Some fixes for logarithms (#21)

* Some fixes for logarithms

* chore: format and tests

* chore: bump patch

Co-authored-by: Paulo Valente <16843419+polvalente@users.noreply.github.com>

Author: seanmor5

lib/complex.ex

@@ -865,6 +865,8 @@ defmodule Complex do
   def ln(:infinity), do: :infinity
   def ln(:neg_infinity), do: new(:infinity, :math.pi())
   def ln(:nan), do: :nan
+  def ln(n) when is_number(n) and n == 0, do: :neg_infinity
+  def ln(n) when is_number(n) and n < 0, do: :nan
   def ln(n) when is_number(n), do: :math.log(n)
 
   def ln(z = %Complex{}) do
@@ -891,6 +893,8 @@ defmodule Complex do
   def log10(:infinity), do: :infinity
   def log10(:neg_infinity), do: divide(ln(:neg_infinity), :math.log(10))
   def log10(:nan), do: :nan
+  def log10(n) when is_number(n) and n == 0, do: :neg_infinity
+  def log10(n) when is_number(n) and n < 0, do: :nan
 
   def log10(n) when is_number(n), do: :math.log10(n)
 
@@ -918,6 +922,8 @@ defmodule Complex do
   def log2(:infinity), do: :infinity
   def log2(:neg_infinity), do: divide(ln(:neg_infinity), :math.log(2))
   def log2(:nan), do: :nan
+  def log2(n) when is_number(n) and n == 0, do: :neg_infinity
+  def log2(n) when is_number(n) and n < 0, do: :nan
 
   def log2(n) when is_number(n), do: :math.log2(n)
 

mix.exs

@@ -4,7 +4,7 @@ defmodule Complex.Mixfile do
   def project do
     [
       app: :complex,
-      version: "0.4.1",
+      version: "0.4.2",
       description: description(),
       package: package(),
       elixir: "~> 1.12",

test/complex_test.exs

@@ -384,6 +384,22 @@ defmodule ComplexTest do
     assert_close Complex.log10(a), :math.log10(a)
     assert_close Complex.log2(a), :math.log2(a)
     assert_close Complex.power(a, b), :math.pow(a, b)
+
+    assert Complex.ln(0) == :neg_infinity
+    assert Complex.log10(0) == :neg_infinity
+    assert Complex.log2(0) == :neg_infinity
+
+    assert Complex.ln(:infinity) == :infinity
+    assert Complex.log10(:infinity) == :infinity
+    assert Complex.log2(:infinity) == :infinity
+
+    assert Complex.ln(-1) == :nan
+    assert Complex.log10(-1) == :nan
+    assert Complex.log2(-1) == :nan
+
+    assert Complex.ln(:nan) == :nan
+    assert Complex.log10(:nan) == :nan
+    assert Complex.log2(:nan) == :nan
   end
 
   test "power (non-finite)" do