另一个Delphi到Java移植问题

Question

我正在将用Delphi编写的旧应用程序移植到Java中.我在使用此函数时遇到了一些麻烦,它会计算传输消息的CRC.

这是原始代码:

       if(ReceivedMessage[slot].Message[1] = $FD) and
          (ReceivedMessage[slot].MessageLength in [1..16]) and
          (ReceivedMessage[slot].Message[counter] = $FF) then
       begin
        index := 2;
        ReceivedMessage[slot].DataReady := TRUE;

        for counter := 1 to ReceivedMessage[slot].MessageLength do
        begin
          Inc(index);

          if ReceivedMessage[slot].Message[index] < $F8 then
            ReceivedMessage[slot].Data[counter] := ReceivedMessage[slot].Message[index]
          else
          if ReceivedMessage[slot].Message[index] = $F8 then
          begin
            Inc(index);

            ReceivedMessage[slot].Data[counter] := ReceivedMessage[slot].Message[index] or $F0;
          end
          else
            ReceivedMessage[slot].DataReady := FALSE;  // Invalid data
        end;

        if ReceivedMessage[slot].DataReady = TRUE then
        begin
          Inc(index);

          if ReceivedMessage[slot].Message[index] < $F8 then
            ReceivedMessage[slot].CRC := ReceivedMessage[slot].Message[index] shl 8
          else
          if ReceivedMessage[slot].Message[index] = $F8 then
          begin
            Inc(index);

            ReceivedMessage[slot].CRC := (ReceivedMessage[slot].Message[index] or $F0) shl 8;
          end;

          Inc(index);

          if ReceivedMessage[slot].Message[index] < $F8 then
            ReceivedMessage[slot].CRC := ReceivedMessage[slot].CRC or ReceivedMessage[slot].Message[index]
          else
          if ReceivedMessage[slot].Message[index] = $F8 then
          begin
            Inc(index);

            ReceivedMessage[slot].CRC := ReceivedMessage[slot].CRC or        ReceivedMessage[slot].Message[index] or $F0;
          end;

这是我的Java代码:

 if(array[1]==0xFD && (array[2]>0 && array[2]<17) && array[pos]==(byte)0xFF)
 {
index=2;
for(int counter=1;counter<splMsg.nbytes+1;counter++)
{
     index++;
 if(array[index]<0xF8)
     data[counter]=array[index];
 else
     if(array[index]==0xF8)
     {
      index++;
      data[counter]=(byte)(array[index] | 0xF0);
     }
     else
         return 0xFC; 
}


index++;
short crc=0x0000;

if(array[index]<0xF8)
     crc=(short) (array[index]<<8);
else
   if(array[index]==0xF8)
   {
    index++;
    crc=(short)((array[index] | 0xF0) << 8);
   }
index++;
if(array[index]<0xF8)
    crc=(short) (crc | array[index]);
else
   if(array[index]==0xF8)
   {
    index++;
    crc=(short)(crc | array[index] | 0xF0);
   }

msgcrc=new byte[] {(byte)(crc >> 8 & 0xff),(byte)(crc & 0xff)};

我的函数大多数时间返回传输的CRC代码,但有时会失败并返回消息的最后两个字节.消息的最后3个字节是CRC码(2字节)和消息结束0xff字节.

有帮助吗？

谢谢,佩德罗

Answer 1

记得:

Java字节已签名.所以:

byte test = (byte)255;
System.out.println(test);

将输出: -1

和

    byte test = (byte)255;
    System.out.println(test == 255);

会打印false,但是

    byte test = (byte)255;
    System.out.println((test & 255) == 255);

将做我认为你想要实现的(在这种情况下打印true).

要使用无符号(字节)值(array[index] & 255).

您将不得不在任何地方使用0xff进行屏蔽,否则您将获得大于127的字节值的符号扩展整数.

对于比较你也可以总是做一个演员byte(例如if(test == (byte)255)),但我认为应该坚持一次转换,所以我建议你去& 0xff掩饰.