Fix return ref to local variable in MatButterfly/MatPerm.

In tests faust_butterfly_mat.cpp.in/faust_perm_mat.cpp.in

src/faust_linear_operator/CPU/faust_MatButterfly.h

@@ -51,6 +51,7 @@ namespace Faust
 #endif
 			int level;
 			bool is_transp;
+			FPP zero;
 
 
 			public:

src/faust_linear_operator/CPU/faust_MatButterfly.hpp

@@ -7,7 +7,7 @@ namespace Faust
 	//TODO: dtor?
 
 	template<typename FPP>
-	MatButterfly<FPP, Cpu>::MatButterfly(const MatSparse<FPP, Cpu> &factor, int level)
+	MatButterfly<FPP, Cpu>::MatButterfly(const MatSparse<FPP, Cpu> &factor, int level) : zero(FPP(0))
 	{
 		// build a d1, d2 pair from the butterfly factor
 		auto size = factor.getNbRow();
@@ -71,6 +71,7 @@ namespace Faust
 #endif
 		level = src.level;
 		is_transp = src.is_transp;
+		this->zero = src.zero;
 		return *this;
 	}
 
@@ -471,11 +472,11 @@ namespace Faust
 			if(j == i - k)
 				return d2_ptr[i];
 			else
-				return FPP(0);
+				zero;
 		if(j == i + k)
 			return d2_ptr[i];
 		else
-			return FPP(0);
+			return zero;
 	}
 
 

src/faust_linear_operator/CPU/faust_MatPerm.h

@@ -45,6 +45,7 @@ namespace Faust
 			long *perm_ids_ptr;
 #endif
 			bool is_transp;
+			FPP zero;
 
 
 			public:

src/faust_linear_operator/CPU/faust_MatPerm.hpp

@@ -5,7 +5,7 @@ namespace Faust
 	//TODO: dtor?
 	//
 	template<typename FPP>
-	MatPerm<FPP, Cpu>::MatPerm()
+	MatPerm<FPP, Cpu>::MatPerm() : zero(FPP(0))
 	{
 #ifdef USE_PYTHONIC
 		perm_ids_ptr = nullptr;
@@ -441,7 +441,7 @@ namespace Faust
 		if(j == perm_ids[i])
 			return d_ptr[i];
 		else
-			return FPP(0);
+			return zero;
 	}