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pchst.f
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1 *DECK PCHST
2  REAL FUNCTION pchst (ARG1, ARG2)
3 C***BEGIN PROLOGUE PCHST
4 C***SUBSIDIARY
5 C***PURPOSE PCHIP Sign-Testing Routine
6 C***LIBRARY SLATEC (PCHIP)
7 C***TYPE SINGLE PRECISION (PCHST-S, DPCHST-D)
8 C***AUTHOR Fritsch, F. N., (LLNL)
9 C***DESCRIPTION
10 C
11 C PCHST: PCHIP Sign-Testing Routine.
12 C
13 C Returns:
14 C -1. if ARG1 and ARG2 are of opposite sign.
15 C 0. if either argument is zero.
16 C +1. if ARG1 and ARG2 are of the same sign.
17 C
18 C The object is to do this without multiplying ARG1*ARG2, to avoid
19 C possible over/underflow problems.
20 C
21 C Fortran intrinsics used: SIGN.
22 C
23 C***SEE ALSO PCHCE, PCHCI, PCHCS, PCHIM
24 C***ROUTINES CALLED (NONE)
25 C***REVISION HISTORY (YYMMDD)
26 C 811103 DATE WRITTEN
27 C 820805 Converted to SLATEC library version.
28 C 870813 Minor cosmetic changes.
29 C 890411 Added SAVE statements (Vers. 3.2).
30 C 890411 REVISION DATE from Version 3.2
31 C 891214 Prologue converted to Version 4.0 format. (BAB)
32 C 900328 Added TYPE section. (WRB)
33 C 910408 Updated AUTHOR and DATE WRITTEN sections in prologue. (WRB)
34 C 930503 Improved purpose. (FNF)
35 C***END PROLOGUE PCHST
36 C
37 C**End
38 C
39 C DECLARE ARGUMENTS.
40 C
41  REAL ARG1, ARG2
42 C
43 C DECLARE LOCAL VARIABLES.
44 C
45  REAL ONE, ZERO
46  SAVE zero, one
47  DATA zero /0./, one /1./
48 C
49 C PERFORM THE TEST.
50 C
51 C***FIRST EXECUTABLE STATEMENT PCHST
52  pchst = sign(one,arg1) * sign(one,arg2)
53  IF ((arg1.EQ.zero) .OR. (arg2.EQ.zero)) pchst = zero
54 C
55  RETURN
56 C------------- LAST LINE OF PCHST FOLLOWS ------------------------------
57  END