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

libs/libcmt/ismbspc.obj exact-match ledger

This isolated atomic lane starts from authoritative campaign commit 0261a4b3. Configuration index 777 was MISSING; the unit was absent from config/parked.json, production history, matching logs, branches, worktrees, and every active peer claim.

Plain-English behavior

_ismbcspace answers whether one character is whitespace. Values above 255 could represent a two-byte multibyte character, but this Xbox CRT build does not classify those values here and returns false. For an ordinary byte it uses the CRT's locale-aware isspace machinery. That machinery calls _isctype when a multibyte locale is active and otherwise indexes the current byte-type table directly.

Provenance and January inventory

The exact obj\i386\ismbspc.obj member was extracted from the local XDK 3911 libcmt.lib. CodeView names the original source d:\xbox-finalfre\private\sdktools\crt\crtw32\mbstring\ismbspc.c and carries ordinary function/line records, proving compiled C rather than assembly. Microsoft's corresponding 1985-2001 source was recovered from the pinned Easy-Build-2k NT source mirror at commit 36fce23389e43918faf4cd88688c64aa2668ff8f. It confirms the one-byte guard and isspace classifier topology; the January machine code proves that this Xbox build selects the false result for values above one byte.

The authenticated archive function compares strict-equal to January before any production source is written:

• symbol: __ismbcspace
• size: 48 bytes
• relocations: 3
• normalized SHA-256: d5e4dbfe19e55cfe1d691deb199708de1e4f36a222c64fc64285311d66155b8b
• relocation identities: +0x10 -> ___mb_cur_max, +0x1B -> __isctype, and +0x24 -> __pctype

January owns one .text section and no data, BSS, or read-only data. The archive's select-any CRT build-number metadata is not owned by January and is not reproduced.

Measured source-shape experiments

All measurements use XDK 3911 CL 13.00.9254.1 under the inherited, unchanged /O1 /Gy command.

ID	Readable-C source shape	Result
E00	Natural one-byte guard using named UCHAR_MAX, with only <ctype.h> included	Compile-time rejection: this historical header does not transitively declare UCHAR_MAX. No object was produced.
E01	Add the proper <limits.h> dependency; keep if (character > UCHAR_MAX) return 0; return isspace(character);	Strict exact on the first successful build: 48/48 bytes, 3/3 relocations with identical address/type/destination/addend, and equal normalized hash. Accepted.

No alternate control-flow, declaration-order, or codegen experiment was needed. The source is the ordinary named-constant expression of the recovered Microsoft algorithm.

Original-behavior and bug audit

No original bug was found. Returning false for values above UCHAR_MAX is a deliberate contract of this Xbox build, not a truncated Unicode test: this API accepts an encoded multibyte character value, while the selected runtime path supports only the byte classifier here. The reconstruction preserves that choice exactly rather than attempting a modern Unicode interpretation.

House, Berth, and readability audit

The function is ordinary typed C with its parameter on its own line, a named standard-library bound, and explicit returns. It has no raw object/tag access, opaque offsets, invented layout, or magic classifier bit in production source; isspace exposes the intended CRT abstraction.

No assembly, volatile, forced inlining, undefined behavior, byte patch, codegen cast, compiler-flag change, alignment trick, pragma, comparator exception, or prebuilt-object substitution is used.

Final validation

• The candidate object was deleted and force-rebuilt with XDK 3911 CL 13.00.9254.1 under unchanged /O1 /Gy; the hardened comparison remained strict exact.
• Whole-object runtime ownership is exact: one 48-byte .text COMDAT, three relocations, and no data, BSS, read-only data, or unexpected external definition. Compiler directive/debug sections are not linked ownership.
• Full halobetacache_build and libcmt_build: successful.
• progress: successful; this unit contributes one function and 48 code bytes, with libcmt at 68/212 complete objects in this isolated baseline.
• semantic_progress and explicit semantic audit: zero unit errors and this function accepted by strict COFF evidence.
• Admission audit: no unmarked completion candidate or newly contradicted label. The sole shell_xbox contradiction is the known unrelated global finding.
• Tooling unit tests: 179/179 passed.
• git diff --check: clean.
• Clean per-unit regression snapshot/check: force-rebuilt the committed unit, retained __ismbcspace as still_exact, and reported no changed non-exact function, failure, or warning.