Provide helpers for NaN and ±infinity packing (#57)

lexmag · Dec 29, 2020 · 8486a10 · 8486a10
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Showing 3 changed files with 30 additions and 6 deletions.
diff --git a/lib/msgpax.ex b/lib/msgpax.ex
@@ -15,23 +15,25 @@ defmodule Msgpax do
   `false`                           | boolean       | `false`
   `-1`                              | integer       | `-1`
   `1.25`                            | float         | `1.25`
-  *N/A*                             | NaN           | `Msgpax.NaN`<sup>1</sup>
-  *N/A*                             | +infinity     | `Msgpax.Infinity`<sup>1</sup>
-  *N/A*                             | -infinity     | `Msgpax.NegInfinity`<sup>1</sup>
+  *N/A*<sup>1</sup>                 | NaN           | `Msgpax.NaN`<sup>2</sup>
+  *N/A*<sup>1</sup>                 | +infinity     | `Msgpax.Infinity`<sup>2</sup>
+  *N/A*<sup>1</sup>                 | -infinity     | `Msgpax.NegInfinity`<sup>2</sup>
   `:ok`                             | string        | `"ok"`
   `Atom`                            | string        | `"Elixir.Atom"`
   `"str"`                           | string        | `"str"`
   `"\xFF\xFF"`                      | string        | `"\xFF\xFF"`
-  `#Msgpax.Bin<"\xFF">`             | binary        | `"\xFF"`<sup>2</sup>
+  `#Msgpax.Bin<"\xFF">`             | binary        | `"\xFF"`<sup>3</sup>
   `%{foo: "bar"}`                   | map           | `%{"foo" => "bar"}`
   `[foo: "bar"]`                    | map           | `%{"foo" => "bar"}`
   `[1, true]`                       | array         | `[1, true]`
   `#Msgpax.Ext<4, "02:12">`         | extension     | `#Msgpax.Ext<4, "02:12">`
   `#DateTime<2017-12-06 00:00:00Z>` | extension     | `#DateTime<2017-12-06 00:00:00Z>`
 
-  <sup>1</sup>NaN and ±infinity are not enabled by default. See `unpack/2` for for more information.
+  <sup>1</sup>`Msgpax.Packer` provides helper functions to facilitate the serialization of natively unsupported data types.
 
-  <sup>2</sup>To deserialize back to `Msgpax.Bin` structs see the `unpack/2` options.
+  <sup>2</sup>NaN and ±infinity are not enabled by default. See `unpack/2` for for more information.
+
+  <sup>3</sup>To deserialize back to `Msgpax.Bin` structs see the `unpack/2` options.
   """
 
   alias __MODULE__.Packer

diff --git a/lib/msgpax/packer.ex b/lib/msgpax/packer.ex
@@ -103,6 +103,24 @@ defprotocol Msgpax.Packer do
   It returns an iodata result.
   """
   def pack(term)
+
+  @doc """
+  Returns serizalied NaN in 64-bit format.
+  """
+  Kernel.def(pack_nan(), do: <<0xCB, -1::64>>)
+
+  require Bitwise
+
+  @doc """
+  Returns serizalied infinity in 64-bit format.
+  """
+  Kernel.def pack_infinity(:positive) do
+    <<0xCB, 0::1, -1::11, 0::52>>
+  end
+
+  Kernel.def pack_infinity(:negative) do
+    <<0xCB, -1::12, 0::52>>
+  end
 end
 
 defimpl Msgpax.Packer, for: Atom do

diff --git a/test/msgpax_test.exs b/test/msgpax_test.exs
@@ -122,6 +122,10 @@ defmodule MsgpaxTest do
 
       assert Msgpax.unpack(packed, nonfinite_floats: true) == {:ok, value}
     end
+
+    assert Msgpax.Packer.pack_nan() == <<203, -1::64>>
+    assert Msgpax.Packer.pack_infinity(:positive) == <<203, 0x7FF0::16, 0::48>>
+    assert Msgpax.Packer.pack_infinity(:negative) == <<203, 0xFFF0::16, 0::48>>
   end
 
   test "positive fixint" do