add strptime_l comparison

DateParsingPerformanceComparison.m

#import <Foundation/Foundation.h>
#import "sqlite3.h"

typedef int64_t timestamp;

NSUInteger randomNumberInRange(NSUInteger start, NSUInteger end);

// Create a sample date using the ISO-8601 format.
// 2013-04-23T16:29:05Z
NSString* generateSampleDate();

// Create an array of <count> dates in the ISO-8601 format.
NSArray* generateSampleDates(NSUInteger count);

// Parse all given dates using SQLite's strftime function
void parseDatesUsingSQLite(NSArray *dates);

// Parse all given dates using NSDateFormatter
void parseDatesUsingNSDateFormatter(NSArray *dates);

// Parse all given dates using strptime_l
void parseDatesUsingStrptime(NSArray *dates);

static NSDateFormatter *dateFormatter = nil;

int main()
{
    @autoreleasepool
    {
        const NSUInteger count = 1000000;
        NSArray *dates = generateSampleDates(count);
        
        NSDate *start = nil;
        NSDate *end = nil;
        
        start = [NSDate date];
        parseDatesUsingStrptime(dates);
        end = [NSDate date];
        
        printf("strptime_l took %4.3f seconds\n", [end timeIntervalSinceDate:start]);
        
        start = [NSDate date];
        parseDatesUsingNSDateFormatter(dates);
        end = [NSDate date];
        
        printf("NSDateFormatter took %4.3f seconds\n", [end timeIntervalSinceDate:start]);
        
        start = [NSDate date];
        parseDatesUsingSQLite(dates);
        end = [NSDate date];
        
        printf("sqlite3 took %4.3f seconds\n", [end timeIntervalSinceDate:start]);
    }
    
    return 0;
}

NSArray* generateSampleDates(NSUInteger count)
{
    NSMutableArray *dates = [NSMutableArray array];
    
    for (int i = 0; i < count; i++)
    {
        [dates addObject:generateSampleDate()];
    }
    
    return dates;
}

NSString* generateSampleDate()
{
    NSUInteger year = randomNumberInRange(1980, 2013);
    NSUInteger month = randomNumberInRange(1, 12);
    NSUInteger date = randomNumberInRange(1, 28);
    NSUInteger hour = randomNumberInRange(0, 23);
    NSUInteger minute = randomNumberInRange(0, 59);
    NSUInteger second = randomNumberInRange(0, 59);
    
    NSString *dateString = [NSString stringWithFormat:@"%lu-%02lu-%02luT%02lu:%02lu:%02luZ",
                            year,
                            month,
                            date,
                            hour,
                            minute,
                            second
                            ];
    
    return dateString;
}

void parseDatesUsingSQLite(NSArray *dates)
{
    sqlite3 *db = NULL;
    sqlite3_open(":memory:", &db);
    
    sqlite3_stmt *statement = NULL;
    sqlite3_prepare_v2(db, "SELECT strftime('%s', ?);", -1, &statement, NULL);
    
    for (NSString *dateString in dates)
    {
        sqlite3_bind_text(statement, 1, [dateString UTF8String], -1, SQLITE_STATIC);
        sqlite3_step(statement);
        timestamp value = sqlite3_column_int64(statement, 0);
        NSDate *date = [NSDate dateWithTimeIntervalSince1970:value];
        
        sqlite3_clear_bindings(statement);
        sqlite3_reset(statement);
    }
}

void parseDatesUsingNSDateFormatter(NSArray *dates)
{
    if (dateFormatter == nil)
    {
        dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss'Z'"];
        [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
    }
    
    for (NSString *dateString in dates)
    {
        NSDate *date = [dateFormatter dateFromString:dateString];
    }
}

void parseDatesUsingStrptime(NSArray *dates)
{
    struct tm  sometime;
    const char *formatString = "%Y-%m-%dT%H:%M:%SZ";
    for (NSString *date in dates) {
        (void) strptime_l([date UTF8String], formatString, &sometime, NULL);
        NSDate *date = [NSDate dateWithTimeIntervalSince1970: timegm(&sometime)];
    }
}

NSUInteger randomNumberInRange(NSUInteger start, NSUInteger end)
{
    NSUInteger span = end - start;
    return start + arc4random_uniform(span);
}

strptime_l took 21.656 seconds
NSDateFormatter took 108.163 seconds
sqlite3 took 7.096 seconds