How to generate a number from 3 inputs

Question

I am trying to create a system in unity where a number is generated (with a range from 0 to 9) from 3 float inputs. This is to create a procedural game where being in the same location always gives the same output. Because of this, I don't just want to use an in-built random method, as it would give different results each time. However, I am struggling to create a method that can achieve this.

To summarise:

I want to be able to put in 3 values, e.g.:

[3.2344234, -44.33030, 0.22222]

And have the method come up with a number like:

[2]

But I don't want to use an in-built method.

This is what I have tried so far - It's a bit of a mess:

    public float randomNumber(float x, float y, float z)
    {
        float stage1 = (float)((Mathf.Sign(x + 512) / Mathf.Cos(z + 42) + Mathf.SmoothDampAngle(z,y,ref(z),x) * Mathf.Atan2(y - 15,z)) / 24 + 5 * 6)%7.2f;
        string stage2 = stage1.ToString();
        int stage3 = (int)stage2[5];
        float result = stage3;
        return result;
    }

Any suggestions to properly generate random numbers are most welcome.

Is there some reason [Random Class](https://learn.microsoft.com/en-us/dotnet/api/system.random?view=net-5.0) will not work? — JohnG, Sep 09 '21 at 02:49
If the same input should always give the same output you don't want anything random, you just need a formula so each location will be unique. — Retired Ninja, Sep 09 '21 at 02:50
What is the range of your coordinates? is 0 to 10 and integer or a float? — Retired Ninja, Sep 09 '21 at 03:08
If possible, I would like it to produce 3 integers from 0 to 9 (sorry about the 10). However, floats work to as I can always convert them. — Dpythonrobot, Sep 09 '21 at 03:10
You'll either want to encode all the interesting parameters that your procedural engine needs. Or you'll want a deterministic random number source, and use the random numbers in a deterministic order. Then you only need to encode the random seed. — Jeremy Lakeman, Sep 09 '21 at 03:26
`But I don't want to use an in-built method.` ... **why**? Is this a homework request? — derHugo, Sep 09 '21 at 14:21

AcidJunkie · Accepted Answer · 2021-09-09T11:48:01.070

If distribution is not that important, the following will do:

static int GetRandomNumber(float x, float y, float z)
{
    // convert the floats to byte arrays
    var b1 = BitConverter.GetBytes(x);
    var b2 = BitConverter.GetBytes(y);
    var b3 = BitConverter.GetBytes(z);

    // turn the byte arrays into integers
    var i1 = BitConverter.ToInt32(b1);
    var i2 = BitConverter.ToInt32(b2);
    var i3 = BitConverter.ToInt32(b3);

    // XOR the 3 integers
    var merged = i1 ^ i2 ^ i3;

    // get the positive value of the integer and do a modulo by 10
    // that will give you a value between 0 and 9
    var result = Math.Abs(merged) % 10;

    return result;
}

Same using unsafe:

static unsafe int GetRandomNumberUnsafe(float x, float y, float z)
{
    var i1 = *(int*)(&x);
    var i2 = *(int*)(&y);
    var i3 = *(int*)(&z);

    var merged = i1 ^ i2 ^ i3;

    var result = Math.Abs(merged) % 10;

    return result;
}

----- EDIT -----

Starting from .NET Core 2.2, you can also use HashCode.Combine:

static unsafe int GetRandomNumber(float x, float y, float z)
{
    var hash = HashCode.Combine(x, y, z);
    var result = Math.Abs(hash) % 10;
    return result;
}

perhaps add a hashing step in between xor and modulo 10 to fix distribution: [MD5 example](https://stackoverflow.com/questions/26870267/generate-integer-based-on-any-given-string-without-gethashcode) — Tanque, Sep 09 '21 at 07:29
When distribution is required, i'd rather take a different approach: create a byte array of 12 bytes size and copy the 3 float values into it. Use this byte array as input for the hash calculation. Reduce it to a positive 32-bit or 64-bit and from this value, do the modulo by 10 — AcidJunkie, Sep 09 '21 at 10:08
Note that Unity uses .Net Framework and `HashCode.Combine` doesn't exist there — derHugo, Sep 09 '21 at 14:25

derHugo · Answer 2 · 2021-09-09T14:58:03.467

Basically you can use

whatever hash algorithm you want that generates distributed values from the given input
use modulo on the hash in order to map it into your required range
since hashes might be negative values get the absolute value of the result

You could e.g. just do

public int randomNumber(float x, float y, float z)
{
    var hash = x.GetHashCode();
    hash = (hash * 397) ^ y.GetHashCode();
    hash = (hash * 397) ^ z.GetHashCode();
    return Mathf.Abs(hash % 10);
}

Or in newer version of Unity using .NET Framework 4.7.X you can actually use tuples and simply do e.g.

public int randomNumber(float x, float y, float z)
{
    return Mathf.Abs((x, y, z).GetHashCode() % 10);
}

Or as alternative assuming your values come from a Vector3 since you speak of a location you could also use your given Vector3 directly

public int randomNumber(Vector3 vector)
{
    return Mathf.Abs(vector.GetHashCode() % 10);
}

score 0 · Answer 3 · answered Sep 09 '21 at 06:01

Limit you map area for x, y and z axes and after that divide them to 10 as incremental numbers: For example x axis -100:100 freedom of movement. (30-(-30))/3=20 will give incremental number of x axis. Make an array of 10 imaginary boxes where different x, y and z location values will give different numbers according to your array. Your imaginary 3D object with cubes must include 10 members so 3x3x3 will give 9. Add one box(it is up to you) to one dimension and after that every increments step in one axis will change the number. If you want certain numbers will give always same result make as mod4(input_1)+mod4(input_2)+mod4(input_3)+mod2(input_1+input_2+input_3) may work. But I didn't check last formula, you should check it.

Please add further details to expand on your answer, such as working code or documentation citations. — Community, Sep 09 '21 at 07:57

How to generate a number from 3 inputs

3 Answers3