Comparison of float and double pre-defined values in iOS/LLVM

floatDoubleTest.m

//
//  main.m
//  quicky
//
//  Created by Aaron Zinman on 2/21/12.
//  Copyright (c) 2012 Empirical Design LLC. All rights reserved.
//

#import <Foundation/Foundation.h>

void runTest(int numIterations);

int main (int argc, const char * argv[]) {
  for (unsigned int magnitude = 100; magnitude < INT_MAX; magnitude *= 10) {
    runTest(magnitude);
  }
  return 0;
}

void runTest(int numIterations) {
  NSTimeInterval startTime = CFAbsoluteTimeGetCurrent();
  float d = 1.2f;
  for (int i = 0; i < numIterations; i++) {
    d += 1.8368383;
    d *= 0.976;
  }
  NSTimeInterval timeWithDoubles = CFAbsoluteTimeGetCurrent() - startTime;
  
  startTime = CFAbsoluteTimeGetCurrent();
  float f = 1.2f;
  for (int i = 0; i < numIterations; i++) {
    f += 1.8368383f;
    f *= 0.976f;
  }
  NSTimeInterval timeWithFloats = CFAbsoluteTimeGetCurrent() - startTime;
  printf("\n------------ %d total loops\n", numIterations);
  printf("timeWithDoubles: %2.5f sec\n", timeWithDoubles);
  printf("timeWithFloats: %2.5f sec\n", timeWithFloats);
  printf("Float speed up: %2.2fx\n", timeWithDoubles / timeWithFloats);
  printf("Difference in calculation: %f\n", d - f);
}

/*

************* IN SIMULATOR, DEBUG ************* 

------------ 100 total loops
timeWithDoubles: 0.00000 sec
timeWithFloats: 0.00000 sec
Float speed up: 1.06x
Difference in calculation: -0.000031

------------ 1000 total loops
timeWithDoubles: 0.00001 sec
timeWithFloats: 0.00001 sec
Float speed up: 1.50x
Difference in calculation: -0.000038

------------ 10000 total loops
timeWithDoubles: 0.00012 sec
timeWithFloats: 0.00008 sec
Float speed up: 1.60x
Difference in calculation: -0.000038

------------ 100000 total loops
timeWithDoubles: 0.00123 sec
timeWithFloats: 0.00073 sec
Float speed up: 1.70x
Difference in calculation: -0.000038

------------ 1000000 total loops
timeWithDoubles: 0.01207 sec
timeWithFloats: 0.00749 sec
Float speed up: 1.61x
Difference in calculation: -0.000038

------------ 10000000 total loops
timeWithDoubles: 0.11871 sec
timeWithFloats: 0.07306 sec
Float speed up: 1.62x
Difference in calculation: -0.000038

------------ 100000000 total loops
timeWithDoubles: 1.16302 sec
timeWithFloats: 0.72541 sec
Float speed up: 1.60x
Difference in calculation: -0.000038



************* ON IPAD 1, DEBUG ************* 


------------ 100 total loops
timeWithDoubles: 0.00002 sec
timeWithFloats: 0.00001 sec
Float speed up: 1.51x
Difference in calculation: -0.000031

------------ 1000 total loops
timeWithDoubles: 0.00013 sec
timeWithFloats: 0.00008 sec
Float speed up: 1.58x
Difference in calculation: -0.000038

------------ 10000 total loops
timeWithDoubles: 0.00125 sec
timeWithFloats: 0.00079 sec
Float speed up: 1.58x
Difference in calculation: -0.000038

------------ 100000 total loops
timeWithDoubles: 0.01331 sec
timeWithFloats: 0.00800 sec
Float speed up: 1.66x
Difference in calculation: -0.000038

------------ 1000000 total loops
timeWithDoubles: 0.12797 sec
timeWithFloats: 0.08504 sec
Float speed up: 1.50x
Difference in calculation: -0.000038

------------ 10000000 total loops
timeWithDoubles: 1.33593 sec
timeWithFloats: 0.80924 sec
Float speed up: 1.65x
Difference in calculation: -0.000038


************* IN SIMULATOR, RELEASE (-O3) ************* 

------------ 100 total loops
timeWithDoubles: 0.00000 sec
timeWithFloats: 0.00000 sec
Float speed up: infx
Difference in calculation: -0.000031

------------ 1000 total loops
timeWithDoubles: 0.00001 sec
timeWithFloats: 0.00000 sec
Float speed up: 1.76x
Difference in calculation: -0.000038

------------ 10000 total loops
timeWithDoubles: 0.00008 sec
timeWithFloats: 0.00003 sec
Float speed up: 2.48x
Difference in calculation: -0.000038

------------ 100000 total loops
timeWithDoubles: 0.00077 sec
timeWithFloats: 0.00031 sec
Float speed up: 2.47x
Difference in calculation: -0.000038

------------ 1000000 total loops
timeWithDoubles: 0.00774 sec
timeWithFloats: 0.00310 sec
Float speed up: 2.49x
Difference in calculation: -0.000038

------------ 10000000 total loops
timeWithDoubles: 0.07770 sec
timeWithFloats: 0.03098 sec
Float speed up: 2.51x
Difference in calculation: -0.000038

------------ 100000000 total loops
timeWithDoubles: 0.77059 sec
timeWithFloats: 0.30755 sec
Float speed up: 2.51x
Difference in calculation: -0.000038

*/