monte-carlo

pi_solver — Monte Carlo estimation of PI via named pipe

Project structure

pi_solver/          ← Rust project (EXE)
  src/main.rs
  Cargo.toml

vba/
  pi_solver.bas     ← VBA module for Excel

Building the Rust EXE

# Requires Rust (rustup.rs) and MSVC toolchain
cd pi_solver
cargo build --release

# EXE will be at:
# pi_solver\target\release\pi_solver.exe

Installing in Excel

1. Create a new workbook and save as .xlsm (macro-enabled)
2. Alt+F11 → Insert → Module
3. Paste the contents of vba/pi_solver.bas
4. Copy pi_solver.exe to the same folder as the .xlsm file
5. Run macro RunSolver (Alt+F8 → RunSolver → Run)

Named pipe protocol

Pipe: \\.\pipe\pi_solver_progress

All messages are UTF-8 strings terminated with \n:

Message	Format
Progress	PROGRESS|<sec>|<iterations>|<pi_estimate>|<error>
Done	DONE|<iterations>|<final_estimate>
Error	ERROR|<text>

EXE parameters

pi_solver.exe [seconds]

• no arguments — runs for 60 seconds
• pi_solver.exe 30 — runs for 30 seconds

How it works

Excel (VBA)                    pi_solver.exe
    │                               │
    │── Shell "pi_solver.exe" ─────►│ CreateNamedPipe
    │                               │ ConnectNamedPipe (waits)
    │── CreateFile (open pipe) ────►│ (client connected)
    │                               │
    │◄── PROGRESS|1|500000|3.14...  │ every second
    │◄── PROGRESS|2|1000000|3.141.. │
    │    ...                        │
    │◄── DONE|30000000|3.1415926..  │
    │                               │
    │ CloseHandle                   │ CloseHandle

Sheet1 cells

Cell	Content
A1/B1	Status
A2/B2	Time (seconds)
A3/B3	Iteration count
A4/B4	Current PI estimate (10 decimal places)
A5/B5	Error
A6/B6	Path to pi_solver.exe