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defmodule ElixirMathParser.Math.Calc do
alias ElixirMathParser.Math.Rational
def factorial(n), do: factorial_rec(n, 1)
defp factorial_rec(n, acc) when n > 0, do: factorial_rec(n - 1, acc * n)
defp factorial_rec(0, acc), do: acc
def pow(value, exponent), do: pow_rec(value, exponent, Rational.new(1))
defp pow_rec(value, exponent, acc) when is_integer(exponent) do
case exponent do
0 ->
acc
_ when exponent < 0 ->
pow_rec(Rational.new(1, value), -exponent, acc)
_ when Kernel.rem(exponent, 2) == 0 ->
pow_rec(Rational.mult(value, value), Kernel.div(exponent, 2), acc)
_ ->
pow_rec(
Rational.mult(value, value),
Kernel.div(exponent - 1, 2),
Rational.mult(acc, value)
)
end
end
end
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