[Bitcoin-development] Testnet3 difficulty transition problem?

[Gregory Maxwell]

On Sat, Dec 22, 2012 at 1:39 PM, Andreas Schildbach
<andreas at schildbach.de> wrote:
> Both blocks
>
> 38304 00000000015bb4069249fa1f41ae61d8a7447aaacc33c50dacd3c3654377fa43
>
> and
>
> 40320 000000008011f56b8c92ff27fb502df5723171c5374673670ef0eee3696aee6d
>
> are difficulty transition blocks. However, block 40320 has a difficulty
> of 1. I know there is this special testnet rule that allows mining a
> block at difficulty 1,

Yes.

> but I always thought you can't use this exception
> on difficulty transition blocks.

Not so— but what you're actually seeing is that difficult change is
relative to the prior block's difficulty. E.g. if the penultimate
block in the difficulty cycle is under the special rule the difficulty
change will be relative to 1.

(I had intentionally avoided triggering that test case when adding the
timewarp attack to the testnet chain in case we had wanted to fix it
prior to testnet3's release— I guess I should have added it sooner in
order to catch the bitcoinj misbehavior!)