Cesarus85--mjolnir-vr/docs/object_matching_logs/libcmt_fp8_obj.md

libs/libcmt/fp8.obj exact-match ledger

This atomic lane starts from campaign commit a34f4dde. At lane start the object was MISSING, absent from config/parked.json, absent from every Git ref and worktree, and explicitly cleared by the other active agents. The January split target exists at index 758.

Plain-English behavior

The single routine restores the x87 floating-point unit's ordinary 53-bit precision mode. It asks _controlfp to replace only the precision-control bits, leaving exception masks, rounding mode, and every unrelated control bit alone. The function does not return a value and owns no runtime data.

Provenance and target inventory

The XDK 3911 libcmt.lib used for provenance has SHA-256 60aa4c87c97eeb6662b31d9d37cf3caba1afabaec72c47b090e7a0ce8b632f55. Its obj\i386\fp8.obj member has SHA-256 b7edcb09ad051d4b628a4ee9ff82417715a1183b2830c1e7be0f2885d2f2e8e2, records source path d:\xbox-finalfre\private\sdktools\crt\crtw32\startup\i386\fp8.c, compiler identifier 0x001c2426, C line records for source lines 15 through 17, and the external C function _setdefaultprecision. This is direct provenance for ordinary CRT C, not a vendor-assembly unit.

The January target and the XDK member's runtime function already pass section_infos_equal against each other:

• padded size 0x12/0x12;
• one IMAGE_REL_I386_REL32 relocation at +0x0b to _controlfp, addend 0;
• normalized SHA-256 96e189a2020338ed95a992bce139d8b47a57ad9595a36b473c14a11cad4f7745;
• external COMDAT owner _setdefaultprecision, pick-no-duplicates, one-byte alignment;
• no January-owned .rdata, .data, or .bss.

The code bytes push 0x00030000, push 0x00010000, call _controlfp, pop the two cdecl arguments, and return. XDK Float.h identifies the constants as _MCW_PC (precision-control mask) and _PC_53 (53-bit precision), proving the readable call _controlfp(_PC_53, _MCW_PC) rather than unexplained magic numbers.

Experiment matrix

ID	Source shape	Size T/B	Relocs T/B	Base hash	First divergence	Siblings	Decision
E01	Direct void wrapper calling _controlfp(_PC_53, _MCW_PC)	0x12/0x12	1/1	96e189a20203...	none	1/1 exact	accepted: strict exact on first build

No alternative spelling is warranted unless E01 fails: the archive member, target bytes, target relocation, and XDK constant declarations already agree on the exact operation. Any failed shape will be reverted and measured here.

Strict verification

The production build uses XDK 3911 CL 13.00.9254.1 with the configured libcmt flags /O1 /Gy /I"xbox/include". The first build passes strict whole- object comparison: 0x12/0x12 bytes, 1/1 relocation at +0x0b to _controlfp with addend zero, matching COMDAT ownership/selection/alignment, and normalized SHA-256 96e189a2020338ed95a992bce139d8b47a57ad9595a36b473c14a11cad4f7745. There are no aliases and no target-owned runtime data sections. Candidate .drectve, .debug$S, and .debug$F are ordinary compiler metadata rather than runtime ownership. A clean forced rebuild produces the same strict hash, size, relocation, and ownership result.

Both halobetacache_build and libcmt_build pass. progress reports 308/833 objects overall, 267/468 Halo objects, and 41/212 libcmt objects; the current tree has 35/476 exact libcmt functions and 2,252/55,015 exact libcmt code bytes. Against the lane baseline this object contributes one function and 18 bytes; concurrent completed-object admissions account for the other movement visible in the aggregate report. The semantic audit scans 412 units, accepts 3,388 exact functions, and reports zero unit errors. All 179 project tooling tests pass. The committed per-unit regression snapshot/check passes with _setdefaultprecision still exact and no failures or warnings.

House/Berth and bug audit

The routine is direct readable C; its no-argument void is on its own line, and the void routine ends with an explicit return;. Both arguments are named, typed, and vertically formatted. It contains no assembly, volatile, forced inlining, undefined behavior, byte patch, opaque cast, raw offset, alignment override, flag change, or comparator exception. The precision reset is intended CRT behavior, not an original bug, so no bug/fix annotation is needed.