NSData CRC32 Category

NSData+CRC32.h

@interface NSData (CRC32)

-(NSUInteger) crc32;

@end

NSData+CRC32.m

#import "NSData+CRC32.h"

@implementation NSData (CRC32)

-(NSUInteger)crc32
{
    uint32_t *table = malloc(sizeof(uint32_t) * 256);
    uint32_t crc = 0xffffffff;
    uint8_t *bytes = (uint8_t *)[self bytes];
    
    for (uint32_t i=0; i<256; i++) {
        table[i] = i;
        for (int j=0; j<8; j++) {
            if (table[i] & 1) {
                table[i] = (table[i] >>= 1) ^ 0xedb88320;
            } else {
                table[i] >>= 1;
            }
        }
    }
    
    for (int i=0; i<self.length; i++) {
        crc = (crc >> 8) ^ table[crc & 0xff ^ bytes[i]];
    }
    crc ^= 0xffffffff;
    
    free(table);
    return crc;
}

@end

NSData+CRC32Tests.h

#import <SenTestingKit/SenTestingKit.h>
#import "NSData+CRC32.h"

@interface NSDataCRC32Tests : SenTestCase

@end

NSData+CRC32Tests.m

#import "NSData+CRC32Tests.h"

@implementation NSDataCRC32Tests

-(void) testNSDataCRC32
{
    // # Test data from Ruby/Zlib:
    //
    // require 'zlib'
    // Zlib::crc32('')              # => 0
    // Zlib::crc32('abc')           # => 891568578
    // Zlib::crc32('Hello, World!') # => 3964322768
    
    NSString *str;
    NSData *data;
    NSUInteger checksum, expected;
    
    str = @"";
    data = [str dataUsingEncoding:NSUTF8StringEncoding];
    checksum = [data crc32];
    expected = 0;
    STAssertEquals(checksum, expected, [NSString stringWithFormat:@"did not compute correct checksum for %@", str]);
    
    str = @"abc";
    data = [str dataUsingEncoding:NSUTF8StringEncoding];
    checksum = [data crc32];
    expected = 891568578;
    STAssertEquals(checksum, expected, [NSString stringWithFormat:@"did not compute correct checksum for %@", str]);
    
    str = @"Hello, World!";
    data = [str dataUsingEncoding:NSUTF8StringEncoding];
    checksum = [data crc32];
    expected = 3964322768;
    STAssertEquals(checksum, expected, [NSString stringWithFormat:@"did not compute correct checksum for %@", str]);
}

@end

Migrated to XCTest Framework

#import "NSData+CRC32.h"
#import <XCTest/XCTest.h>

@interface NSData_CRC32Tests : XCTestCase

@end

@implementation NSData_CRC32Tests

- (void)setUp {
    [super setUp];
    // Put setup code here. This method is called before the invocation of each test method in the class.
}

- (void)tearDown {
    // Put teardown code here. This method is called after the invocation of each test method in the class.
    [super tearDown];
}

- (void)testNSDataCRC32
{
    // # Test data from Ruby/Zlib:
    //
    // require 'zlib'
    // Zlib::crc32('')              # => 0
    // Zlib::crc32('abc')           # => 891568578
    // Zlib::crc32('Hello, World!') # => 3964322768

    NSString *str;
    NSData *data;
    NSUInteger checksum, expected;

    str = @"";
    data = [str dataUsingEncoding:NSUTF8StringEncoding];
    checksum = [data crc32];
    expected = 0;
    XCTAssertEqual(checksum, expected, @"did not compute correct checksum for %@", str);

    str = @"abc";
    data = [str dataUsingEncoding:NSUTF8StringEncoding];
    checksum = [data crc32];
    expected = 891568578;
    XCTAssertEqual(checksum, expected, @"did not compute correct checksum for %@", str);

    str = @"Hello, World!";
    data = [str dataUsingEncoding:NSUTF8StringEncoding];
    checksum = [data crc32];
    expected = 3964322768;
    XCTAssertEqual(checksum, expected, @"did not compute correct checksum for %@", str);
}