fix(prover): Add signed to LOAD bus interaction signature

[ColoCarletti]

Aligns the LOAD bus interaction (LOAD-C9) with the spec update from #284, which added signed to the
interaction input signature.

Both sides of the BusId::Load interaction were missing the signed field:

• load.rs: Added signed to the LOAD-C9 receiver
• cpu.rs: Added signed to the CPU-CM51 sender

[github-actions]

Kimi Code Review

Review

File: prover/src/tables/cpu.rs

Line 1408-1414:

• Issue: The comment and code are updated to include a new signed flag for the LOAD operation. This is a change in the expected bus interaction structure.
• Action: Ensure that the addition of the signed flag is correctly handled in the rest of the codebase, particularly in the logic that processes these bus interactions. This includes verifying that the cols::SIGNED column is correctly defined and used elsewhere.

Line 1450-1456:

• Issue: The BusInteraction structure is updated to include a new signed flag. This change should be reflected in the corresponding logic that handles bus interactions.
• Action: Verify that the addition of the signed flag does not break existing functionality and that it is correctly integrated into the bus interaction processing logic.

File: prover/src/tables/load.rs

Line 425-431:

• Issue: Similar to cpu.rs, the comment and code are updated to include a signed flag in the LOAD operation specification.
• Action: Ensure that the addition of the signed flag is consistent with the changes made in cpu.rs and that it is correctly handled in the bus interaction processing logic.

Line 461-467:

• Issue: The BusInteraction structure is updated to include a new signed flag, similar to the changes in cpu.rs.
• Action: Verify that the addition of the signed flag is consistent with the changes made in cpu.rs and that it is correctly integrated into the bus interaction processing logic.

Conclusion

The changes in both files are consistent with each other, adding a signed flag to the LOAD operation's bus interactions. The primary concern is ensuring that these changes are correctly integrated into the rest of the codebase, particularly in the logic that processes bus interactions. No immediate security vulnerabilities or performance issues are identified based on the provided diff. However, thorough testing is recommended to ensure that the addition of the signed flag does not introduce any bugs or unexpected behavior.

---

Automated review by Kimi (Moonshot AI)

[github-actions]

Codex Code Review

No issues found in the diff. The added signed bus field is mirrored on both CPU and LOAD sides, so the arity stays consistent. I don’t see security, correctness, or performance risks introduced here.

[claude]

Code Review Summary

After reviewing this PR, I found no issues. The changes correctly implement the spec update from #284.

What this PR does:

• Adds the signed field to the LOAD bus interaction signature (LOAD-C9)
• Updates both the sender side (CPU table) and receiver side (LOAD table)
• Aligns with the spec change that added signed to the interaction input signature

Verification:

✅ Correctness: Both sides of the interaction now include the signed field as the last element
✅ Column exists: cols::SIGNED is defined in both tables (cpu.rs:112, load.rs:58)
✅ Trace generation: The signed field is correctly populated during trace generation (cpu.rs:684, load.rs:208)
✅ Element count: Updated comment correctly states 10 elements (was 9, now includes signed)
✅ Spec alignment: Matches the spec update from PR #284 which added signed to the LOAD interaction signature

The implementation is straightforward and correct.

[greptile-apps]

Greptile Overview

Greptile Summary

Added the signed field to both sides of the BusId::Load interaction, aligning with the spec update that requires sign/zero-extension information for load operations.

• cpu.rs (CPU-CM51 sender): Added signed flag as the 10th bus element using cols::SIGNED with Direct packing
• load.rs (LOAD-C9 receiver): Added signed flag as the 10th bus element using cols::SIGNED with Direct packing

Both sides now match exactly with the updated signature: LOAD[result; base_address, timestamp, read2, read4, read8, signed]. The cols::SIGNED column already exists in both tables and is populated during trace generation, so no additional changes were needed.

