From 7e716676942d3ee8f6ce06dbb2e1d8e4a4c39d02 Mon Sep 17 00:00:00 2001
From: Justin Lin <caterpillar@openhome.cc>
Date: Thu, 3 Oct 2019 15:06:55 +0800
Subject: [PATCH] extract fast fib

---
 src/__comm__/__fast_fibonacci.scad | 15 +++++++++++++++
 src/golden_spiral.scad             |  6 ++++--
 2 files changed, 19 insertions(+), 2 deletions(-)
 create mode 100644 src/__comm__/__fast_fibonacci.scad

diff --git a/src/__comm__/__fast_fibonacci.scad b/src/__comm__/__fast_fibonacci.scad
new file mode 100644
index 00000000..61ec0071
--- /dev/null
+++ b/src/__comm__/__fast_fibonacci.scad
@@ -0,0 +1,15 @@
+function __fast_fibonacci_sub(nth) = 
+    let(
+        _f = __fast_fibonacci_2_elems(floor(nth / 2)),
+        a = _f[0],
+        b = _f[1],
+        c = a * (b * 2 - a),
+        d = a * a + b * b
+    ) 
+    nth % 2 == 0 ? [c, d] : [d, c + d];
+
+function __fast_fibonacci_2_elems(nth) =
+    nth == 0 ? [0, 1] : __fast_fibonacci_sub(nth);
+    
+function __fast_fibonacci(nth) =
+    __fast_fibonacci_2_elems(nth)[0];
\ No newline at end of file
diff --git a/src/golden_spiral.scad b/src/golden_spiral.scad
index 28aa20cc..2b8ac5dd 100644
--- a/src/golden_spiral.scad
+++ b/src/golden_spiral.scad
@@ -8,6 +8,8 @@
 *
 **/ 
 
+include <__comm__/__fast_fibonacci.scad>;
+
 function _fast_fibonacci_sub(nth) = 
     let(
         _f = _fast_fibonacci_2_elems(floor(nth / 2)),
@@ -31,8 +33,8 @@ function _remove_same_pts(pts1, pts2) =
 
 function _golden_spiral_from_ls_or_eql_to(from, to, point_distance, rt_dir) = 
     let(
-        f1 = _fast_fibonacci(from),
-        f2 = _fast_fibonacci(from + 1),
+        f1 = __fast_fibonacci(from),
+        f2 = __fast_fibonacci(from + 1),
         fn = floor(f1 * 6.28312 / point_distance), 
         $fn = fn + 4 - (fn % 4),
         circle_pts = circle_path(radius = f1, n = $fn / 4 + 1),