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59 lines
1.7 KiB
Fortran
59 lines
1.7 KiB
Fortran
*DECK DPCHST
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DOUBLE PRECISION FUNCTION DPCHST (ARG1, ARG2)
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C***BEGIN PROLOGUE DPCHST
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C***SUBSIDIARY
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C***PURPOSE DPCHIP Sign-Testing Routine
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C***LIBRARY SLATEC (PCHIP)
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C***TYPE DOUBLE PRECISION (PCHST-S, DPCHST-D)
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C***AUTHOR Fritsch, F. N., (LLNL)
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C***DESCRIPTION
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C
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C DPCHST: DPCHIP Sign-Testing Routine.
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C
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C
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C Returns:
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C -1. if ARG1 and ARG2 are of opposite sign.
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C 0. if either argument is zero.
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C +1. if ARG1 and ARG2 are of the same sign.
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C
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C The object is to do this without multiplying ARG1*ARG2, to avoid
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C possible over/underflow problems.
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C
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C Fortran intrinsics used: SIGN.
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C
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C***SEE ALSO DPCHCE, DPCHCI, DPCHCS, DPCHIM
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C***ROUTINES CALLED (NONE)
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C***REVISION HISTORY (YYMMDD)
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C 811103 DATE WRITTEN
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C 820805 Converted to SLATEC library version.
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C 870813 Minor cosmetic changes.
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C 890411 Added SAVE statements (Vers. 3.2).
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C 890531 Changed all specific intrinsics to generic. (WRB)
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C 890531 REVISION DATE from Version 3.2
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 900328 Added TYPE section. (WRB)
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C 910408 Updated AUTHOR and DATE WRITTEN sections in prologue. (WRB)
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C 930503 Improved purpose. (FNF)
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C***END PROLOGUE DPCHST
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C
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C**End
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C
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C DECLARE ARGUMENTS.
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C
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DOUBLE PRECISION ARG1, ARG2
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C
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C DECLARE LOCAL VARIABLES.
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C
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DOUBLE PRECISION ONE, ZERO
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SAVE ZERO, ONE
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DATA ZERO /0.D0/, ONE/1.D0/
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C
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C PERFORM THE TEST.
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C
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C***FIRST EXECUTABLE STATEMENT DPCHST
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DPCHST = SIGN(ONE,ARG1) * SIGN(ONE,ARG2)
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IF ((ARG1.EQ.ZERO) .OR. (ARG2.EQ.ZERO)) DPCHST = ZERO
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C
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RETURN
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C------------- LAST LINE OF DPCHST FOLLOWS -----------------------------
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END
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