Performance of math functions?

Question

I'm working with graphing accelerometer data here, and I'm trying to correct for gravity. To do this, I get the acceleration vector in spherical coordinates, decrease the radius by 1g, and convert back to cartesian. This method is called on a timer every 0.03 seconds:

//poll accleration
ThreeAxisAcceleration current = self.accelerationData;

//math to correct for gravity:
float radius = sqrt(pow(current.x, 2) + pow(current.y, 2) + pow(current.z, 2));
float theta = atan2(current.y, current.x);
float phi = acos(current.z/radius);

//NSLog(@"SPHERICAL--- RADIUS: %.2f -- THETA: %.2f -- PHI: %.2f", radius, theta, phi);

radius = radius - 1.0;

float newX = radius * cos(theta) * sin(phi);
float newY = radius * sin(theta) * sin(phi);
float newZ = radius * cos(phi);

current = (ThreeAxisAcceleration){newX, newY, newZ};

//end math
NSValue *arrayVal = [NSValue value:&current withObjCType:@encode(ThreeAxisAcceleration)];

if ([_dataHistoryBuffer count] > self.bounds.size.width) {
    [_dataHistoryBuffer removeObjectAtIndex:0];
}

[_dataHistoryBuffer addObject:arrayVal];

[self setNeedsDisplay];

Somehow, the addition of the gravity correction is gradually slowing my code horrendously. I find it hard to believe that this amount of math can slow down the program, but yet without it it can still run through my entire display method which is quite lengthy. Are there any options I can consider here to avoid this? Am I missing something or is the math just that slow? I can comment out between the //math and //end math tags and be just fine.

Thanks for any help.

P.S. incase it may matter, to whom it may interest, I'm programming in cocoa, and this method belongs to a subclass of CALayer, with -drawInContext: implemented.

Answer 1

Are you on iPhone? Try using the float variants of these functions: powf, sqrtf, etc

There's more info in point #4 of Kendall Helmstetter Gelner's answer to this SO question.