# Random Number Generators

**TL;DR:** Use `PRNG.Instance` for 10-15x faster random generation than `UnityEngine.Random`, with a rich API for vectors, colors, weighted selection, and more.

---

## Overview

Unity Helpers provides 15+ high-performance pseudo-random number generators (PRNGs) through a unified `IRandom` interface. All generators pass standard statistical tests and are optimized for game development workloads.

### Key Features

- **10-15x faster** than `UnityEngine.Random` (see [benchmarks](../../performance/random-performance.md))
- **Thread-safe** access via `PRNG.Instance` (thread-local)
- **Rich API** — vectors, colors, Gaussian distributions, weighted selection, subset sampling
- **Seedable** — reproducible results for replays and testing
- **IL2CPP compatible** — no reflection, AOT-safe

---

## Quick Start (60 Seconds)

```csharp
using WallstopStudios.UnityHelpers.Core.Random;

// Use the thread-local default (fastest)
IRandom random = PRNG.Instance;

// Basic generation
int number = random.Next(0, 100);           // [0, 100)
float value = random.NextFloat();            // [0.0, 1.0)
bool coinFlip = random.NextBool();
uint bits = random.NextUint();

// Unity vectors
Vector2 point2D = random.NextVector2(-10f, 10f);

// Colors
Color randomColor = random.NextColor();

// Weighted selection
string[] items = { "Common", "Rare", "Epic" };
float[] weights = { 70f, 25f, 5f };
string selected = random.NextWeighted(items.Zip(weights, (x, y) => (x, y)));

// Gaussian distribution
float normalValue = random.NextGaussian(mean: 0f, stdDev: 1f);
```

---

## Choosing a Generator

| Use Case                    | Recommended Generator | Why                                            |
| --------------------------- | --------------------- | ---------------------------------------------- |
| **General gameplay**        | `PRNG.Instance`       | Thread-local default, excellent quality        |
| **Procedural generation**   | `PcgRandom`           | Reproducible, excellent statistical properties |
| **High-throughput effects** | `SplitMix64`          | Fastest with good quality                      |
| **Cryptographic seeding**   | N/A                   | Use `System.Security.Cryptography` instead     |
| **Legacy compatibility**    | `UnityRandom`         | Matches `UnityEngine.Random` behavior          |

---

## Available Generators

All generators implement the `IRandom` interface:

| Generator                     | Speed     | Quality   | Best For                           |
| ----------------------------- | --------- | --------- | ---------------------------------- |
| `LinearCongruentialGenerator` | Fastest   | Poor      | Non-critical effects only          |
| `SplitMix64`                  | Very Fast | Very Good | High-throughput generation         |
| `PcgRandom`                   | Fast      | Excellent | General purpose, seeded generation |
| `IllusionFlow`                | Fast      | Excellent | Balanced speed and quality         |
| `XoroShiroRandom`             | Fast      | Very Good | Game logic, physics                |
| `RomuDuo`                     | Fast      | Very Good | Alternative to PCG                 |
| `XorShiftRandom`              | Moderate  | Fair      | Legacy compatibility               |
| `WyRandom`                    | Moderate  | Very Good | Hash-based scenarios               |
| `SquirrelRandom`              | Moderate  | Good      | Noise-based generation             |
| `PhotonSpinRandom`            | Slow      | Excellent | Maximum quality needed             |
| `UnityRandom`                 | Slow      | Fair      | Match Unity behavior               |
| `SystemRandom`                | Very Slow | Poor      | .NET compatibility                 |

For detailed benchmarks, see [Random Performance](../../performance/random-performance.md).

