Create SizePower9a.cs

https: //x.com/Sibuna_Switch/status/2000090054371537099
Co-Authored-By: Lusamine <30205550+Lusamine@users.noreply.github.com>

PKHeX.Core/Legality/Encounters/Templates/Gen9/SizePower9a.cs

@@ -0,0 +1,56 @@
+using System;
+using static PKHeX.Core.SizePower9a;
+
+namespace PKHeX.Core;
+
+public enum SizePower9a : byte
+{
+    Normal,
+    Teensy1,
+    Teensy2,
+    Teensy3,
+    Humungo1,
+    Humungo2,
+    Humungo3,
+}
+
+public static class SizePower9aExtensions
+{
+    /// <summary>
+    /// Gets a random size value for the specified <see cref="SizePower9a"/>.
+    /// </summary>
+    /// <param name="type">Size Type</param>
+    /// <param name="rand">RNG to generate value with.</param>
+    /// <returns>Size Value</returns>
+    /// <exception cref="ArgumentOutOfRangeException"></exception>
+    public static byte GetSizeValue(this SizePower9a type, ref Xoroshiro128Plus rand) => type switch
+    {
+        Normal => (byte)(rand.NextInt(0x81) + rand.NextInt(0x80)), // triangular distribution
+        Teensy1 => (byte)rand.NextInt(128),
+        Teensy2 => (byte)rand.NextInt(96),
+        Teensy3 => (byte)rand.NextInt(32),
+        Humungo1 => (byte)(rand.NextInt(128) + 128),
+        Humungo2 => (byte)(rand.NextInt(96) + 160),
+        Humungo3 => (byte)(rand.NextInt(32) + 224),
+        _ => throw new ArgumentOutOfRangeException(nameof(type), type, null),
+    };
+
+    /// <summary>
+    /// Checks if the specified value is within the range of the <see cref="SizePower9a"/>.
+    /// </summary>
+    /// <param name="type">Size Type</param>
+    /// <param name="value">Value to check</param>
+    /// <returns>True if the value is within the range of the <see cref="SizePower9a"/>.</returns>
+    /// <exception cref="ArgumentOutOfRangeException"></exception>
+    public static bool IsWithinRange(this SizePower9a type, byte value) => type switch
+    {
+        Normal => true,
+        Teensy1 => value < 128,
+        Teensy2 => value < 96,
+        Teensy3 => value < 32,
+        Humungo1 => value >= 128,
+        Humungo2 => value >= 160,
+        Humungo3 => value >= 224,
+        _ => throw new ArgumentOutOfRangeException(nameof(type), type, null),
+    };
+}