Touhou 14.3: Impossible Spell Card/Counterstops
About[edit | edit source]
Counterstopping (Or Overflowing) in ISC is a bug that causes the score to go to the highest possible value. It happens when the score should go negative, but since the score variable is unsigned, the code interprets it as a very big number instead (around 2.14bil), causing it to shoot to the highest value it can. The actual specifics behind what causes it to go to the highest value are based around How Numbers are Stored in a Computer.
You might be wondering how it can go to 9 billion if the interpreted value of the score is 2.14bil. This is because touhou stores its scores in two different memory addresses: One for the least significant digit (AKA the ones place) in the score, and one for the higher place values. This is because in most touhou games, the last digit of your score is how many times you've continued, and it not actually affected by anything increasing score. Any actual additions to the score are instead added to the main score variable. Since you cannot continue in ISC, this number goes unused and stays permanently at 0.
It doesn't go to 21.4bil because of ZUN hardcoding a counterstop at 9,999,999,990
In order to do this, you need to reduce your score to below zero. This is currently only possible by capturing (or timing out) a spellcard with a negative bonus. You can cause a spellcard bonus to go negative by abusing the fact that while using the camera item the timer slows down, but the spellcard bonus decrease rate does not slow. The 1st example of this to be recorded that I can find is here:
I have also created this video, which contains a helpful debrief of what the bug does in visual form at the start:
All recorded counterstops:[edit | edit source]
| Day 1 | Day 2 | Day 3 | Day 4 | Day 5 | Day 6 | Day 7 | Day 8 | Day 9 | Day 10 | |
|---|---|---|---|---|---|---|---|---|---|---|
| Scene 1 | Done | |||||||||
| Scene 2 | Done | Done | Done | Done | Done | Done | ||||
| Scene 3 | Done | Done | Done | Done | ||||||
| Scene 4 | Done | Done | Done | Done | ||||||
| Scene 5 | Done | Done | Done | Done | Done | Done | ||||
| Scene 6 | Done | Done | ||||||||
| Scene 7 | Done | |||||||||
| Scene 8 | Done | Done | ||||||||
| Scene 9 | ||||||||||
| Scene 10 |