Index: export_stl.c
===================================================================
--- export_stl.c	(revision 35995)
+++ export_stl.c	(revision 35996)
@@ -318,6 +318,32 @@
 };
 RND_INLINE void v_transform(double dst[3], double src[3], double mx[16]);
 
+static void stl_triangle_normal(double *dx, double *dy, double *dz, double x1, double y1, double z1, double x2, double y2, double z2, double x3, double y3, double z3)
+{
+	double len;
+
+	*dx = (y2-y1)*(z3-z1) - (y3-y1)*(z2-z1);
+	*dy = (z2-z1)*(x3-x1) - (x2-x1)*(z3-z1);
+	*dz = (x2-x1)*(y3-y1) - (x3-x1)*(y2-y1);
+
+	len = sqrt((*dx) * (*dx) + (*dy) * (*dy) + (*dz) * (*dz));
+	if (len == 0) return;
+
+	*dx /= len;
+	*dy /= len;
+	*dz /= len;
+}
+
+static void stl_facet_normal(stl_facet_t *t)
+{
+	stl_triangle_normal(
+		&t->n[0], &t->n[1], &t->n[2],
+		t->vx[0], t->vy[0], t->vz[0],
+		t->vx[1], t->vy[1], t->vz[1],
+		t->vx[2], t->vy[2], t->vz[2]
+		);
+}
+
 #include "verthash.c"
 
 typedef struct {
Index: model_load_amf.c
===================================================================
--- model_load_amf.c	(revision 35995)
+++ model_load_amf.c	(revision 35996)
@@ -83,25 +83,6 @@
 	}
 }
 
-static void stl_triangle_normal(stl_facet_t *t)
-{
-	double x1 = t->vx[0], y1 = t->vy[0], z1 = t->vz[0];
-	double x2 = t->vx[1], y2 = t->vy[1], z2 = t->vz[1];
-	double x3 = t->vx[2], y3 = t->vy[2], z3 = t->vz[2];
-	double len;
-
-	t->n[0] = (y2-y1)*(z3-z1) - (y3-y1)*(z2-z1);
-	t->n[1] = (z2-z1)*(x3-x1) - (x2-x1)*(z3-z1);
-	t->n[2] = (x2-x1)*(y3-y1) - (x3-x1)*(y2-y1);
-
-	len = sqrt(t->n[0] * t->n[0] + t->n[1] * t->n[1] + t->n[2] * t->n[2]);
-	if (len == 0) return;
-
-	t->n[0] /= len;
-	t->n[1] /= len;
-	t->n[2] /= len;
-}
-
 static stl_facet_t *amf_load_volume(vtd0_t *verts, xmlNode *volume)
 {
 	xmlNode *n, *m;
@@ -135,7 +116,7 @@
 				t->vy[i] = crd[1];
 				t->vz[i] = crd[2];
 			}
-			stl_triangle_normal(t);
+			stl_facet_normal(t);
 
 			if (tail != NULL) {
 				tail->next = t;