3 carpets not enough to smelt one item in smoker or blast furnace

Can confirm in 21w10a. Video attached.

Can confirm in 1.17.

Can confirm in 1.17.1.

I am able to confirm this behavior in 21w43a. Here are some extra details regarding this problem.

The Bug:

Three carpets aren't enough to smelt a singular item in smokers or blast furnaces.

Steps to Reproduce:

• Place down a smoker or blast furnace and obtain three carpets.

• Open the smoker/blast furnace and place the three carpets in the fuel slot.

• Obtain any smeltable item and begin smelting it.

• Take note as to whether or not three carpets are enough to smelt a singular item in smokers or blast furnaces.

Observed Behavior:

Three carpets aren't enough to smelt a singular item in smokers or blast furnaces.

Expected Behavior:

Three carpets would be enough to smelt a singular item in smokers and blast furnaces, just like how they are in regular furnaces.

I can confirm this behavior in both 1.17.1 and 1.18 Pre-release 8.

Here's a code analysis of this issue. All of the following is based on a decompiled version of Minecraft 1.17.1 using MCP-Reborn. Please note that I'm quite tentative about this analysis, although I'm persuaded to believe that this is likely a cause of the problem. 🙂

net.minecraft.world.level.block.entity.BlastFurnaceBlockEntity.java

public class BlastFurnaceBlockEntity extends AbstractFurnaceBlockEntity {
   public BlastFurnaceBlockEntity(BlockPos $$0, BlockState $$1) {
      super(BlockEntityType.BLAST_FURNACE, $$0, $$1, RecipeType.BLASTING);
   }
   ...
   protected int getBurnDuration(ItemStack $$2) {
      return super.getBurnDuration($$2) / 2;
   }
   ...

net.minecraft.world.level.block.entity.SmokerBlockEntity.java

public class SmokerBlockEntity extends AbstractFurnaceBlockEntity {
   public SmokerBlockEntity(BlockPos $$0, BlockState $$1) {
      super(BlockEntityType.SMOKER, $$0, $$1, RecipeType.SMOKING);
   }
   ...
   protected int getBurnDuration(ItemStack $$2) {
      return super.getBurnDuration($$2) / 2;
   }
   ...

If we look at the above classes, we can see that they both contain the line of code,

protected int getBurnDuration(ItemStack $$0) {
   return super.getBurnDuration($$0) / 2;
}

and as we know, this is used to increase the speed at which items are smelted at. Since both smokers and blast furnaces utilize this piece of code, it means that the burn time of fuel sources placed within them is halved.

net.minecraft.world.level.block.entity.AbstractFurnaceBlockEntity.java

public static Map<Item, Integer> getFuel() {
   Map<Item, Integer> map = Maps.newLinkedHashMap();
   ...
   add(map, ItemTags.CARPETS, 67);
   ...

Looking at the above class, we can see that the burn time of a carpet is 67 and it's important to note that this value is stored as an integer. Where this problem comes to light is when 67 is halved. When the integer 67 is divided by the integer 2, the output value is 33. If we take this knowledge and apply it with 3 carpets, we get a total burn time of 99, and with smokers and blast furnaces, at least 100 is required in order to smelt an item, therefore resulting in this issue occurring.