From db5c8ff0ab824ba4b8bcd6cdb0b349a8e10399f4 Mon Sep 17 00:00:00 2001
From: Moelf <jerryling315@gmail.com>
Date: Thu, 9 May 2019 10:57:02 -0700
Subject: [PATCH] add mod2pi and its test

---
 src/rules.jl     | 1 +
 test/runtests.jl | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/src/rules.jl b/src/rules.jl
index 5ed0ca8..e2c9c19 100644
--- a/src/rules.jl
+++ b/src/rules.jl
@@ -58,6 +58,7 @@
 @define_diffrule Base.acsch(x)                = :( -inv(abs($x) * sqrt(1 + $x^2))      )
 @define_diffrule Base.acoth(x)                = :(  inv(1 - $x^2)                      )
 @define_diffrule Base.deg2rad(x)              = :(  π / 180                            )
+@define_diffrule Base.mod2pi(x)               = :(  isinteger($x / 2pi) ? NaN : 1      )
 @define_diffrule Base.rad2deg(x)              = :(  180 / π                            )
 if VERSION < v"0.7-"
     @define_diffrule Base.gamma(x)            = :(  digamma($x) * gamma($x)            )
diff --git a/test/runtests.jl b/test/runtests.jl
index 51455db..ede8617 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -27,6 +27,11 @@ for (M, f, arity) in DiffRules.diffrules()
         @eval begin
             goo = rand() + $modifier
             @test isapprox($deriv, finitediff($M.$f, goo), rtol=0.05)
+            # test for 2pi functions
+            if "mod2pi" == string($M.$f)
+                goo = 4pi + $modifier
+                @test NaN === $deriv
+            end
         end
     elseif arity == 2
         @test DiffRules.hasdiffrule(M, f, 2)