✅ PROJECT COMPLETE

XyWrite III v3.58b — EDITOR3.EXE (185,138 bytes) Binary-exact reconstruction achieved.

Final Build Verification

Metric	Result	Status
File size	185,138 / 185,138	✅ MATCH
MZ header fields	14 / 14	✅ MATCH
Relocations	1,333 / 1,333	✅ MATCH
Relocation zones	58 / 58	✅ MATCH
MZ Checksum	0x5CE2	✅ MATCH
MD5	CE49205B339D1C29569A292A4CBFFE5F	✅ MATCH

This is the first bit-perfect reconstruction of XyWrite III v3.58b in history.

Build Command

mount C F:\RE\REVERSE\XyWrite\XyWrite3\build
mount D F:\RE\REVERSE\XyWrite\Tools
C:
BUILD40_364.BAT

Project Summary

Objective: Reconstruct XyWrite III Plus EDITOR3.EXE from binary disassembly into binary-accurate x86-16 assembly source code that assembles to a byte-identical executable.

Target Binary:

• File: EDITOR3.EXE (XyWrite III Plus word processor, circa 1989–1990)
• Size: 185,138 bytes
• MD5: CE49205B339D1C29569A292A4CBFFE5F
• Platform: MS-DOS, 8086/8088 real mode (16-bit)

Toolchain Used:

• Assembler: Microsoft MASM 4.0 (1985)
• Linker: Microsoft LINK 3.64.1
• Environment: DOSBox-X (host: Windows)
• Verification: PowerShell scripts on Windows

Result: Binary-identical reconstruction achieved on February 19, 2026, after 59+ working sessions spanning approximately 3 months.

Build Process

REM BUILD40_364.BAT — assembles 40 XY3_*.ASM files, links with response file
D:\MASM40\MASM XY3_XXXX.ASM,LINK3641\XY3_XXXX.OBJ,LINK3641\XY3_XXXX.LST;
D:\LINKVERS\V3.64\LINK @LINK3641.RSP

Link order is critical — controlled by LINK3641.RSP to produce correct relocation ordering. All files follow the XY3_XXXX.ASM naming convention (8.3 DOS compatible).

XYWrite3 – Refactor & Modernization TODO

Code Documentation

• Comment all assembly routines (purpose, inputs, outputs, side effects)
• Add file-level headers describing each module
• Document calling conventions used across routines
• Explain any non-obvious optimizations or low-level tricks

Code Organization

• Split large assembly files into smaller, logical modules
• Group related subroutines into dedicated files (e.g., text handling, I/O, UI)
• Standardize file naming conventions
• Ensure each file has a clear, single responsibility

Labels & Naming

• Identify all ambiguous or auto-generated labels
• Rename labels to meaningful, descriptive names
• Establish naming conventions for:
  • Functions
  • Local labels
  • Global labels
  • Constants and macros
• Remove unused or duplicate labels

Build System

• Organize build scripts for modular assembly files
• Ensure reproducible builds
• Add debug vs release build configurations
• Document build steps clearly

Code Cleanup

Testing & Validation

• Verify behavior matches original XYWrite functionality
• Create small test cases for critical routines
• Check edge cases (large files, unusual input)
• Validate stability after refactoring

Modernization Preparation

• Identify reusable algorithms and logic
• Separate platform-dependent code (DOS-specific parts)
• Mark areas for future C++/Qt reimplementation
• Define clean interfaces for porting components

Project Management

• Track progress per module
• Maintain changelog of refactors
• Set milestones for incremental cleanup

Bugs & Limitations

• Identify and document all existing bugs
• Reproduce bugs consistently with test cases
• Categorize bugs (critical, major, minor)
• Identify architectural or design limitations
• Document constraints imposed by legacy DOS environment
• Fix confirmed bugs systematically
• Refactor or redesign areas causing major limitations

Feature Planning

• Identify missing or desirable features for XYWrite3
• Prioritize features (core vs optional)
• Ensure new features align with lightweight philosophy
• Avoid feature bloat—define strict inclusion criteria
• Create a roadmap for feature implementation

Toolchain & Assembly Accuracy

• Identify the original assembler used (if possible) for XYWrite sources

• Evaluate modern compatible assemblers (MASM, TASM, NASM, FASM)

• Select the assembler that produces the most accurate binary output

• Identify and configure a compatible linker for the chosen assembler

• Ensure the build toolchain replicates original binary behavior as closely as possible

• Audit all db-encoded instruction sequences

  • Example: db 81h, 0FFh, 6, 0 → replace with cmp di, 6
  • Example: - db 32h, 0E4h → xor ah, ah - db 8Bh, 0C8h → mov cx, ax - db 36h, 29h, 0Eh, 3Ah, 37h → sub word ptr ss:[0x373a], cx - db 7Eh, 2 → jle <label> - db 0F3h, 0A4h → rep movsb - db 8Bh, 0F3h → mov si, bx

• Replace raw opcode (db) sequences with proper assembly mnemonics wherever possible

• Identify why raw opcodes were originally used:

  • Assembler limitations
  • Optimization tricks
  • Self-modifying code
  • Macro/workaround behavior

• Validate that rewritten instructions produce identical machine code

• Use disassembly tools to verify correctness of transformations

• Preserve behavior in edge cases (flags, segment overrides, etc.)

• Document any instructions that must remain as raw opcodes and explain why

• Establish guidelines for when db usage is acceptable vs prohibited

• Create automated or semi-automated process for opcode-to-mnemonic conversion (if feasible)

• Ensure final codebase is readable, maintainable, and assembler-friendly