与某一个值异或校验

/**

 @param contentData 需要校验的内容
 @return 异或值
 */
- (int)contentCheckValue:(NSData *)contentData {
    Byte *testByte = (Byte *)[contentData bytes];
    int checksum = 0;
    for(int i=0; i<[contentData length]; i++) {
        checksum ^= testByte[i];
    }
    return checksum;
}

与一个固定的值(0x5A)异或

/**
 与一个固定的值异或

 @return 异或后的值
 */
- (NSData *)xor_0X5A {
    NSMutableData *data = [NSMutableData dataWithLength:1];
    uint8_t num = 0x5A;
    [data replaceBytesInRange:NSMakeRange(0, 1) withBytes:&num];
    Byte *byte1 = (Byte *)[self.copy bytes];
    Byte *byte2 = (Byte *)[data bytes];
    for(int i = 0; i < self.length; i++) {
        byte1[i] ^= byte2[0];
    }
    NSData *data1 = [[NSData alloc] initWithBytes:byte1 length:self.length];
    return data1;
}

异或校验（每一字节分别异或）

/**
 异或校验（每一字节分别异或）

 @return 校验值
 */
- (int)contentCheckValue {
    Byte *testByte = (Byte *)[self bytes];
    int checksum = 0;
    for(int i=0; i<[self length]; i++) {
        checksum ^= testByte[i];
    }
    return checksum;
}