Add constraints to examples in dapps/ needed to prevent overflow. #443
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Not to be merged; this is for discussion purposes.
zenhack
commented
May 27, 2022
| let coinFlip = (wagerAmount : UInt256, escrowAmount : UInt256) | ||
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| // required to ensure that the withdraw! statements do not overflow. | ||
| | (wagerAmount / 2) < MaxUInt256 - escrowAmount |
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Note that I'm not 100% sure this constraint is correct -- there might be an off by one or something here, and I'm too tired to think through this methodically. But if it's wrong, the solver should complain that it still can't be sure there's no overflow.
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@marcinjangrzybowski asked me to come up with some examples of what index type constraints would look like in glow. This PR is a first step; it adds annotations that would become necessary for our existing apps in
dapps/to type check (and adds comments explaining what's going on). I'm pleased to see that it's already catching real bugs (if ones that are unlikely to come up in practice).I'm going to mark this as a draft; we should not merge this, but it seemed like an easy way to get the diff in front of your eyes.
I plan to also look up some representative overflow exploits to see how this would apply to those as well.