instr.for

C **********************************************************************
C *                                                                    *
C * INSTR - IS STRING Y$ CONTAINED IN STRING X$, BEGINNING AT POSITION *
C *         I. Y$ IS NEEDLE (N$), X$ IS HAYSTACK (H$)                  *
C *                                                                    *
C * FROM MBASIC.                                                       *
C *                                                                    *
C **********************************************************************
C
      INTEGER FUNCTION INSTR(I, X$, Y$)
      INTEGER I
      REAL X$, Y$
C
      REAL N$
      INTEGER IN$(2), N$OFF, N$LEN
      REAL H$
      INTEGER IH$(2), H$OFF, H$LEN
      INTEGER J, K, L, P, Q
C
      INCLUDE STRING.INC
C
      EQUIVALENCE (N$, IN$(1)), (IN$(1), N$OFF), (IN$(2), N$LEN)
      EQUIVALENCE (H$, IH$(1)), (IH$(1), H$OFF), (IH$(2), H$LEN)
C
      N$ = Y$
      H$ = X$
      INSTR = I
      IF (N$LEN .LE. 0) GO TO 2
      INSTR = 0
      IF (H$LEN .LE. 0) GO TO 2
      IF (I .GT. H$LEN) GO TO 2
      DO 1 J = I, H$LEN
        P = H$OFF + J - 1
        DO 3 K=1,N$LEN
          IF (J + K - 1 .GT. H$LEN) GO TO 1
          Q = N$OFF + K - 1
          L = P + K - 1
          IF (STRDAT(L) .NE. STRDAT(Q)) GO TO 1
    3   CONTINUE
        INSTR = J
        GO TO 2
    1 CONTINUE
    2 RETURN
      END