Implement CLZ opcode

[elopez]

Description

This also bumps the Solidity version used in tests to be able to compile an example with CLZ

Checklist

• tested locally
• added automated tests
• updated the docs
• updated the changelog

[elopez]

It is worth noting that this does not implement CLZ on the SMT, help is welcome on that regard 😄

[msooseth]

OK, this should now work, but the ethereum-tests have moved, and have changed format, so that needs to be updated, as per @elopez

[msooseth]

@elopez wanna review this? I resolved the cash with main by taking the main on the flake.lock, I hope that's good? The change is: 84c1e37 Plus I added a CLZ smt implementation of course

[blishko]

Nice!
I think it looks good!
I think it would be nice to fix the one misaligned line in the SMT encoding, and add a negative test.
We can also add a concrete test!

[blishko]

Maybe we should add a negative test as well?

[msooseth]

OK, added more tests, including negative tests. I actually much prefer these to the ones that were added as part of forge, because forge tests are slower and harder to edit. But I'll leave those in, too, they do check forge which is nice.

[elopez]

@elopez wanna review this? I resolved the cash with main by taking the main on the flake.lock, I hope that's good? The change is: 84c1e37 Plus I added a CLZ smt implementation of course

IIRC the flake.lock change was upgrading the solcs.nix, but I think that might have been upgraded independently since opening this PR. As long as we have a recent enough solc that can do clz we should be ok :)

[elopez]

@msooseth can you remove tests that should pass now from the problematicTests list? It should be at least these, but possibly some other ones as well 😄 https://github.com/argotorg/hevm/blob/17e0724/test/EVM/Test/BlockchainTests.hs#L217-L221

[msooseth]

Damn. Windows is failing, maybe because of the nix "cleanup" I did:

2026-02-04T14:12:08.1858158Z     Fusaka:                                                       compilation failed: exit code: ExitFailure 1
2026-02-04T14:12:08.1859277Z 
2026-02-04T14:12:08.1859664Z stdout:
2026-02-04T14:12:08.1859843Z 
2026-02-04T14:12:08.1859850Z 
2026-02-04T14:12:08.1859968Z stderr:
2026-02-04T14:12:08.1860896Z Error: Encountered invalid solc version in src\unit-tests.t.sol: No solc version exists that matches the version requirement: ^0.8.31
2026-02-04T14:12:08.1861958Z 
2026-02-04T14:12:08.1945072Z FAIL
2026-02-04T14:12:08.1952906Z       Exception: Internal Error: Error compiling test file "test/contracts/pass/fusaka.sol" in directory "D:\\a\\_temp\\msys64\\tmp\\dapp-test-dc2ed3372c7debb4" -- CallStack (from HasCallStack):

[msooseth]

OK, moved Windows to latest solidity.

[blishko]

LGTM!