# Natural logarithm.
#
# Note that we use the mathematics / Javascript / Mathematica
# convention that "log" is indeed the natural logarithm.
#
# In engineering, biology, astronomy, "log" can stand instead
# for the "common" logarithm i.e. base 10. Also note that Google
# calculations use log for the common logarithm.


Eval_log = ->
  push(cadr(p1))
  Eval()
  logarithm()

logarithm = ->
  save()
  yylog()
  restore()

yylog = ->
  d = 0.0

  p1 = pop()

  if (p1 == symbol(E))
    push_integer(1)
    return

  if (equaln(p1, 1))
    push_integer(0)
    return

  if (isnegativenumber(p1))
    push(p1)
    negate()
    logarithm()
    push(imaginaryunit)
    if evaluatingAsFloats
      push_double(Math.PI)
    else
      push_symbol(PI)
    multiply()
    add()
    return

  if (isdouble(p1))
    d = Math.log(p1.d)
    push_double(d)
    return

  # rational number and not an integer?

  if (isfraction(p1))
    push(p1)
    numerator()
    logarithm()
    push(p1)
    denominator()
    logarithm()
    subtract()
    return

  # log(a ^ b) --> b log(a)

  if (car(p1) == symbol(POWER))
    push(caddr(p1))
    push(cadr(p1))
    logarithm()
    multiply()
    return

  # log(a * b) --> log(a) + log(b)

  if (car(p1) == symbol(MULTIPLY))
    push_integer(0)
    p1 = cdr(p1)
    while (iscons(p1))
      push(car(p1))
      logarithm()
      add()
      p1 = cdr(p1)
    return

  push_symbol(LOG)
  push(p1)
  list(2)