Fix for derivative through sincospi gives StackOverflowError (#499)

* fixed stackoverflow for sincospi (#497)

* add version checks since sincospi is only defined for Julia 1.6

* Update version check for sincospi to 1.6.0-DEV.292

Co-authored-by: Andreas Noack <andreas@noack.dk>

Co-authored-by: Andreas Noack <andreas@noack.dk>

Author: mchitre

src/dual.jl

@@ -609,6 +609,16 @@ end
     return (Dual{T}(sd, cd * partials(d)), Dual{T}(cd, -sd * partials(d)))
 end
 
+# sincospi #
+#----------#
+
+if VERSION >= v"1.6.0-DEV.292"
+    @inline function Base.sincospi(d::Dual{T}) where T
+        sd, cd = sincospi(value(d))
+        return (Dual{T}(sd, cd * π * partials(d)), Dual{T}(cd, -sd * π * partials(d)))
+    end
+end
+
 ###################
 # Pretty Printing #
 ###################

test/DualTest.jl

@@ -449,6 +449,10 @@ for N in (0,3), M in (0,4), V in (Int, Float32)
 
     @test all(map(dual_isapprox, ForwardDiff.sincos(FDNUM), (sin(FDNUM), cos(FDNUM))))
 
+    if VERSION >= v"1.6.0-DEV.292"
+        @test all(map(dual_isapprox, sincospi(FDNUM), (sinpi(FDNUM), cospi(FDNUM))))
+    end
+
     if V === Float32
         @test typeof(sqrt(FDNUM)) === typeof(FDNUM)
         @test typeof(sqrt(NESTED_FDNUM)) === typeof(NESTED_FDNUM)