From d4d5ab578de59768f8a6f2b6179ec46c9968ca11 Mon Sep 17 00:00:00 2001
From: Jonathan Westhues <jwesthues@cq.cx>
Date: Wed, 2 Jul 2008 01:52:32 -0800
Subject: [PATCH] Add a special case when raising quaternions almost equal to
 (+/-1, 0, 0, 0) to some power; that was failing if the magnitude of w was
 slightly greater than 1, so that acos() returned NaN.

[git-p4: depot-paths = "//depot/solvespace/": change = 1820]
---
 util.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/util.cpp b/util.cpp
index ea9c5040..0fcaa1c4 100644
--- a/util.cpp
+++ b/util.cpp
@@ -225,6 +225,13 @@ Quaternion Quaternion::Inverse(void) {
 }
 
 Quaternion Quaternion::ToThe(double p) {
+    // Avoid division by zero, or arccos of something not in its domain
+    if(w >= (1 - 1e-6)) {
+        return From(1, 0, 0, 0);
+    } else if(w <= (-1 + 1e-6)) {
+        return From(-1, 0, 0, 0);
+    }
+
     Quaternion r;
     Vector axis = Vector::From(vx, vy, vz);
     double theta = acos(w); // okay, since magnitude is 1, so -1 <= w <= 1