subroutine undflo(factor,expon)
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c     + + + PURPOSE + + +
c
c     SR UNDFLO protects against numeric underflows and overflows.
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c     Called from: Functions DEPEQ and DEPEND, SRS CASE12, CASE34,
c                  and ENRICH
c
c     Author(s): G. Foster, M. Nearing
c     Reference in user guide:
c
c     Changes:
c
c     Version: SR UNDFLO recoded from Version 90.92
c     Date recoded: 01/08/91
c     Recoded by: Charles R. Meyer
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c     + + + KEYWORDS + + +
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c     + + + ARGUMENT DECLARATIONS + + +
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      real factor, expon
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c     + + + ARGUMENT DEFINITIONS + + +
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c     factor -
c     expon  -
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c     + + + COMMON BLOCKS + + +
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c     + + + LOCAL VARIABLES + + +
c
      real exp10, power
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c     + + + LOCAL DEFINITIONS + + +
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c     exp10 -
c     power -
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c     + + + SAVES + + +
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c     + + + SUBROUTINES CALLED + + +
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c     + + + DATA INITIALIZATIONS + + +
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      data power /30.0/
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c     + + + END SPECIFICATIONS + + +
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      if (factor.ne.0.0) then
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        exp10 = expon * alog10(factor)
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        if (abs(exp10).gt.power) then
          factor = 0.0
          expon = 1.0
        end if
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      end if
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      return
      end