---

## Creating Seeded Generators

For reproducible sequences (replays, procedural generation, testing):

```csharp
using WallstopStudios.UnityHelpers.Core.Random;

// Create with specific seed
PcgRandom seeded = new PcgRandom(seed: 12345);

// Generate reproducible sequence
for (int i = 0; i < 10; i++)
{
    Debug.Log(seeded.Next(0, 100)); // Same values every run
}

// Different seed = different sequence
PcgRandom different = new PcgRandom(seed: 67890);
```

---

## API Reference

### Basic Generation

```csharp
IRandom random = PRNG.Instance;

// Integers
int value = random.Next();                    // [int.MinValue, int.MaxValue]
int bounded = random.Next(100);               // [0, 100)
int ranged = random.Next(10, 50);             // [10, 50)

// Unsigned integers
uint bits = random.NextUint();
uint boundedUint = random.NextUint(1000u);

// Floating point
float f = random.NextFloat();                 // [0.0, 1.0)
float rangedF = random.NextFloat(-1f, 1f);    // [-1.0, 1.0)
double d = random.NextDouble();               // [0.0, 1.0)

// Boolean
bool b = random.NextBool();                   // 50% true/false
bool weighted = random.NextBool(0.75f);       // 75% true
```

### Vector Generation

```csharp
// 2D vectors
Vector2 v2 = random.NextVector2();                      // Each component [0, 1)
Vector2 ranged2 = random.NextVector2(-10f, 10f);        // Each component [-10, 10)

// 3D vectors
Vector3 v3 = random.NextVector3();
Vector3 ranged3 = random.NextVector3(-5f, 5f);
```

### Color Generation

```csharp
// Random colors
Color c = random.NextColor();                           // Random RGBA
```

### Distributions

```csharp
// Gaussian (normal) distribution
float gaussian = random.NextGaussian(mean: 0f, stdDev: 1f);

// Weighted selection
string[] items = { "Common", "Rare", "Epic", "Legendary" };
float[] weights = { 60f, 25f, 12f, 3f };
string drop = random.NextWeighted(items.Zip(weights, (x, y) => (x, y)));
```

### Collection Operations

```csharp
// Shuffle in place
myList.Shuffle(random);

// Random element
T element = random.NextOf(array);
T element2 = random.NextOf(list);

// Random index
int index = random.Next(collection.Count);
```

---

## Thread Safety

`PRNG.Instance` provides thread-local instances, making it safe for multithreaded code without locks:

```csharp
// Safe - each thread gets its own instance
Parallel.For(0, 1000, i =>
{
    int value = PRNG.Instance.Next(0, 100);
    // No race conditions
});
```

For explicit thread-local control:

```csharp
using WallstopStudios.UnityHelpers.Core.Random;

// Create thread-local wrapper around any generator
ThreadLocalRandom<PcgRandom> threadLocal = new();
IRandom random = threadLocal.Value; // Per-thread instance
```

---

## Perlin Noise

For procedural generation, use the seedable Perlin noise generator:

```csharp
using WallstopStudios.UnityHelpers.Core.Random;

PerlinNoise noise = new PerlinNoise(seed: 42);

// 2D noise (terrain, textures)
float value2D = noise.Noise(x, y);

// Octave noise for more detail
float octaves = noise.OctaveNoise(x, y, octaves: 4, persistence: 0.5f);
```

---

## Best Practices

1. **Use `PRNG.Instance`** for most cases — it's fast, thread-safe, and well-tested
2. **Seed generators explicitly** when reproducibility matters (replays, tests)
3. **Avoid `new` in hot paths** — cache generator instances
4. **Don't use for security** — these are PRNGs, not CSPRNGs

```csharp
// ✅ Good - cache the reference
private IRandom _random = PRNG.Instance;

void Update()
{
    float value = _random.NextFloat();
}

// ❌ Bad - creates new instance every frame
void Update()
{
    PcgRandom random = new PcgRandom(); // Allocation!
    float value = random.NextFloat();
}
```

---

## See Also

- [Random Performance Benchmarks](../../performance/random-performance.md)
- [Math & Extensions](./math-and-extensions.md)
- [README - Random Generators](../../readme.md#random-number-generators)