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CELLSCRIPT_WIDE_VALUE_ARGUMENTS.md

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Wide value arguments and owned storage

Status: candidate implementation after 0.33.0-alpha.1; focused VM/checker regressions pass, full backend integration acceptance remains pending.

Representation

Value Internal argument Return
Primitive <=64-bit scalar One machine word a0
[u8; 1..=8] Packed word Packed a0
u128 Pointer and actual length, exactly 16 Low/high words in a0/a1
Hash, Address, ScriptHash, SighashAllDigest Pointer and actual length, exactly 32 Caller-owned hidden 32-byte destination
Fixed byte arrays of 9..=64 bytes Pointer and actual length Caller-owned hidden destination
Admitted fixed ordinary records Pointer and checked length Caller-owned hidden destination

Arguments beyond the eight register words use the aligned outgoing stack area. A hidden destination follows the ordinary words, including lengths. Nominal hash types stay distinct even when their physical widths match. These are current admitted contracts, not a promise that every larger array or dynamic value has an unrestricted direct-return ABI.

Confirmed waste and repair

U128 temporaries previously reserved 16 bytes in both the general fixed-byte bank and the U128 arithmetic bank. Read-only U128 parameters also reserved scratch that was never used. The frame planner now uses one owned buffer for each materialized value and retains the incoming pointer/length for unwritten parameters. Written parameters still receive owned storage; modifying them cannot change the caller's original or another saved copy.

The measured fixture passes five U128 arguments and returns a two-U128 record. Both versions use the same DSL source hash. All frame sizes remain 16-byte aligned; the saving removes reserved value storage rather than moving padding.

Configuration Before helper frame After helper frame Removed storage ELF bytes before/after Successful cycles before/after
Standard 1632 1456 176 5032 / 5032 7468 / 7468
Internal unoptimized diagnostics 1632 1456 176 5040 / 5040 7477 / 7477

This is a 10.8% reduction in this helper's owned frame. It is not a claim about whole-program peak stack or faster execution. Three successful vectors cover zero, upper limbs and U128::MAX; an overflowing vector must reject with the existing error. Rejected executions are not assigned a fabricated cycle cost. Machine-readable before/after observations retain the exact source hash and measurements.

Contract fixes

  • Named ScriptHash and SighashAllDigest arguments now use consistent fixed-value length slots and caller-owned results. The independent checker recognizes their 32-byte widths without treating them as ordinary Hash.
  • Computed zero-lock signing digests keep SighashAllDigest through IR and helper calls/results. Hash::from_sighash_all explicitly converts the value, and metadata retains the destination layout rather than the previous domain. SDK-oracle VM tests cover repeated returned digests and later calls.
  • Full ScriptHash .0 serialization and constant Hash/Address .0 projections agree across typing, IR, storage and independent field checks.
  • Explicit Hash::from_bytes(bytes) uses a typed constructor rather than an implicit cross-domain Move. Rebound constructors and wrong copy sources reject.
  • Branch fusion only accepts primitive scalar operands. Epoch comparisons retain fraction semantics; 1/2 == 2/4 is not decided by packed integer equality.

Verification and further opportunities

The 12 argument/result tests cover caller-owned returns, forwarding, mutable parameter isolation, fixed arrays across the 8/9-byte boundary, 32-byte nominal values, reordered record fields, large outgoing offsets, hidden stack arguments, nested calls and both return branches. Nominal-result mutations reject wrong width, wrong hidden argument, absent copies, type relabelling and bad source pointers. The collection runtime's 42 tests passed after U128 storage sharing. The complete artifact-checker integration suite also passed all 212 tests before the final browser-summary packaging refinement. Native ABI emitters and the independent checker were unchanged by that refinement.

Length descriptor elimination for internally proven fixed arguments could save ABI words. Forwarding a caller's return destination could avoid some copies. Neither change is implemented here: each needs its own source/length/alias and independent machine contract. Entry and dynamic-source length checks stay intact. The transport tests with externally supplied fixed bytes prove byte preservation, not that a transaction message was computed or authority was established. The separate signing tests compute the message and compare it with the CKB SDK. Full backend integration and clean-source acceptance are still pending.