### arccosh =====================================================================

Tags
----
scripting, JS, internal, treenode, general concept

Parameters
----------
x

General description
-------------------
Returns the inverse hyperbolic cosine of x.

###

Eval_arccosh = ->
  push(cadr(p1))
  Eval()
  arccosh()

arccosh = ->
  d = 0.0
  save()
  p1 = pop()
  if (car(p1) == symbol(COSH))
    push(cadr(p1))
    restore()
    return

  if (isdouble(p1))
    d = p1.d
    if (d < 1.0)
      stop("arccosh function argument is less than 1.0")
    d = Math.log(d + Math.sqrt(d * d - 1.0))
    push_double(d)
    restore()
    return

  if (isplusone(p1))
    push(zero)
    restore()
    return

  push_symbol(ARCCOSH)
  push(p1)
  list(2)
  restore()