iOS BCD码、数据流、字节和MD5计算

一、各个之间的相互转换

1、字符串转数据流NSData

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

  通过打印转换后的数据流可以看到，数据流里是两位一个字节存储字符串ASCII码的十六进制，a = 97 = 0x61,  1 = 49 = 0x31

2、字节与数据流转换

    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];

3、根据需要直接变成NSData，倒过来同理NSData转字符串也是先变成字节在转字符串

    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>

 4、十六进制转成ASCII

//十六进制转ASCII  31 = 1  44 = D
-(NSString *)stringFromHexString:(NSString *)hexString
{
    char *myBuffer = (char *)malloc((int)[hexString length] / 2 + 1);
    bzero(myBuffer, [hexString length] / 2 + 1);
    for (int i = 0; i < [hexString length] - 1; i += 2) {
        unsigned int anInt;
        NSString * hexCharStr = [hexString substringWithRange:NSMakeRange(i, 2)];
        NSScanner * scanner = [[NSScanner alloc] initWithString:hexCharStr] ;
        [scanner scanHexInt:&anInt];
        myBuffer[i / 2] = (char)anInt;
    }
    NSString *unicodeString = [NSString stringWithCString:myBuffer encoding:4];
    return unicodeString;
}

二、MD5计算

1、字符串的MD5计算

+(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];
}

 2、字符串的MD5计算

+(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;
}

三、CRC16验证计算（需要一个头文件）

+(NSData *)crc16Digest:(NSData *)data
{
    Byte *bs = (Byte *)[data bytes];
    int len = (int)data.length;
    unsigned char acc[len];
    
    for (int i = 0; i<len; i++)
    {
        acc[i] =bs[i];
    }
    unsigned short intup = CRC16(acc, len); //调用这个要导入1个头文件
    NSString *str = [[NSString alloc]initWithFormat:@"%x",intup];
    int b = 4-(int)str.length;
    NSString *ss=[NSString new];
    for (int i =0; i<b; i++){
        ss = [NSString stringWithFormat:@"0%@",ss];
    }
    ss = [NSString stringWithFormat:@"%@%@",ss,str];
    //高低位转换
    NSString *stra = [ss substringToIndex:2];
    NSString *end = [ss substringFromIndex:2];
    NSString *yy = [NSString stringWithFormat:@"%@%@",end,stra];
    NSData *rrdata = [SingMent transcodebcd:yy];
    return rrdata;
}