Benchmark average time of [array firstObject] calls and [array lastObject] calls. Result - Sim: No difference, iPad 2: 0.9% - 2.1% in favour of firstObject

BenchmarkArray_firstObject_lastObject.m

//
//  ViewController.m
//  testDispatchBenchmark
//
//  Created by Doron Adler on 7/11/14.
//

#import "ViewController.h"
#include <mach/mach.h>
#include <mach/mach_time.h>

@implementation ViewController

typedef struct _t_pair_avg_elapsed_nano
{
    uint64_t t_0_avg_elapsed_nano;
    uint64_t t_1_avg_elapsed_nano;
}t_pair_avg_elapsed_nano, *t_pair_avg_elapsed_nano_ptr;

- (t_pair_avg_elapsed_nano) performBenchmarkIterations:(size_t)iterations{
 
    t_pair_avg_elapsed_nano result = {0,0};
    static mach_timebase_info_data_t    sTimebaseInfo;
    
    if ( sTimebaseInfo.denom == 0 ) {
        (void) mach_timebase_info(&sTimebaseInfo);
    }
    
    NSArray *array = @[@0, @1, @2, @3, @4, @5, @6, @7, @8, @9];
    
    /////// firstObject
    uint64_t t_0 = mach_absolute_time();
    for (size_t i = 0 ; i < iterations; i++) {
        NSNumber *firstObject = nil;
        firstObject = [array firstObject];
    }
    result.t_0_avg_elapsed_nano = ((mach_absolute_time() - t_0) * sTimebaseInfo.numer) / sTimebaseInfo.denom;
    result.t_0_avg_elapsed_nano /= iterations;
    
    
    /////// lastObject
    uint64_t t_1 = mach_absolute_time();
    for (size_t i = 0 ; i < iterations; i++) {
        NSNumber *lastObject = nil;
        lastObject = [array lastObject];
    }
    result.t_1_avg_elapsed_nano = ((mach_absolute_time() - t_1) * sTimebaseInfo.numer) / sTimebaseInfo.denom;
    result.t_1_avg_elapsed_nano /= iterations;
    
    return result;
}

- (IBAction) performBenchmark:(id)sender{
    
    static size_t numberOfTests            = 100000;
    static size_t iterationsPerTest        = 1000;
    
    __block uint64_t t_0_total_elapsed_nano = 0;
    __block uint64_t t_1_total_elapsed_nano = 0;
    
    dispatch_queue_t backgroundQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);
    dispatch_async(backgroundQueue, ^{
        for (size_t i = 0 ; i < numberOfTests; i++) {
            @autoreleasepool {
                t_pair_avg_elapsed_nano testResult;
                testResult = [self performBenchmarkIterations:iterationsPerTest];
                t_0_total_elapsed_nano += testResult.t_0_avg_elapsed_nano;
                t_1_total_elapsed_nano += testResult.t_1_avg_elapsed_nano;
            }
        }
        
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"The results for %zu tests with %zu iterations each are:", numberOfTests, iterationsPerTest);    //TODO: Add drum roll :p
            NSLog(@"[array firstObject] - Each call took an avg of %llu ns to run", (t_0_total_elapsed_nano / numberOfTests));
            NSLog(@"[array lastObject]  - Each call took an avg of %llu ns to run", (t_1_total_elapsed_nano / numberOfTests));
        });
    });
}

@end