Avoided zero devision in cube root approximation

Halley's method to get a better approximation is omitted, if it
would include a devision by zero (INFINITY/NaN is worse).

Change-Id: Ida09326e2b5892d7cb21bcb956631c289e5b56ba
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 9 insertions, 5 deletions

diff --git a/tests/auto/corelib/tools/qeasingcurve/tst_qeasingcurve.cpp b/tests/auto/corelib/tools/qeasingcurve/tst_qeasingcurve.cpp
index fa747b3c18..3348b49110 100644
--- a/tests/auto/corelib/tools/qeasingcurve/tst_qeasingcurve.cpp
+++ b/tests/auto/corelib/tools/qeasingcurve/tst_qeasingcurve.cpp
@@ -730,14 +730,16 @@ double static inline _fast_cbrt(double d)
 
 void tst_QEasingCurve::testCbrtDouble()
 {
-    const qreal errorBound = 0.0001;
+    const double errorBound = 0.0001;
 
     for (int i = 0; i < 100000; i++) {
         double d = double(i) / 1000.0;
         double t = _fast_cbrt(d);
 
         const double t_cubic = t * t * t;
-        t = t * (t_cubic + d + d) / (t_cubic + t_cubic + d);
+        const double f = t_cubic + t_cubic + d;
+        if (f != 0.0)
+            t = t * (t_cubic + d + d) / f;
 
         double expected = pow(d, 1.0/3.0);
 
@@ -754,14 +756,16 @@ void tst_QEasingCurve::testCbrtDouble()
 
 void tst_QEasingCurve::testCbrtFloat()
 {
-    const qreal errorBound = 0.0005;
+    const float errorBound = 0.0005;
 
-    for (int i = 1; i < 100000; i++) {
+    for (int i = 0; i < 100000; i++) {
         float f = float(i) / 1000.0f;
         float t = _fast_cbrt(f);
 
         const float t_cubic = t * t * t;
-        t = t * (t_cubic + f + f) / (t_cubic + t_cubic + f);
+        const float fac = t_cubic + t_cubic + f;
+        if (fac != 0.0f)
+            t = t * (t_cubic + f + f) / fac;
 
         float expected = pow(f, float(1.0/3.0));