FUNCTION LOCATE(STRING,SLEN,IBEG,P,PATERN,PLEN)
C This file: http://ftp.aset.psu.edu/pub/ger/fortran/hdk/substr.f90
C
C=========LOCATE IS A SCANNING FUNCTION WHICH SCANS THE
C     STRING, "STRING" OF LENGTH "SLEN" BEGINNING AT STRING(|IBEG|)
C     FOR THE FIRST OCCURENCE OF THE SUBSTRING "PATERN" OF
C     LENGTH "PLEN".  IF P IS .TRUE. THEN THE INDEX OF THE FIRST
C     OCCURENCE WHERE THE SUBSTRING OF "STRING" EQUALS "PATERN" IS
C     RETURNED; IF P IS .FALSE. THEN THE INDEX OF THE FIRST
C     OCCURENCE WHERE ANY SUBSTRING OF "STRING" IS NOT EQUAL
C     TO "PATERN" IS RETURNED.
C     IF IBEG IS POSITIVE THEN THE SCAN IS (FORWARD) TOWARDS
C     STRING(SLEN); IF IBEG IS NEGATIVE THEN THE SCAN IS
C     (BACKWARD) TOWARD STRING(1).
C     IF P IS TRUE AND "PATTERN" IS NOT A SUBSTRING OF "STRING" OR
C     IF P IS FALSE AND "STRING" IS EXACTLY EQUAL TO "PATERN"
C     THEN LOCATE IS RETURNED ZERO.  IF "STRING" OR "PATERN"
C     ARE NULL OR "PATERN" IS LONGER THAN "STRING" THEN LOCATE
C     IS RETURNED ZERO.  OTHERWISE LOCATE IS RETURNED AS A
C     INDEX SUCH THAT THE SUBSTRING BEGINNING AT STRING(LOCATE)
C     OF LENGTH PLEN IS EQUAL TO PATERN.
C                     HDK - 1978
C
      INTEGER SLEN,PLEN
      LOGICAL P,CEQ
C,    CHARACTER*1 STRING(SLEN),PATERN(PLEN)
      LOGICAL*1 STRING(SLEN),PATERN(PLEN)
      IF(IBEG.LT.0) GO TO 1
C----------SCAN NSCANS FORWARD BEGINNING AT STRING(LOCATE).
      NSCANS=CLEN-PLEN-IBEG+1
      LOCATE=IBEG
      GO TO 2
C----------SCAN NSCANS BACKWARD BEGINNING AT STRING(LOCATE).
1     NSCANS=-IBEG-PLEN
      LOCATE=NSCANS
2     INCR=ISIGN(1,IBEG)
      IF(IBEG.EQ.0 .OR. PLEN.LT.1 .OR. NSCANS.LT.1) GO TO 4
C----------DO THE SCAN.
      DO 3 I=1,NSCANS
      IF(CEQ(CARD(LOCATE),PAT,PLEN).AND.P) GO TO 5
3     LOCATE=LOCATE+INCR
4     LOCATE=0
5     RETURN
      END