Confidence Score: 5/5

• This PR is safe to merge with no risk
• The changes are minimal, symmetric, and correctly implement the spec update. Both the sender and receiver sides of the bus interaction were updated identically, adding the same signed field in the same position using the same packing method. The required cols::SIGNED column already exists in both tables and is properly populated during trace generation. The updated comments accurately reflect the new 10-element signature.
• No files require special attention

Important Files Changed

Filename	Overview
prover/src/tables/cpu.rs	Added signed flag to CPU-CM51 LOAD bus sender (lines 1453-1457), aligning with spec update
prover/src/tables/load.rs	Added signed flag to LOAD-C9 bus receiver (lines 464-468), completing the bus interaction signature update

Sequence Diagram

sequenceDiagram
    participant CPU as CPU Table (cpu.rs)
    participant LoadBus as LOAD Bus
    participant LOAD as LOAD Table (load.rs)
    
    Note over CPU,LOAD: Bus Interaction Signature Update
    
    CPU->>LoadBus: Send LOAD interaction (M6/CPU-CM51)
    Note right of CPU: rvd, base_address, timestamp<br/>read2, read4, read8, signed
    Note right of CPU: Added signed flag from cols::SIGNED
    
    LoadBus->>LOAD: Receive LOAD interaction (LOAD-C9)
    Note right of LOAD: res, base_address, timestamp<br/>read2, read4, read8, signed
    Note right of LOAD: Added signed flag from cols::SIGNED
    
    Note over CPU,LOAD: Both sides aligned with spec<br/>Total bus elements: 10 (was 9)

Loading

[github-actions]

Benchmark Results for unmodified programs 🚀

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base binary_search	64.1 ± 2.4	62.1	68.1	1.00
head binary_search	67.8 ± 8.2	62.1	89.1	1.06 ± 0.13

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base bitwise_ops	65.4 ± 3.6	62.2	69.7	1.00
head bitwise_ops	66.3 ± 3.6	62.5	70.0	1.01 ± 0.08

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base fibonacci_26	67.7 ± 2.6	65.3	71.5	1.01 ± 0.05
head fibonacci_26	67.1 ± 2.3	65.6	71.5	1.00

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base hashmap	131.7 ± 2.3	129.3	135.5	1.00
head hashmap	134.1 ± 3.6	130.3	142.0	1.02 ± 0.03

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base keccak	126.8 ± 1.7	124.9	129.8	1.00
head keccak	128.9 ± 3.7	125.8	136.3	1.02 ± 0.03

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base matrix_multiply	68.7 ± 1.7	67.1	71.4	1.00
head matrix_multiply	69.1 ± 1.8	67.0	72.7	1.01 ± 0.04

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base modular_exp	66.2 ± 3.7	61.6	69.3	1.00 ± 0.13
head modular_exp	66.0 ± 7.6	61.7	85.7	1.00

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base quicksort	70.8 ± 5.6	66.0	81.6	1.05 ± 0.09
head quicksort	67.7 ± 2.4	65.6	71.2	1.00

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base sieve	70.4 ± 1.9	69.2	75.5	1.00
head sieve	73.6 ± 3.6	70.1	80.9	1.05 ± 0.06

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base sum_array	80.8 ± 2.9	77.7	86.9	1.00
head sum_array	81.0 ± 2.3	77.9	84.5	1.00 ± 0.05

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base syscall_commit	98.7 ± 4.4	95.3	106.7	1.01 ± 0.06
head syscall_commit	97.9 ± 3.2	96.0	106.8	1.00

[github-actions]

📊 Memory Profile Results

Program: loop_4096 (4097 instructions)

Metric	Value
Peak Memory	231.71 MB
Total Allocated	4251.33 MB

Peak Allocation Stack Trace:

0x559c5081c302: <dhat::Alloc as core::alloc::global::GlobalAlloc>::alloc (???:0:0)
0x559c5070afd2: stark::table::Table<F>::from_columns (???:0:0)
0x559c5070d498: stark::prover::IsStarkProver::multi_prove (???:0:0)
0x559c506b9bfe: lambda_vm_prover::tests::prove_elfs_tests::prove_and_verify_vm_minimal (???:0:0)
0x559c506c6fdb: lambda_vm_prover::tests::prove_elfs_tests::test_dhat_memory_profile (???:0:0)

ℹ️ No baseline found on main branch for comparison.

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