ADR 0038: Scalar numeric flag state and producer ownership

Inventory counts in this record are acceptance-time historical context; the current inventory is owned by the ASL tree and its generated projections.

Historical-evidence note: test paths named below record the evidence used when this ADR was accepted; they are not active architecture or release owners. Current ownership is the four-surface ASL tree, with per-ID AVS coverage projected into spec/evidence/release-traceability-readiness.json.

Decision scope

Target production rules remain open.

Context

ADR 0089 asks for a complete scalar numeric exception contract. PTO already exposes five status bits in CORE_STATE, and the Stage 4 scalar FSU model routes profile-returned bits into that state. The target-profile decision package did not yet distinguish this closed state/lifecycle mechanism from the still-open conditions under which target arithmetic produces each flag.

The PTO ASL did not yet define a complete scalar exception-flag producer table. The missing producer conditions must remain explicit architecture gaps; tool or implementation behavior cannot silently define them.

Decision

The portable scalar exception-state mechanism is:

1. CORE_STATE[36:32] stores NV, DZ, OF, UF, and NX from low to high.
2. Reset clears all five bits.
3. A completed scalar numeric form ORs all produced bits into the old field in one update. The bits are independent and have no priority; a numeric form cannot clear an old bit.
4. A permitted full CORE_STATE system-register write replaces the field and may clear bits. This software write is distinct from numeric accumulation.
5. An illegal source type, destination type, encoding, or other rejected form faults before a flag update or profile-producer call.
6. Numeric exception outcomes do not themselves raise a synchronous PTO trap. Trap entry snapshots CORE_STATE; successful recovery restores the manager-visible ECSTATE value, including every numeric flag.

Every one of the 30 scalar FSU forms has exactly one producer owner in spec/evidence/scalar-numeric-flag-contract.json:

• FABS produces no flags.
• FMIN, FMAX, and the four quiet comparisons produce NV exactly for a signaling NaN input.
• The four signaling comparisons produce NV exactly for any NaN input.
• The other 19 forms obtain an exact five-bit vector from one named numeric- profile hook. Each supported operation/type rule must define that vector; a missing rule rejects before effects under ADR 0037.

Consequences

The flag state, lifecycle, trap envelope, and 30/30 producer-owner matrix are closed. Eleven architecture-owned forms have complete production conditions. Nineteen profile-owned forms still require exact conditions for NV, DZ, OF, UF, and NX, including simultaneous production, tininess and NX coupling, special values, conversion overflow, and rounding.

This decision does not accept ADR 0089, increment the S5-T2-A2 decision count, or establish target numeric conformance. ADR 0089 remains open until all 19 profile-owned rows have accepted operation/type rules and independent vectors. The repository maturity therefore remains M4 and S5-T2 remains open.

Evidence

• spec/evidence/scalar-numeric-flag-contract.json
• scripts/generate-scalar-numeric-flag-contract
• asl/scalar/floating.asl
• asl/scalar/dispatch.asl
• asl/profiles/pto-v0.asl
• tests/asl/scalar/model/dispatch/fsu/scalar-exec-flag-and-rounding-helpers-001.asl
• docs/status/decisions/0028-scalar-fsu-totality-and-profile-boundary.md
• spec/evidence/numeric-profile-decision-proposals.json