Is there a built-in lua hashing function?

[Sgraffite]

I was wondering if MicroMacro/lua has an included hashing function akin to MD5, SHA1, etc? Or do I need to get a 3rd party library to do it?

[Administrator]

No, Lua does not natively have any sort of hashing function. For what purpose do you need it?

Typically, there's two types of hashing that are commonly used. One is generating a random hash to be used in place of a password (For, say, a login mechanism. You wouldn't want to store an actual password on the client side, so a server-generated random hash is fine). The other is when hashing a string always generates the same result.

A random generated hash can be made like this:

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-- Generates a random hash with the specified length.
-- If length is less than or equal to zero, or unspecified, 32 bytes will be assumed.
function random_hash(len)
  if( len == nil or len <= 0 ) then len = 32; end;
  local holder = ""; -- a string for holding our hash temporarily


  -- create an array of all acceptable characters that can be put in our hash.
  hash_chars = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E",
                "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T",
                "U", "V", "W", "X", "Y", "Z"};

  for i = 1, len do
    local index = math.random(1, #hash_chars);
    holder = holder .. hash_chars[index];
  end

  return holder;
end

Then use it like this:

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printf("Hash: %s", random_hash(16));

To generate a 16 byte random hash.


Now, the later type of hash also has two parts: reversible and one-way. A "reversible hash" would be more like an encryption or compression type function, where a one-way hash is like MD5. MicroMacro has a Rijndael encryption algorithm in it that could be used to create a reversible hash. As long as they don't have the key to it, it would not entirely be reversible.

[Sgraffite]

I was going to make a sort of pixel checksum to make sure I know if I ever switch targets, so the hash does not need to be reversible. Similar to getPixelChecksum() in autoit. I may not need this if target id stays the same after a character is killed and ressed repeatedly, but I have not tested that yet.

Basically I set it up where I have 3 healers, all who res a single level 1 char which I kill over and over. The problem arises when the character I'm killing gets disconnected as I will then auto-target and being slaughtering off the healers, which I don't want because then I have to run them all back.

So to prevent this I need a way that stops the script if the target ever changes.

[Administrator]

Essentially, you would be converting your bytes back into a 4-byte integer. That can be done pretty simply with math. Typically, the order is RGBA, but since we don't need the Alpha channel, we'll just kind of ignore it.

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function getPixelInt(hdc, x, y)
  local r, g, b = getPixel(hdc, x, y);
  local retval = (r * 256 * 256) + (g * 256) + b;
  return retval;
end

The reason I chose to return the three color channels as opposed to a single integer color value is because of slight variations. It's simple to set an allowed range for red to be +-10 on a red variable, however, it's not so easy to do if it's a single integer. I'd still suggest doing something like this instead:

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-- returns true if the two colors are within 'delta' variation
-- else, returns false
function compareColors(r1, g1, b1, r2, g2, b2, delta)
  -- if delta was not set, set it to 10.
  if( delta == nil ) then delta = 10; end;

  if( math.abs(r2 - r1) <= delta and
      math.abs(g2 - g1) <= delta and
      math.abs(b2 - b2) <= delta )
    return true;
  else
    return false;
end