don't attempt to normalize the rotation vector

indeed, by construction of the rotation matrix, it is
guaranteed to have a length of 1.

moreover, the normalization code was missing a square-root,
fortunatelly, since the length is 1, this didn't cause any
damage (since sqrt(1) = 1).

Change-Id: I9facd668caaf5bb3bfccb139ab872f2bb2066365

1 files changed, 6 insertions, 4 deletions

diff --git a/services/sensorservice/RotationVectorSensor.cpp b/services/sensorservice/RotationVectorSensor.cpp
index 6f4b8be45fde..eecf260a7724 100644
--- a/services/sensorservice/RotationVectorSensor.cpp
+++ b/services/sensorservice/RotationVectorSensor.cpp
@@ -114,10 +114,12 @@ bool RotationVectorSensor::process(sensors_event_t* outEvent,
         float qx = sqrtf( clamp( Hx - My - Az + 1) * 0.25f );
         float qy = sqrtf( clamp(-Hx + My - Az + 1) * 0.25f );
         float qz = sqrtf( clamp(-Hx - My + Az + 1) * 0.25f );
-        const float n = 1.0f / (qw*qw + qx*qx + qy*qy + qz*qz);
-        qx = copysignf(qx, Ay - Mz) * n;
-        qy = copysignf(qy, Hz - Ax) * n;
-        qz = copysignf(qz, Mx - Hy) * n;
+        qx = copysignf(qx, Ay - Mz);
+        qy = copysignf(qy, Hz - Ax);
+        qz = copysignf(qz, Mx - Hy);
+
+        // this quaternion is guaranteed to be normalized, by construction
+        // of the rotation matrix.
 
         *outEvent = event;
         outEvent->data[0] = qx;