Scripts para marcar o desmarcar todos los checkbox de un formulario

Varias funciones javascript para marcar o desmarcar todos los checkbox de un formulario

function CheckAll()
{ count = document.form1.elements.length;
  for (i=0; i < count; i++)
    if(document.form1.elements[i].checked == 0)
      document.form1.elements[i].checked = 1;
}
function UncheckAll()
{ count = document.form1.elements.length;
  for (i=0; i < count; i++)
    if(document.form1.elements[i].checked == 1)
      document.form1.elements[i].checked = 0;
}
function ToogleAll()
{ count = document.form1.elements.length;
  for (i=0; i < count; i++)
    if(document.form1.elements[i].checked == 1)
      document.form1.elements[i].checked = 0;
    else
      document.form1.elements[i].checked = 1;
}