Mjolnir IV v1.3 File Shuffle

Thank you to https://www.reddit.com/user/nclsdv/ for finding this bug!

Renames UAL folder to FusionFix
Updates Readme, Compatability, etc. for updated instructions and readability.

Mjolnir IV v1.2 - Save Fix

Fix: Stripped in-process stack sampler that was causing save failures (SuspendThread deadlock during serialization).

No gameplay changes - same CPU fixes as v1.1:

• Fix 1: CPU Core 0 affinity unpin
• Fix 2: Busywait SwitchToThread yield
• Fix 7: Auto-adjuster disable

Thank you to https://www.reddit.com/user/nclsdv/ for finding this bug!

MJOLNIR_IV — GTA IV CPU PERFORMANCE FIX v1.1

==============================================================================
MJOLNIR_IV — GTA IV CPU PERFORMANCE FIX v1.0
For GTA IV: The Complete Edition (Steam)

WHAT THIS IS

Mjolnir_IV is a runtime patch DLL that corrects three engine-level issues in
GTA IV's RAGE engine. These are not workarounds. They are direct fixes to the
engine's behavior at the instruction level.

WHAT IT FIXES

Fix 1 — CPU Core 0 Affinity Pin

GTA IV hardcodes a SetThreadAffinityMask call that locks the main engine
thread to CPU Core 0 exclusively. This was a deliberate decision in 2008
when single-core performance was the primary constraint on Xbox 360 hardware.
On modern 8-to-24-core CPUs, this creates a severe bottleneck: one core
pegged at 70-90% while every other core sits idle.

This fix removes the pin and allows the OS scheduler to distribute the
thread freely across available cores.

A/B test results (60-second samples, per-core monitoring):

Metric                  Baseline    Fixed       Delta
-------------------------------------------------------
Core 0 utilization      72.4%       28.6%       -43.8 pp
Total process CPU       17.2%       17.6%       +0.4 (noise)

Total CPU work is identical. The load redistributes. Core 0 is no longer
the single point of failure for frame delivery.

Fix 2 — Busy-Wait Spinloop Yield

The RAGE engine contains an inner coordination loop that spins continuously
without yielding between iterations with no Sleep, no SwitchToThread, no PAUSE
instruction. On 2008 dual-core CPUs this was invisible. On modern processors
with aggressive power/thermal management, this loop burns a full core
waiting for a state that could be checked at 1ms intervals with zero
perceptible latency cost.

This fix injects a SwitchToThread call into the loop via a code cave. The
thread cooperates with the Windows scheduler rather than fighting it.

Observed result: micro-tearing reduced, frame delivery noticeably
smoother across the board.

Fix 3 — Quality Auto-Adjuster Disabled

GTA IV ships a quality auto-adjuster that re-evaluates your graphics settings
at runtime and can silently downgrade them if its internal VRAM estimation
decides you are over budget. The estimation logic uses Xbox 360-era constants
and does not correctly account for modern GPU VRAM sizes. The adjuster flag
is set to inactive, giving you full manual control over your graphics settings.
The engine's VRAM detection itself works correctly on Complete Edition.

INSTALLATION

This release includes two installation methods. Choose the one that matches
your setup.

OPTION A — Vanilla (no other DLL mods)

Use this if you are running vanilla.

1. Navigate to your GTA IV installation directory
   (typically: Steam\steamapps\common\Grand Theft Auto IV\GTAIV)

2. Copy dinput8.dll from the "Vanilla" folder into that directory,
   alongside GTAIV.exe

3. Launch the game normally through Steam

4. A log file (mjolnir_cpu_fix.log) will be created in the game directory
   on first run, confirming which fixes were applied and their patch addresses.

To uninstall: delete dinput8.dll and any mjolnir_cpu_fix.log from the game
directory, verify game files.

OPTION B — Ultimate ASI Loader (recommended)

Use this if you already have Ultimate ASI Loader installed. Ultimate ASI
Loader ships as dinput8.dll in your game directory — the .asi method
avoids conflicting with it.

1. Navigate to your GTA IV installation directory
   (typically: Steam\steamapps\common\Grand Theft Auto IV\GTAIV)

2. Copy Mjolnir_IV.asi from the "Ultimate ASI Loader" folder into that
   directory, alongside GTAIV.exe

3. Launch the game normally through Steam

4. A log file (mjolnir_cpu_fix.log) will be created in the game directory
   on first run, confirming which fixes were applied and their patch addresses.

To uninstall: delete Mjolnir_IV.asi and any mjolnir_cpu_fix.log files from the game directory.

NOTE: Do NOT install both. Use either dinput8.dll (Vanilla) or
Mjolnir_IV.asi (ASI Loader), not both at the same time.

No ini configuration or other dependencies for either method.

SUPPORTED VERSIONS

Game: GTA IV Complete Edition (Steam, patch 1.2.0.59)
OS: Windows 10 / Windows 11 (x64)
CPU: Any — greatest benefit on 8+ core modern processors
GPU: Any — these fixes are CPU-side only

Not tested on: downgraded (pre-CE) exe builds, GFWL builds, or Rockstar
Games Launcher standalone installs. The patch verifies expected byte sequences
before applying and will abort with a log entry if the exe version is wrong.

LICENSE

MIT License. See LICENSE.txt.
Fix source is not published at this time.

CONTACT / UPDATES

Check the release thread for updates. Report issues with your log file attached.

==============================================================================

Version 1.1

Thank you to nclsdv for pointing this out: We had issues with saving due to ME LEAVING DEBUG TOOLS IN THE RELEASE. Huge fail. Removed those, added in proper files. Tested saving, worked!

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