From de57e197ad3aeeecb8798eda7922cca9a29435e2 Mon Sep 17 00:00:00 2001
From: Kurt <kaphotics@gmail.com>
Date: Sun, 10 Nov 2024 19:11:30 -0600
Subject: [PATCH] Fix gen3 reversal exploration for 50% of seeds

line 340 - variable reuse!

In looking at the emerald disassembly, when Pressure/Hustle/Vital Spirit fails, it reduces the max level of the slot by 1 so that the max level doesn't randomly appear. Essentially 50% flat for the max to appear, for varied slots, not 50% + (1/range). Thus we require a separate branch of logic to check for this scenario.

https://github.com/pret/pokeemerald/blob/f8119bedd4eae6aa614e7378f78d548e4f721d52/src/wild_encounter.c#L298

DPPt (and assumedly HGSS) do not decrease the random range on failure.

ty TFS for bringing this to my attention on discord
---
 .../Legality/RNG/ClassicEra/Gen3/MethodH.cs   | 39 +++++++++++++++++--
 1 file changed, 36 insertions(+), 3 deletions(-)

diff --git a/PKHeX.Core/Legality/RNG/ClassicEra/Gen3/MethodH.cs b/PKHeX.Core/Legality/RNG/ClassicEra/Gen3/MethodH.cs
index eb54e5e4e..c80f52f95 100644
--- a/PKHeX.Core/Legality/RNG/ClassicEra/Gen3/MethodH.cs
+++ b/PKHeX.Core/Legality/RNG/ClassicEra/Gen3/MethodH.cs
@@ -337,9 +337,9 @@ public static class MethodH
         if (syncProc)
         {
             var ctx = new FrameCheckDetails<T>(enc, seed, levelMin, levelMax, format);
-            if (IsSlotValidRegular(ctx, out seed))
+            if (IsSlotValidRegular(ctx, out var regular))
             {
-                result = new(seed, Synchronize);
+                result = new(regular, Synchronize);
                 return true;
             }
         }
@@ -421,7 +421,9 @@ public static class MethodH
         if (IsHustleVitalPass(ctx.Prev1)) // should have triggered
         { result = default; return false; }
 
-        return IsSlotValidFrom1Skip(ctx, out result);
+        // When it fails, level range is reduced by 1 so that it is not the maximum level, if possible.
+
+        return IsSlotValidFrom1SkipMinus1(ctx, out result);
     }
 
     private static bool TryGetMatchNoSync<T>(in FrameCheckDetails<T> ctx, out LeadSeed result)
@@ -467,6 +469,21 @@ public static class MethodH
         result = default; return false;
     }
 
+    private static bool IsSlotValidFrom1SkipMinus1<T>(FrameCheckDetails<T> ctx, out uint result)
+        where T : IEncounterSlot3
+    {
+        // -3 ESV
+        // -2 Level (range biased down by 1)
+        // -1 (Proc Already Checked)
+        //  0 Nature
+        if (IsLevelValidMinus1(ctx.Encounter, ctx.LevelMin, ctx.LevelMax, ctx.Format, ctx.Prev2))
+        {
+            if (IsSlotValid(ctx.Encounter, ctx.Prev3))
+            { result = ctx.Seed4; return true; }
+        }
+        result = default; return false;
+    }
+
     private static bool IsSlotValidRegular<T>(in FrameCheckDetails<T> ctx, out uint result)
         where T : IEncounterSlot3
     {
@@ -571,6 +588,22 @@ public static class MethodH
         return (u16LevelRand % mod) + min;
     }
 
+    private static bool IsLevelValidMinus1<T>(T enc, byte min, byte max, byte format, uint u16LevelRand) where T : ILevelRange
+    {
+        var level = GetExpectedLevelMinus1(enc, u16LevelRand);
+        return IsOriginalLevelValid(min, max, format, level);
+    }
+
+    private static uint GetExpectedLevelMinus1<T>(T enc, uint u16LevelRand) where T : ILevelRange
+    {
+        var min = enc.LevelMin;
+        uint mod = 1u + enc.LevelMax - min;
+        var bias = (u16LevelRand % mod);
+        if (bias != 0)
+            bias--;
+        return min + bias;
+    }
+
     private static bool IsRockSmashPossible(byte areaRate, ref uint seed)
     {
         if (IsRatePass(seed, areaRate, None)) // Lead doesn't matter, doesn't influence.