pchst.f

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00001 *DECK PCHST
00002       REAL FUNCTION PCHST (ARG1, ARG2)
00003 C***BEGIN PROLOGUE  PCHST
00004 C***SUBSIDIARY
00005 C***PURPOSE  PCHIP Sign-Testing Routine
00006 C***LIBRARY   SLATEC (PCHIP)
00007 C***TYPE      SINGLE PRECISION (PCHST-S, DPCHST-D)
00008 C***AUTHOR  Fritsch, F. N., (LLNL)
00009 C***DESCRIPTION
00010 C
00011 C         PCHST:  PCHIP Sign-Testing Routine.
00012 C
00013 C     Returns:
00014 C        -1. if ARG1 and ARG2 are of opposite sign.
00015 C         0. if either argument is zero.
00016 C        +1. if ARG1 and ARG2 are of the same sign.
00017 C
00018 C     The object is to do this without multiplying ARG1*ARG2, to avoid
00019 C     possible over/underflow problems.
00020 C
00021 C  Fortran intrinsics used:  SIGN.
00022 C
00023 C***SEE ALSO  PCHCE, PCHCI, PCHCS, PCHIM
00024 C***ROUTINES CALLED  (NONE)
00025 C***REVISION HISTORY  (YYMMDD)
00026 C   811103  DATE WRITTEN
00027 C   820805  Converted to SLATEC library version.
00028 C   870813  Minor cosmetic changes.
00029 C   890411  Added SAVE statements (Vers. 3.2).
00030 C   890411  REVISION DATE from Version 3.2
00031 C   891214  Prologue converted to Version 4.0 format.  (BAB)
00032 C   900328  Added TYPE section.  (WRB)
00033 C   910408  Updated AUTHOR and DATE WRITTEN sections in prologue.  (WRB)
00034 C   930503  Improved purpose.  (FNF)
00035 C***END PROLOGUE  PCHST
00036 C
00037 C**End
00038 C
00039 C  DECLARE ARGUMENTS.
00040 C
00041       REAL  ARG1, ARG2
00042 C
00043 C  DECLARE LOCAL VARIABLES.
00044 C
00045       REAL  ONE, ZERO
00046       SAVE ZERO, ONE
00047       DATA  ZERO /0./,  ONE /1./
00048 C
00049 C  PERFORM THE TEST.
00050 C
00051 C***FIRST EXECUTABLE STATEMENT  PCHST
00052       PCHST = SIGN(ONE,ARG1) * SIGN(ONE,ARG2)
00053       IF ((ARG1.EQ.ZERO) .OR. (ARG2.EQ.ZERO))  PCHST = ZERO
00054 C
00055       RETURN
00056 C------------- LAST LINE OF PCHST FOLLOWS ------------------------------
00057       END
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