Modulo Function

Quake2Player

Hi, Can someone tell me a MODULO algorithm like google's, typical calculator's, excel's, etc? Because, they all return 0 for: 4029800 mod 100 But C# (and java I think) return -10

DaveyM69

4029800 % 100 gets 0 for me :confused:

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)
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Lost User

Quake2Player wrote:

But C# (and java I think) return -10

Could you show the code? That really isn't what should happen, not in Java either.

Dave Kreskowiak

Your code is bad somewhere. For two positive integers, modulo is never negative.

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Quake2Player

Random r = new Random(); int key = r.Next(0, 10000); int prime = r.Next(key, key * 999); int a = r.Next(1, prime - 1); int b = r.Next(0, prime - 1); Console.WriteLine(key); Console.WriteLine(prime); Console.WriteLine(a); Console.WriteLine(b); Console.WriteLine( ((key*a + b)%prime) % 1000); Console.ReadLine(); For example: In google: (((8 568 * 4 974 445) + 2 820 002) % 7 661 773) % 1 000 = 563} In c#: (((8 568 * 4 974 445) + 2 820 002) % 7 661 773) % 1 000 = -732

Luc Pattyn

Quake2Player wrote:

8 568 * 4 974 445)

using 32-bit signed arithmetic (as in int) this results in an overflow, that is where the negative stuff is coming from. Nothing wrong with the modulo operator. test: declare long variables, initialize them, and use those for your expression, instead of numeric constants. (decimal should work too). :)

Luc Pattyn

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DaveyM69

It's because of the overflow in the first part of the calculation. Make one of the values a double and you get the correct result. (((8568 * 4974445d) + 2820002) % 7661773) % 1000)

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)
Why are you using VB6? Do you hate yourself? (Christian Graus)

DaveyM69

Beat me to it! :mad: :laugh:

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)
Why are you using VB6? Do you hate yourself? (Christian Graus)

Quake2Player

THANK YOU!

Quake2Player

How can I use long if I'm generating random numbers??? This is all about the UNIVERSAL HASHING FUNCTION:

        public int Evaluate(int key) 
        {
                // Random prime bigger than 10000
                do {
                  randomPrime = rnd.Next(10001, 10000*999);
                }
                while (!IsPrime(randomPrime));

                this.randomA = rnd.Next(1, randomPrime - 1);
                this.randomB = rnd.Next(0, randomPrime - 1);

                return ((randomA * key + randomB) % randomPrime) % tableLength;
        }

Notes: -10000 is the maximum possible key -tableLength is 1000. -randomA, randomB and randomPrime are ints As Im getting negative numbers Im trying return Math.Abs(((randomA * key + randomB) % randomPrime) % tableLength); But its not giving me fast results in the hash table

modified on Saturday, August 29, 2009 6:01 PM