function y = prepad (x, l, c)

# prepad (x, l)
#
# Prepends zeros to the vector x until it is of length l.
# prepad(x,l,c) prepends the constant c instead of zero.
#
# If length (x) > l, elements from the beginning of x are removed
# until a vector of length l is obtained.

# Author:
#  Tony Richardson
#  amr@mpl.ucsd.edu
#  June 1994

  if (nargin == 2)
    c = 0;
  elseif (nargin < 2 || nargin > 3)
    usage ("prepad (x, l) or prepad (x, l, c)");
  endif

  if (is_matrix (x))
    error ("first argument must be a vector");
  elseif (! is_scalar (l))
    error ("second argument must be a scaler");
  endif

  if (l < 0)
    error ("second argument must be non-negative");
  endif

  lx = length (x);

  if (lx >= l)
    y = x(lx-l+1:lx);
  else
    if (rows (x) > 1)
      tmp = c * ones (l-lx, 1);
      y = [tmp; x];
    else
      tmp = c * ones (1, l-lx);
      y = [tmp, x];
    endif
  endif

endfunction