dichotomic_search_i_desc.F

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!||====================================================================
!||    dichotomic_search_i_desc   ../common_source/tools/search/dichotomic_search_i_desc.F
!||====================================================================
      FUNCTION dichotomic_search_i_desc(VAL, ARRAY, LEN)
C-----------------------------------------------
C   D e s c r i p t i o n
C-----------------------------------------------
C This subroutines is searching and returning the index in integer array ARRAY(1:LEN)
C such as ARRAY(index)<= VAL <ARRAY(index)
C Dichotomic search is used
C-----------------------------------------------
C   P r e c o n d i t i on
C-----------------------------------------------
C ARRAY(1:LEN) must be sorted integers (descending order)
C LEN >= 1
C VAL is an integer
C-----------------------------------------------
C   I m p l i c i t   T y p e s
C-----------------------------------------------
#include      "implicit_f.inc"
C-----------------------------------------------
C   D u m m y   A r g u m e n t s
C-----------------------------------------------
        INTEGER, INTENT(IN) :: VAL
        INTEGER, INTENT(IN) :: len
        INTEGER, INTENT(IN) :: array(len)
        INTEGER :: dichotomic_search_i_desc
C-----------------------------------------------
C   L o c a l   V a r i a b l e s
C-----------------------------------------------
        INTEGER :: imid,istart,iend
C-----------------------------------------------
C   S o u r c e   L i n e s
C-----------------------------------------------
        istart = 1
        iend = len
        !VAL ABOVE UPPER BOUND
        IF(array(1)<val)THEN
          dichotomic_search_i_desc = 1
          RETURN
        ENDIF
        !VAL LOWER THAN LOWER BOUND
        IF(array(len)>val)THEN
          dichotomic_search_i_desc = len
          RETURN
        ENDIF
        !VAL IS BETWEEN THE BOUNDS
        DO WHILE (istart+1<iend)
          imid=(iend+istart)/2
          IF(array(imid) < val)THEN
            !FOCUS ON LEFT PART
            iend = imid
          ELSEIF(array(imid) > val)THEN
            !FOCUS ON RIGHT PART
            istart = imid
          ELSE
            !FOUND BY CHANCE NO NEED TO ITERATE MORE
            dichotomic_search_i_desc = imid
            RETURN
          ENDIF
        ENDDO
        dichotomic_search_i_desc = istart
        RETURN
      END FUNCTION dichotomic_search_i_desc