make multiplication of polynomials type stable (#387)

Author: ranocha

src/contrib.jl

@@ -4,14 +4,11 @@ using Base.Cartesian
 
 
 # direct version (do not check if threshold is satisfied)
-@generated function fastconv(E::Array{T,N}, k::Array{T,N}) where {T,N}
-    quote
-        retsize = [size(E)...] + [size(k)...] .- 1
-        retsize = tuple(retsize...)
-        ret = zeros(T, retsize)
-        convn!(ret, E, k)
-        return ret
-    end
+function fastconv(E::Array{T,N}, k::Array{T,N}) where {T,N}
+    retsize = ntuple(n -> size(E, n) + size(k, n) - 1, Val{N}())
+    ret = zeros(T, retsize)
+    convn!(ret, E, k)
+    return ret
 end
 
 # in place helper operation to speedup memory allocations

test/StandardBasis.jl

@@ -408,6 +408,14 @@ end
         @test pNULL^3 == pNULL
         @test pNULL * pNULL == pNULL
 
+        if P === Polynomial
+            # type stability of multiplication
+            @inferred 10 * pNULL
+            @inferred 10 * p0
+            @inferred p2 * p2
+            @inferred p2 * p2
+        end
+
         @test pNULL + 2 == p0 + 2 == 2 + p0 == P([2])
         @test p2 - 2 == -2 + p2 == P([-1,1])
         @test 2 - p2 == P([1,-1])