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## -*- texinfo -*-
## @deftypefn  {} {@var{v} =} findstr (@var{s}, @var{t})
## @deftypefnx {} {@var{v} =} findstr (@var{s}, @var{t}, @var{overlap})
##
## This function is obsolete.  Use @code{strfind} instead.
##
## Return the vector of all positions in the longer of the two strings @var{s}
## and @var{t} where an occurrence of the shorter of the two starts.
##
## If the optional argument @var{overlap} is true (default), the returned
## vector can include overlapping positions.  For example:
##
## @example
## @group
## findstr ("ababab", "a")
##      @result{} [1, 3, 5];
## findstr ("abababa", "aba", 0)
##      @result{} [1, 5]
## @end group
## @end example
##
## @strong{Caution:} @code{findstr} is obsolete.  Use @code{strfind} in all new
## code.
## @seealso{strfind, strmatch, strcmp, strncmp, strcmpi, strncmpi, find}
## @end deftypefn

## Note that this implementation swaps the strings if second one is longer
## than the first, so try to put the longer one first.

function v = findstr (s, t, overlap = true)

  persistent warned = false;
  if (! warned)
    warned = true;
    warning ("Octave:legacy-function",
             "findstr is obsolete; use strfind instead\n");
  endif

  if (nargin < 2)
    print_usage ();
  endif

  if (all (size (s) > 1) || all (size (t) > 1))
    error ("findstr: arguments must have only one non-singleton dimension");
  endif

  ## Make S be the longer string.
  if (length (s) < length (t))
    [s, t] = deal (t, s);
  endif

  l_s = length (s);
  l_t = length (t);

  if (l_t == 0)
    ## zero length target: return empty set
    v = [];

  elseif (l_t == 1)
    ## length one target: simple find
    v = find (s == t);

  elseif (l_t == 2)
    ## length two target: find first at i and second at i+1
    v = find (s(1:l_s-1) == t(1) & s(2:l_s) == t(2));

  else
    ## length three or more: match the first three by find then go through
    ## the much smaller list to determine which of them are real matches
    limit = l_s - l_t + 1;
    v = find (  s(1:limit)   == t(1)
              & s(2:limit+1) == t(2)
              & s(3:limit+2) == t(3));
  endif

  ## Need to search the index vector if our find was too short
  ## (target length > 3), or if we don't allow overlaps.  Note though
  ## that there cannot be any overlaps if the first character in the
  ## target is different from the remaining characters in the target,
  ## so a single character, two different characters, or first character
  ## different from the second two don't need to be searched.
  if (l_t >= 3 || (! overlap && l_t > 1 && any (t(1) == t(2:l_t))))
    ## force strings to be both row vectors or both column vectors
    if (all (size (s) != size (t)))
      t = t.';
    endif

    ## determine which ones to keep
    keep = zeros (size (v));
    ind = 0:l_t-1;
    if (overlap)
      for idx = 1:length (v)
        keep(idx) = all (s(v(idx) + ind) == t);
      endfor
    else
      ## First possible position for next non-overlapping match.
      next = 1;
      for idx = 1:length (v)
        if (v(idx) >= next && s(v(idx) + ind) == t)
          keep(idx) = 1;
          ## Skip to the next possible match position.
          next = v(idx) + l_t;
        else
          keep(idx) = 0;
        endif
      endfor
    endif
    if (! isempty (v))
      v = v(find (keep));
    endif
  endif

  if (isempty (v))
    v = [];
  endif

  ## Always return a row vector, because that's what the old one did.
  if (iscolumn (v))
    v = v.';
  endif

endfunction


## First test is necessary to provoke 1-time legacy warning
%!test
%! warning ("off", "Octave:legacy-function", "local");
%! findstr ("", "");

%!assert (findstr ("abababa", "a"), [1, 3, 5, 7])
%!assert (findstr ("abababa", "aba"), [1, 3, 5])
%!assert (findstr ("aba", "abababa", 0), [1, 5])

## Test input validation
%!error <Invalid call> findstr ()
%!error <Invalid call> findstr ("str1")
%!error <must have only one non-singleton dimension> findstr (["AB" ; "CD"], "C")