARG1 and ARG2 are of opposite sign.
C         0. if either argument is zero.
C        +1. if ARG1 and ARG2 are of the same sign.
C
C     The object is to do this without multiplying ARG1*ARG2, to avoid
C     possible over/underflow problems.
C
C  Fortran intrinsics used:  SIGN.
C
C***SEE ALSO  DPCHCE, DPCHCI, DPCHCS, DPCHIM
C***ROUTINES CALLED  (NONE)
C***REVISION HISTORY  (YYMMDD)
C   811103  DATE WRITTEN
C   820805  Converted to SLATEC library version.
C   870813  Minor cosmetic changes.
C   890411  Added SAVE statements (Vers. 3.2).
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   890531  REVISION DATE from Version 3.2
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900328  Added TYPE section.  (WRB)
C   910408  Updated AUTHOR and DATE WRITTEN sections in prologue.  (WRB)
C   930503  Improved purpose.  (FNF)
C***END PROLOGUE  DPCHST
C
C**End
C
C  DECLARE ARGUMENTS.
C
      DOUBLE PRECISION  arg1, arg2
C
C  DECLARE LOCAL VARIABLES.
C
      DOUBLE PRECISION  one, zero
      SAVE zero, one
      DATA  zero /0.d0/,  one/1.d0/
C
C  PERFORM THE TEST.
C
C***FIRST EXECUTABLE STATEMENT  DPCHST
      dpchst = sign(one,arg1) * sign(one,arg2)
      IF ((arg1.EQ.zero) .OR. (arg2.EQ.zero))  dpchst = zero
C
      RETURN
C------------- LAST LINE OF DPCHST FOLLOWS -----------------------------
      END