How does repairing work?

Question

I understand that repairing an item requires two items of the same type, and that putting them together in a crafting area will create a new item with more durability than the ones being repaired, but I'm wondering about the numbers behind the action.

Is the act of repairing items merely a convienience or is it actually beneficial to get the most out of said items.

Example: Two diamond shovels. If they have 10 uses left each, and I put them into a crafting area to repair them, do I get an item with 20 uses left, or does it actually give me MORE uses in the new item than the sum of the uses left in each damaged item?

Answer 1

You get more uses.

According to the Minecraft Wiki article on it, the formula is:

floor( Item A uses + Item B uses + (Max uses / 10) )

So not only do you save inventory space by combining ("repairing") partially used tools, you actually get more uses out of the combined tool.

Answer 2

According to Notch:

If item 1 has 10 uses left, and item 2 has 10 uses left, you'll end up with something like 25 uses in the final product.

And according to the wiki, the exact algorithm is:

floor(  Item A uses + Item B uses + (Max uses / 10)  )