code: function sc_vectorCopyBang(target, tstart, source, sstart, send) {
      if (!sstart) sstart = 0;
      if (!send) send = source.length;
  
      // if target == source we don't want to overwrite not yet copied elements.
      if (tstart <= sstart) {
  	for (var i = tstart, j = sstart; j < send; i++, j++) {
  	    target[i] = source[j];
  	}
      } else {
  	var diff = send - sstart;
  	for (var i = tstart + diff - 1, j = send - 1;
  	     j >= sstart;
  	     i--, j--) {
  	    target[i] = source[j];
  	}
      }
      return target;
  }
docs: * META ((export #t))