Dynamic (Magic Number) - Randomizing

Quoting Ronald Raygun

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I believe Kennyhubbard deserves the credit not me.

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Quoting Ronald Raygun

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Would you be so kind to either post the code or explain how it works?

Thanks,
--RR

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/**
* create a positive integer for the use as a magic number.
*
* The function takes a string as argument and calculates
* an 31 bit hash value from it. The hash does certainly not 
* have the strength of a real cryptographic hash function 
* but it should be more than sufficient for generating a
* unique ID from a string and collissions should not occur.
*
* use it in your init() function like this: 
*    magic = makeMagicNumber(IndicatorShortName() + Symbol() + Period());
*
* where name would be the name of your EA. Your EA will then
* get a unique magic number for each instrument and timeframe
* and this number will always be the same, whenever you put
* the same EA onto the same chart.
*
* Numbers generated during testing mode will differ from those
* numbers generated on a live chart.
*/
int makeMagicNumber(string key){
   int i, k;
   int h = 0;
   
   if (IsTesting()){
      key = "_" + key;
   }
   
   for (i=0; i<StringLen(key); i++){
      k = StringGetChar(key, i);
      h = h + k;
      h = bitRotate(h, 5); // rotate 5 bits
   }
   
   for (i=0; i<StringLen(key); i++){
      k = StringGetChar(key, i);
      h = h + k;
      // rotate depending on character value
      h = bitRotate(h, k & 0x0000000F);
   }
   
   // now we go backwards in our string
   for (i=StringLen(key); i>0; i--){   
      k = StringGetChar(key, i - 1);
      h = h + k;
      // rotate depending on the last 4 bits of h
      h = bitRotate(h, h & 0x0000000F); 
   }
   
   return(h & 0x7fffffff);
}

/**
* Rotate a 32 bit integer value bit-wise 
* the specified number of bits to the right.
* This function is needed for calculations
* in the hash function makeMacicNumber()
*/
int bitRotate(int value, int count){
   int i, tmp, mask;
   mask = (0x00000001 << count) - 1;
   tmp = value & mask;
   value = value >> count;
   value = value | (tmp << (32 - count));
   return(value);
}

//+------------------------------------------------------------------+
int hash_string(string s)
//+------------------------------------------------------------------+
{
  // this is the djb2 string hash algo
  int h = 5381, l = StringLen(s), i;
  for (i=0; i<l; i++) h = h * 33 + StringGetChar(s,i);
  return (h);
}

Quoting squalou

Disliked

I use a simple DJB2 hash algorithm to build 32-bits hash values out of strings.
It is used by Java compilers to build their symbol tables (so they'd better have a good one!).

Ignored

#include <[url="http://7bit.99k.org/common__functions_8mqh.html"]common_functions.mqh[/url]>


int magic;

int init() {
   magic = [url="http://7bit.99k.org/common__functions_8mqh.html#a4005e449c291909f9930354ed447d09d"]makeMagicNumber[/url](WindowExpertName() + Symbol() + Period());
}

int start() {

}

Quoting bluemele

Disliked

Dynamic (Magic Number) - Randomizing

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Quoting ecTrade

Disliked

Maybe you could tell the EA to generate a random number within a certain range, say, between 1 and 500, and tell it to look for magic numbers within that range? And, if you want to assign magic numbers to other EA's, just don't assign them within that range.

Hmm ... I think I might try that myself.

Ignored

Quoting ecTrade

Disliked

Really? I don't see it requiring more than one or two lines of code in order to generate the random number. The rest is pretty straight forward ... i.e., if(Magic>=1 && Magic<=500){ proceed ... }

Ignored

Quoting 7bit

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And how will you make sure you get the same number again after a crash/restart/recompile so that the EA can continue where it left?

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Quoting ecTrade

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It won't matter, so long as that number is in the specified range, as this is what the EA is set to look for.

As far as that's concerned, I don't see why you couldn't specify a different magic number for each trade (if you wanted to), again, so long as that number falls within the specified range.

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Quoting MaMood

Disliked

Hi,

maybe I miss something.
I'm assigning the result of GetTickCount() fct as magicnumber.
It should per definitionem be unique ...

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Quoting MaMood

Disliked

Hi,

maybe I miss something.
I'm assigning the result of GetTickCount() fct as magicnumber.
It should per definitionem be unique ...

Have not had any problems so far.
But I'm not sure if there any hidden shortcomings of this approach.

CU,
MaMood

Ignored

Quoting Tipster

Disliked

If you want to get the magic number back after a re-boot of compile of code that won't work. That's the point.

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Quoting 7bit

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Then you have to specify a range instead of a number and that range must be unique for each EA and for each instance ...

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Quote

Disliked

... and you are back at square one.

Quote

Disliked

Its even more complicated since you now have two numbers for every chart where you run an EA instead of only one.

Quote

Disliked

Generating it with a hash makes all this go away and you don't even have to think about it anymore.

Quoting ecTrade

Disliked

Makes what go away? Oh, can this hash thingy generate a random number specific to each order, and yes, recall it later?

Ignored

Quoting ecTrade

Disliked

Each instance of what? Are you referring to each individual trade or, the EA itself? Again, so long as you specify a specific range, as I am suggesting, you can vary the random number by each individual trade, and yes, recall them later.

Now, can this hash reference you are talking about do the same thing?

Ignored

int mn_base = makeMagicNumber(...) & 0xfffffffc;   // 2 lowest bits zero
int mn_type0 = mn_base;
int mn_type1 = mn_base + 1;
int mn_type2 = mn_base + 2;
int mn_type3 = mn_base + 3;