From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Fri, 15 Jun 2018 00:30:32 -0400
Subject: [PATCH] Configurable Alternative LootPool Luck Formula

Rewrites the Vanilla luck application formula so that luck can be
applied to items that do not have any quality defined.

See: https://luckformula.emc.gs for data and details
-----------

The rough summary is:
My goal was that in a pool, when luck was applied, the pool
rebalances so the percentages for bigger items is
lowered and smaller items is boosted.

Do this by boosting and then reducing the weight value,
so that larger numbers are penalized more than smaller numbers.
resulting in a larger reduction of entries for more common
items than the reduction on small weights,
giving smaller weights more of a chance

-----------

This work kind of obsoletes quality, but quality would be useful
for 2 items with same weight that you want luck to impact
in varying directions.

Fishing still falls into that as the weights are closer, so luck
will invalidate junk more.

This change will result in some major changes to fishing formulas.

-----------

I would love to see this change in Vanilla, so Mojang please pull :)

diff --git a/src/main/java/net/minecraft/world/level/storage/loot/entries/LootPoolSingletonContainer.java b/src/main/java/net/minecraft/world/level/storage/loot/entries/LootPoolSingletonContainer.java
index 7a52d03c488fb1e277228914b810e2d6e02beaef..4fbb0f7fefcb383c25c1c4df2e788d9a153ae376 100644
--- a/src/main/java/net/minecraft/world/level/storage/loot/entries/LootPoolSingletonContainer.java
+++ b/src/main/java/net/minecraft/world/level/storage/loot/entries/LootPoolSingletonContainer.java
@@ -122,9 +122,35 @@ public abstract class LootPoolSingletonContainer extends LootPoolEntryContainer
     protected abstract class EntryBase implements LootPoolEntry {
         @Override
         public int getWeight(float luck) {
-            return Math.max(Mth.floor((float)LootPoolSingletonContainer.this.weight + (float)LootPoolSingletonContainer.this.quality * luck), 0);
+            // Paper start - Offer an alternative loot formula to refactor how luck bonus applies
+            // SEE: https://luckformula.emc.gs for details and data
+            if (LootPoolSingletonContainer.this.lastLuck != null && LootPoolSingletonContainer.this.lastLuck == luck) {
+                return lastWeight;
+            }
+            // This is vanilla
+            float qualityModifer = (float) LootPoolSingletonContainer.this.quality * luck;
+            double baseWeight = (LootPoolSingletonContainer.this.weight + qualityModifer);
+            if (io.papermc.paper.configuration.GlobalConfiguration.get().misc.useAlternativeLuckFormula) {
+                // Random boost to avoid losing precision in the final int cast on return
+                final int weightBoost = 100;
+                baseWeight *= weightBoost;
+                // If we have vanilla 1, bump that down to 0 so nothing is is impacted
+                // vanilla 3 = 300, 200 basis = impact 2%
+                // =($B2*(($B2-100)/100/100))
+                double impacted = baseWeight * ((baseWeight - weightBoost) / weightBoost / 100);
+                // =($B$7/100)
+                float luckModifier = Math.min(100, luck * 10) / 100;
+                // =B2 - (C2 *($B$7/100))
+                baseWeight = Math.ceil(baseWeight - (impacted * luckModifier));
+            }
+            LootPoolSingletonContainer.this.lastLuck = luck;
+            LootPoolSingletonContainer.this.lastWeight = (int) Math.max(Math.floor(baseWeight), 0);
+            return lastWeight;
         }
     }
+    private Float lastLuck = null;
+    private int lastWeight = 0;
+    // Paper end
 
     @FunctionalInterface
     protected interface EntryConstructor {