performance improved

src/util/sum.scad

@@ -9,5 +9,8 @@
 **/ 
 
 function sum(lt) = 
-    let(leng = len(lt))
+    let(
-    [for(i = 0; i < leng; i = i + 1) 1] * lt;
+        end = len(lt) - 1, 
+        cum_total = [for(i = 0, s = lt[0]; i < end; i = i + 1, s = s + lt[i]) s]
+    )
+    cum_total[len(cum_total) - 1] + lt[end];