From 24f67ffe808a41d417f7a385efef823d0930324f Mon Sep 17 00:00:00 2001
From: EnZaXD <florian.michael07@gmail.com>
Date: Tue, 20 Aug 2024 16:12:19 +0200
Subject: [PATCH] Fix compressed id overlap in legacy block item rewriter
 (#874)

---
 .../rewriters/LegacyBlockItemRewriter.java    | 21 ++++++++++++-------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/common/src/main/java/com/viaversion/viabackwards/api/rewriters/LegacyBlockItemRewriter.java b/common/src/main/java/com/viaversion/viabackwards/api/rewriters/LegacyBlockItemRewriter.java
index 32a8d08f..20d82e27 100644
--- a/common/src/main/java/com/viaversion/viabackwards/api/rewriters/LegacyBlockItemRewriter.java
+++ b/common/src/main/java/com/viaversion/viabackwards/api/rewriters/LegacyBlockItemRewriter.java
@@ -103,9 +103,9 @@ public abstract class LegacyBlockItemRewriter<C extends ClientboundPacketType, S
                 // Include data
                 short unmappedData = Short.parseShort(key.substring(dataSeparatorIndex + 1));
                 unmappedId = Integer.parseInt(key.substring(0, dataSeparatorIndex));
-                unmappedId = IdAndData.toRawData(unmappedId, unmappedData);
+                unmappedId = compress(unmappedId, unmappedData);
             } else {
-                unmappedId = IdAndData.toRawData(Integer.parseInt(key), -1);
+                unmappedId = compress(Integer.parseInt(key), -1);
             }
 
             mappings.put(unmappedId, new MappedLegacyBlockItem(id, data, name, type));
@@ -120,12 +120,12 @@ public abstract class LegacyBlockItemRewriter<C extends ClientboundPacketType, S
         // Special block color handling
         if (name != null && name.contains("%color%")) {
             for (int i = from; i <= to; i++) {
-                mappings.put(IdAndData.toRawData(i, -1), new MappedLegacyBlockItem(id, data, name.replace("%color%", BlockColors1_11_1.get(i - from)), type));
+                mappings.put(compress(i, -1), new MappedLegacyBlockItem(id, data, name.replace("%color%", BlockColors1_11_1.get(i - from)), type));
             }
         } else {
             MappedLegacyBlockItem mappedBlockItem = new MappedLegacyBlockItem(id, data, name, type);
             for (int i = from; i <= to; i++) {
-                mappings.put(IdAndData.toRawData(i, -1), mappedBlockItem);
+                mappings.put(compress(i, -1), mappedBlockItem);
             }
         }
     }
@@ -360,13 +360,13 @@ public abstract class LegacyBlockItemRewriter<C extends ClientboundPacketType, S
     }
 
     private @Nullable MappedLegacyBlockItem getMappedBlock(int id, int data) {
-        MappedLegacyBlockItem mapping = blockReplacements.get(IdAndData.toRawData(id, data));
-        return mapping != null ? mapping : blockReplacements.get(IdAndData.toRawData(id, -1));
+        MappedLegacyBlockItem mapping = blockReplacements.get(compress(id, data));
+        return mapping != null ? mapping : blockReplacements.get(compress(id, -1));
     }
 
     private @Nullable MappedLegacyBlockItem getMappedItem(int id, int data) {
-        MappedLegacyBlockItem mapping = itemReplacements.get(IdAndData.toRawData(id, data));
-        return mapping != null ? mapping : itemReplacements.get(IdAndData.toRawData(id, -1));
+        MappedLegacyBlockItem mapping = itemReplacements.get(compress(id, data));
+        return mapping != null ? mapping : itemReplacements.get(compress(id, -1));
     }
 
     private @Nullable MappedLegacyBlockItem getMappedBlock(int rawId) {
@@ -379,6 +379,11 @@ public abstract class LegacyBlockItemRewriter<C extends ClientboundPacketType, S
         return BackwardsMappingDataLoader.INSTANCE.loadFromDataDir(name);
     }
 
+    protected int compress(final int id, final int data) {
+        // Using IdAndData for the internal storage can cause id overlaps in edge cases and would lead to wrong data
+        return (id << 16) | (data & 0xFFFF);
+    }
+
     private record Pos(int x, short y, int z) {
 
         public Pos(int x, int y, int z) {