So... were's a unit test to make sure this never happens again?

I rather actually see a real comment if there is no time to create a unit test.

Why does changing ZQ_PEDERSEN to ZQ_WILLIAMSON fix the bug?

Having meaningful named constants would make much more sense.

Edit: On full view of the code, the bug could be avoid if they broke out the if <demoninationX> blocks into their own function, and to prevent "typo" errors, it would be good to have a local variable named current_demoniation = demoniationX, and then reference that local variable instead of referencing the constant everytime.

Apparently those are names for 50 and 100 BTC.

From this presentation[1] or the source code[2]:

    1 Lovelace = 1 Bitcoin
    1 Goldwasser = 10 Bitcoin
    1 Rackoff = 25 Bitcoin
    1 Pedersen = 50 Bitcoin
    1 Williamson = 100 Bitcoin

But yes, those are meaningless names in themselves. Metric prefixes like "hectobitcoin" would be better.

[1]: https://sar.informatik.hu-berlin.de/teaching/2013-w/2013-w%2... [2]: https://github.com/Zerocoin/libzerocoin/blob/master/Coin.h#L...

Actually I think this might have been the fix.

https://github.com/zcoinofficial/zcoin/commit/584e1c60617d59...

Nope this -- 4 commits later, and 12 minutes ago at this time.

https://github.com/zcoinofficial/zcoin/commit/b20c177032de3c...

Looks like they replaced a 50 with a 100.