iPhone App floating point calculations when released to the app store.

Question

I released my first solo iPhone app last week that calculates 12V Marine and Boat Battery usage. I had tested it vigorously on the simulator and on my iPhone, and when I was comfortable all was well, I archived the app and released it to Apple. When users started using the app, they noted a calculation was not working as expected. The below code, which is a method on a NSManagedObject model, was producing a DIFFERENT output when released to when in debug.

The below should sum up the total of the related Discharge items - but if there are no BBDischarge items, then it should return zero. Instead, when there are no items (thus the for loop doesn't fire) it returns a figure that is the direct product of the domesticAH (an NSNumber). If I set the domesticAH to 100, the below dischargeAH returns 8, if set the domesticAH to 1000, it returns 83 (the float is rounded when it is displayed). Again, I stress the below works fine when running on the simulator, or put directly onto my iPhone 4s, only once released through the app store does it screw up.

//Other dynamics hidden for simplicity
@dynamic domesticAH;
@dynamic voltage;
@dynamic profileDischarge;

-(NSNumber*) dischargeAmpH
{

    float totalWattsPD;

    //Calculate the watts per day so we can accurately calculate the percentage of each item line
    for(BBDischarge* currentDischarge in self.profileDischarge)
    {
        float totalWatt = [currentDischarge.wattage floatValue] ;
        float totalMinsPD = [currentDischarge.minutesPD floatValue]/60;
        float totaltimesUsed = [currentDischarge.timesUsed floatValue];
        float numberInOperation = [currentDischarge.number floatValue];
        totalWattsPD = totalWattsPD + ((totalWatt * totalMinsPD) * (totaltimesUsed * numberInOperation));
    }

    int voltage = ([self.voltage integerValue] + 1) * 12;

    float totalAmpsPD = totalWattsPD / voltage;

    return [NSNumber numberWithFloat:totalAmpsPD];

}

As you can see, self.domesticAH is not featured in the method anywhere, and as I can't recreate this in the simulator, I am having a hard time tracking this down.

A few questions:

• Can I debug the live version of my app? Attach XCode to my running, App Store downloaded instance of my app?
• Is there a way I can simulate an install from the archive - would anyone recommend ad hoc distribution to do this? I havent used ad hoc yet.
• Any other ideas why this might be behaving in this way?

Answer 1

Is more a hint than an answer.. but, as I already said in comments: you can check the different behavior between Release and Debug version.

This different "behavior" has been seen in the past. Is given by "Optmization Level" setting. Debug version is set to None [-O0], while the Release version is set to Fastest, Smallest [-Os].

An example here .. here another ..