Parse multi-byte integers from UDP data[]

Programming Questions

Ghettokon

Parse multi-byte integers from UDP data[]

in Programming Questions • 2 years ago

Hi All

Question:
What is the equivalent of C# BitConverter in Processing? If there is none, is it possible to read 4-byte integers and 2-byte integers from the data[] with Processing?

Backstory:
I am trying to read the UDP packets coming from Optitrack (industrial 3D Motion tracking system) with Processing. I learned that pocket is made of multi-byte data, such as 4-byte integers and 2-byte integers. It won't work with the UDP library examples using -> new String(data[]). I have no problem receiving data from the port, I just can't parse the data[] correctly.

Tried and not working:
1. Converting each byte to a string equivalent with char() and then concatenating.
2. add byte together based on the byte syntax (e.g byte(data[0]+data[1]) )
2. new String(data[]);

Thanks,
Kyle

Replies(5)

Ghettokon

Re: Parse multi-byte integers from UDP data[]

2 years ago

http://processing.org/discourse/yabb2/YaBB.pl?num=1115324625

I found this post seems to help this problem!

Ghettokon

Re: Parse multi-byte integers from UDP data[]

2 years ago

From the link I found the following code:

return (sendInt[0] << 24)
     | (sendInt[1] << 16)
     | (sendInt[2] << 8)
     | sendInt[3];

The explanation made perfect sense in terms of byte shifting but it didn't work out for me. In my parsing method, I want to extract 4th to7th byte out of the data[] and convert it into one int value. This what I have plus the code on top, still not working properly I suppose to get 4294967295 but I got 0 in the println instead...

void receive( byte[] data ) {
      int byteIndex = 0;
      int[] sendint = new int[data.length];

      for(int i=0; i<data.length; i++){
            sendint[i]=int(data[i]);      }

      int messageID= (sendint[7] << 24) | (sendint[6] << 16) | (sendint[5] << 8) | sendint[4];            println(messageID);
}

I tried to reverse the sendint[] order in the shift it doesn't help either...
Any hint helps! Thanks!

PhiLho

Re: Parse multi-byte integers from UDP data[]

2 years ago

Works for me. Note that this depends if data is big endian or small endian.

void setup()
{
byte[] data = { 0x01, 0x12, 0x23, 0x34, 0x45, 0x56, 0x67, 0x78 };
println(hex(get4Bytes(0, data)));
println(hex(get2Bytes(4, data)));
}
int get2Bytes(int offset, byte[] data)
{
return (data[offset + 2] << 8) |
data[offset + 3];
}
int get4Bytes(int offset, byte[] data)
{
return (data[offset] << 24) |
(data[offset + 1] << 16) |
(data[offset + 2] << 8) |
data[offset + 3];
}

Ghettokon

Re: Parse multi-byte integers from UDP data[]

2 years ago

Hi Phi

thanks so much for your replay, I was in the installation room last night and trying out the code. I am comparing the processing result with the working one I wrote in C#. For the same byte[] I got two different yet super similar numbers,

Processing: println(hex(get4Bytes(0, data))) gives me 00070000

C#: BitConverter.ToUInt32(data, 0); gives me 7

if I am doing correctly with your code ( I modified the byte2 method I think there was a typo in there ) which I think I am, how do I go from 00070000 to 7?

Thanks!
Kyle

PhiLho

Re: Parse multi-byte integers from UDP data[]

2 years ago

See if the following works on a more significant amount of test data:

int get2Bytes(int offset, byte[] data)
{
return (data[offset] << 8) |
data[offset + 1];
}
int get4Bytes(int offset, byte[] data)
{
return get2Bytes(offset, data) + (get2Bytes(offset + 2, data) << 16)
}

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