C++ stepwise comparison #210
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BLOCKER: Stepwise comparison currently leaks |
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This is as minimal as possible, and should be reviewed with whitespace ignored. This adds a new `EvalStep` function that contains the bulk of the interpreter, with `EvalScript`’s `while` loop calling `EvalStep`.
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Well, my _tiny_ edge case of “only if the 202nd operation is a disabled opcode” didn’t slip past the fuzzer. It caught that pretty quickly. So, this does a better job of normalizing errors for comparisons. First, it normalizes both the C++ and Rust side, which allows the Rust error cases to not be a superset of the C++ error cases. Then, it also normalizes errors in the stepwise comparator (which I think was done in ZcashFoundation#210, but it’s reasonable to do along with these other changes). Then it handles a couple “ambiguous” cases. One was already done – `UNKNOWN_ERROR` on the C++ side with `interpreter::Error::Num` on the Rust side, but now it’s handled differently. The other is the edge case I introduced earlier in this PR – Rust will fail with a `DisabledOpcode` and C++ will fail with a `OpCount`, so those two cases have been unified.
sellout
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Well, my _tiny_ edge case of “only if the 202nd operation is a disabled opcode” didn’t slip past the fuzzer. It caught that pretty quickly. So, this does a better job of normalizing errors for comparisons. First, it normalizes both the C++ and Rust side, which allows the Rust error cases to not be a superset of the C++ error cases. Then, it also normalizes errors in the stepwise comparator (which I think was done in ZcashFoundation#210, but it’s reasonable to do along with these other changes). Then it handles a couple “ambiguous” cases. One was already done – `UNKNOWN_ERROR` on the C++ side with `interpreter::Error::Num` on the Rust side, but now it’s handled differently. The other is the edge case I introduced earlier in this PR – Rust will fail with a `DisabledOpcode` and C++ will fail with a `OpCount`, so those two cases have been unified.
sellout
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May 22, 2025
Well, my _tiny_ edge case of “only if the 202nd operation is a disabled opcode” didn’t slip past the fuzzer. It caught that pretty quickly. So, this does a better job of normalizing errors for comparisons. First, it normalizes both the C++ and Rust side, which allows the Rust error cases to not be a superset of the C++ error cases. Then, it also normalizes errors in the stepwise comparator (which I think was done in ZcashFoundation#210, but it’s reasonable to do along with these other changes). Then it handles a couple “ambiguous” cases. One was already done – `UNKNOWN_ERROR` on the C++ side with `interpreter::Error::Num` on the Rust side, but now it’s handled differently. The other is the edge case I introduced earlier in this PR – Rust will fail with a `DisabledOpcode` and C++ will fail with a `OpCount`, so those two cases have been unified.
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This PR exposes stepwise evaluation on the C++ and runs it against the Rust side to ensure the state is identical every step of the way.
There are two commits here. The first one makes minimal changes to the C++ interpreter to expose an
EvalStepfunction. It should be reviewed with whitespace ignored, since the body of the interpreter is reindented without changes.The second commit implements the comparison work, changing the
zcash_script.hinterface.