c $Header: /usr/people/flittner/radtran/tomrad/pv2.2/src/RCS/findex.f,v 2.22 2000/08/30 16:38:09 flittner Exp $
      subroutine findex(xa,n,x,klo,khi)
c
c given an array of values in order, find the index of the 2 pts that stradle x
c
c last modified: August 5, 1997...def
c purpose: add tollerance for comparisons. This is in the const.inc file.
c
      implicit none
c the rcs revision #
      character*20 rcsrev
      parameter (rcsrev='$Revision: 2.22 $')
c
      include 'consts.cmn'
      integer n,klo,khi,k
      real*8 xa(n),x
c
c check to see if the data is increasing in the independent variable
c or decreasing
c
      klo = 1
      khi = n
      if(xa(khi).gt.xa(klo))then
        if(x-xa(1).lt.smallx)then
          klo=1
          khi=2
          return
        else if(xa(n)-x.lt.smallx)then
          klo=n-1
          khi=n
          return
        endif
10      continue
        if (khi-klo .gt. 1) then
           k = (khi+klo)/2
           if (abs(x-xa(k)).lt.smallx) then
              klo = k
              khi = klo+1
              return
           else if (x-xa(k).lt.smallx) then
              khi = k
           else
              klo = k
           endif
           goto 10
        endif
      else
        if(x-xa(n).lt.smallx)then
          klo=n-1
          khi=n
          return
        else if(xa(1)-x.lt.smallx)then
          klo=1
          khi=2
          return
        endif
15      continue
        if (khi-klo.gt. 1) then
           k = (khi+klo)/2
           if (abs(x-xa(k)).lt.smallx) then
              klo = k
              khi = klo+1
              return
           else if (x-xa(k).lt.smallx) then
              klo = k
           else
              khi = k
           endif
           goto 15
        endif
      endif
      return
      end