#-----------------------------------------------------------------------------
#
#  Author : philippe.billet@noos.fr
#
#  Gamma function gamma(x)
#  
#-----------------------------------------------------------------------------




Eval_gamma = ->
  push(cadr(p1))
  Eval()
  gamma()

gamma = ->
  save()
  gammaf()
  restore()

gammaf = ->
  #  double d

  p1 = pop()

  if (isrational(p1) && MEQUAL(p1.q.a, 1) && MEQUAL(p1.q.b, 2))
    if evaluatingAsFloats
      push_double(Math.PI)
    else
      push_symbol(PI)
    push_rational(1,2)
    power()
    return

  if (isrational(p1) && MEQUAL(p1.q.a, 3) && MEQUAL(p1.q.b, 2))
    if evaluatingAsFloats
      push_double(Math.PI)
    else
      push_symbol(PI)
    push_rational(1,2)
    power()
    push_rational(1,2)
    multiply()
    return
  
  #  if (p1->k == DOUBLE) {
  #    d = exp(lgamma(p1.d))
  #    push_double(d)
  #    return
  #  }

  if (isnegativeterm(p1))
    if evaluatingAsFloats
      push_double(Math.PI)
    else
      push_symbol(PI)
    push_integer(-1)
    multiply()
    if evaluatingAsFloats
      push_double(Math.PI)
    else
      push_symbol(PI)
    push(p1)
    multiply()
    sine()
    push(p1)
    multiply()
    push(p1)
    negate()
    gamma()
    multiply()
    divide()
    return
  
  if (car(p1) == symbol(ADD))
    gamma_of_sum()
    return
  
    
  push_symbol(GAMMA)
  push(p1)
  list(2)
  return

gamma_of_sum = ->
  p3 = cdr(p1)
  if (isrational(car(p3)) && MEQUAL(car(p3).q.a, 1) && MEQUAL(car(p3).q.b, 1))
    push(cadr(p3))
    push(cadr(p3))
    gamma()
    multiply()
  else
    if (isrational(car(p3)) && MEQUAL(car(p3).q.a, -1) && MEQUAL(car(p3).q.b, 1))
      push(cadr(p3))
      gamma()
      push(cadr(p3))
      push_integer(-1)
      add()
      divide()
    else
      push_symbol(GAMMA)
      push(p1)
      list(2)
      return