iOS BCD码、数据流、字节和MD5计算

    NSString *str = @"abc123";
    NSData *dd = [str dataUsingEncoding:NSUTF8StringEncoding];
    NSLog(@"%@",dd); // dd = <61626331 3233>

    Byte bb[] = {97,98,99,49,50,51};
    NSData *dd = [[NSData alloc]initWithBytes:bb length:6];
    NSLog(@"%@",dd);  // dd = <61626331 3233>　　　打印的结果和字符串转换是一样的

    //数据流转字节
    Byte *bb = (Byte *)[dd bytes];

    NSString *bcdstr = @"616263313233";
    int leng = (int)bcdstr.length/2;
    if (bcdstr.length%2 == 1) //判断奇偶数
    {
        leng +=1;
    }
    Byte bbte[leng];
    for (int i = 0; i<leng-1; i++)
    {
        bbte[i] = (int)strtoul([[bcdstr substringWithRange:NSMakeRange(i*2, 2)]UTF8String], 0, 16);
    }
    if (bcdstr.length%2 == 1)
    {
        bbte[leng-1] = (int)strtoul([[bcdstr substringWithRange:NSMakeRange((leng - 1)*2, 1)]UTF8String], 0, 16) *16;
    }else
    {
        bbte[leng-1] = (int)strtoul([[bcdstr substringWithRange:NSMakeRange((leng - 1)*2, 2)]UTF8String], 0, 16);
    }
    NSData *de = [[NSData alloc]initWithBytes:bbte length:leng];
    NSLog(@"%@",de); //<61626331 3233>

+(NSString *)md5HexDigest:(NSString *)str
{
    const char *original_str = [str UTF8String];
    unsigned char result[CC_MD5_DIGEST_LENGTH]; //16
    CC_MD5(original_str, (int)strlen(original_str), result);
    NSMutableString *hash = [NSMutableString string];
    for (int i = 0; i < 16; i++)
    {
        [hash appendFormat:@"%02x", result[i]];//两位表示 不足两位补0
    }
    return [hash lowercaseString];
}

+(NSString*)getMD5WithData:(NSData *)data
{
    //不要把数据流先转成char，不然如果遇到00字节就不会计算00后面数据
    unsigned char result[16]; 
    CC_MD5([data bytes], (int)[data length], result);
    NSMutableString *hash = [NSMutableString string];
    for (int i = 0; i < 16; i++)
    {
        [hash appendFormat:@"%02x", result[i]];//x就是小写的字母，X就是大写的字母，2个字节不足补0
    }
    return hash;
}