Question

I have a struct with 2 bytes inside. How to compute checksum (e.g. MD5 hash) for array of such structs?

public struct MyStruct
{
    public byte Byte1;
    public byte Byte2;
}

public class MyClass
{
    public static byte[] ComputeChecksum(MyStruct[] myStructs)
    {
        // TODO: calculation.
    }
}

Answer 1

So do you want STRONG digesting or just a quick error-check/consistent-lookup value?

MD5/SHA is pretty intensive operations – they’re built around block-structures that are multiples of hundreds of bytes.

fletcher and CRC32 are very efficient and do a decent job of producing a random number.. What they are not good at is having random bit positions.. So for example, you wouldn’t want a fletcher than only look at only the upper or bottom 8 bits (since there would be too little varience)..

Either find an open-source library or hit wikipedia for the various algorithms.. I tend to just use something like:

  u32 hash_mystruct(mystruct[] data, u32 count) {
      return hash((u8*)data, sizeof(mystruct) * count);
  }
  u32 hash(u8* data, u32 size) {    
    u32 hash = 19;
    for (u32 i = 0; i < size; i++) {
      u8 c = *data++;
      if (c != 0) { // usually when doing on strings this wouldn't be needed
        hash *= c;
      }
      hash += 7;
    }
  }