Procedure

     CPOSR ( Character position, reverse )

     INTEGER FUNCTION CPOSR ( STR, CHARS, START )

Abstract

     Find the first occurrence in a string of a character belonging
     to a collection of characters, starting at a specified location,
     searching in reverse.

Required_Reading

     SCANNING

Keywords

     CHARACTER
     SEARCH
     UTILITY

Declarations

     IMPLICIT NONE

     CHARACTER*(*)         STR
     CHARACTER*(*)         CHARS
     INTEGER               START

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     STR        I   Any character string.
     CHARS      I   A collection of characters.
     START      I   Position to begin looking for one of CHARS

     The function returns the index of the last character of STR
     at or before index START that is in the collection CHARS.

Detailed_Input

     STR      is any character string.

     CHARS    is a character string containing a collection of
              characters. Spaces in CHARS are significant.

     START    is the position in STR to begin looking for one of the
              characters in CHARS.

Detailed_Output

     The function returns the index of the last character of STR (at
     or before index START) that is one of the characters in the
     string CHARS. If none of the characters is found, the function
     returns zero.

Parameters

     None.

Exceptions

     Error free.

     1)  If START is less than 1, CPOSR returns zero.

     2)  If START is greater than LEN(STRING), the search begins
         at the last character of the string.

Files

     None.

Particulars

     CPOSR is case sensitive.

     An entire family of related SPICELIB routines (POS, CPOS, NCPOS,
     POSR, CPOSR, NCPOSR) is described in the Required Reading.

     Those familiar with the True BASIC language should note that
     these functions are equivalent to the True BASIC intrinsic
     functions with the same name.

Examples

     Let STRING = 'BOB, JOHN, TED, AND MARTIN    '
                   123456789012345678901234567890

     Normal (sequential) searching:
     ------------------------------

           CPOSR( STRING, ' ,',    30 ) = 30

           CPOSR( STRING, ' ,',    29 ) = 29

           CPOSR( STRING, ' ,',    28 ) = 28

           CPOSR( STRING, ' ,',    27 ) = 27

           CPOSR( STRING, ' ,',    26 ) = 20

           CPOSR( STRING, ' ,',    19 ) = 16

           CPOSR( STRING, ' ,',    15 ) = 15

           CPOSR( STRING, ' ,',    14 ) = 11

           CPOSR( STRING, ' ,',    10 ) = 10

           CPOSR( STRING, ' ,',     9 ) =  5

           CPOSR( STRING, ' ,',     4 ) =  4

           CPOSR( STRING, ' ,',     3 ) =  0

     START out of bounds:
     --------------------

           CPOSR( STRING, ' ,',   231 ) = 30

           CPOSR( STRING, ' ,',    31 ) = 30

           CPOSR( STRING, ' ,',     0 ) =  0

           CPOSR( STRING, ' ,',   -10 ) =  0


     Order within CHARS
     ------------------

           CPOSR( STRING, 'JOHN',  23 ) =  18

           CPOSR( STRING, 'OHNJ',  23 ) =  18

           CPOSR( STRING, 'HNJO',  23 ) =  18

           CPOSR( STRING, 'NJOH',  23 ) =  18

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     J. Diaz del Rio    (ODC Space)
     H.A. Neilan        (JPL)
     B.V. Semenov       (JPL)
     W.L. Taber         (JPL)

Version

    SPICELIB Version 1.1.0, 13-AUG-2021 (JDR)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard.

    SPICELIB Version 1.0.3, 31-JAN-2008 (BVS)

        Removed non-standard end-of-declarations marker
        'C%&END_DECLARATIONS' from comments.

    SPICELIB Version 1.0.2, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.1, 26-MAR-1991 (HAN)

        The Required Reading file POSITION was renamed to SCANNING.
        This header was updated to reflect the change.

    SPICELIB Version 1.0.0, 31-JAN-1990 (WLT)