Initial commit: Theriapolis baseline at port/godot branch point

Captures the pre-Godot-port state of the codebase. This is the rollback anchor for the Godot port (M0 of theriapolis-rpg-implementation-plan-godot-port.md). All Phase 0 through Phase 6.5 work is included; Phase 7 is in flight. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-04-30 20:40:51 -07:00
commit b451f83174
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+namespace Theriapolis.Core.Util;
+
+/// <summary>
+/// SplitMix64-based pseudo-random number generator with named sub-stream support.
+/// All game randomness must go through this class — no new System.Random() anywhere.
+/// </summary>
+public sealed class SeededRng
+{
+    private ulong _state;
+
+    public SeededRng(ulong seed)
+    {
+        // Mix the seed to avoid bad low-entropy states
+        _state = seed == 0 ? 0x9e3779b97f4a7c15UL : seed;
+        // Warm up the state
+        NextUInt64();
+        NextUInt64();
+    }
+
+    /// <summary>Create a sub-stream for a specific subsystem using the world seed and a named tag constant.</summary>
+    public static SeededRng ForSubsystem(ulong worldSeed, ulong subsystemTag)
+        => new(worldSeed ^ subsystemTag);
+
+    public ulong NextUInt64()
+    {
+        // SplitMix64 step
+        _state += 0x9e3779b97f4a7c15UL;
+        ulong z = _state;
+        z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9UL;
+        z = (z ^ (z >> 27)) * 0x94d049bb133111ebUL;
+        return z ^ (z >> 31);
+    }
+
+    public uint NextUInt32() => (uint)(NextUInt64() >> 32);
+
+    /// <summary>Returns a double in [0, 1).</summary>
+    public double NextDouble() => (NextUInt64() >> 11) * (1.0 / (1UL << 53));
+
+    /// <summary>Returns a float in [0, 1).</summary>
+    public float NextFloat() => (float)NextDouble();
+
+    /// <summary>Returns a float in [min, max).</summary>
+    public float NextFloat(float min, float max) => min + NextFloat() * (max - min);
+
+    /// <summary>Returns an int in [min, max).</summary>
+    public int NextInt(int min, int max)
+    {
+        if (max <= min) return min;
+        return min + (int)(NextUInt64() % (ulong)(max - min));
+    }
+
+    /// <summary>Returns an int in [0, max).</summary>
+    public int NextInt(int max) => NextInt(0, max);
+
+    /// <summary>Returns true with probability p (0–1).</summary>
+    public bool NextBool(double p = 0.5) => NextDouble() < p;
+
+    /// <summary>Shuffles a span in place using Fisher–Yates.</summary>
+    public void Shuffle<T>(Span<T> span)
+    {
+        for (int i = span.Length - 1; i > 0; i--)
+        {
+            int j = NextInt(0, i + 1);
+            (span[i], span[j]) = (span[j], span[i]);
+        }
+    }
+}