Espresso Logic Minimizer

Rust bindings to the Espresso heuristic logic minimiser from UC Berkeley, with a modern high-level API for Boolean function minimisation.

Overview

Espresso takes Boolean functions and produces minimal or near-minimal equivalent representations. This Rust crate provides safe, thread-safe bindings with modern features:

• High-Level API - Boolean expressions and truth tables (covers) with automatic dimension tracking
• Automatic Minimisation - Heuristic and exact algorithms
• Multi-Output Support - Minimise multiple outputs simultaneously
• Thread-Safe - Safe concurrent execution
• Flexible Input - Parse expressions, build truth tables, or load PLA files

Features

• Boolean Expressions - Parse and compose expressions with the expr! macro, supporting both mathematical (*, +) and logical (&, |) notation
• Cover API - Direct truth table manipulation with automatic dimension management for precise control
• Multi-Output Functions - Minimise multiple outputs simultaneously in a single cover
• Advanced Minimisation - Both heuristic (fast, ~99% optimal) and exact (guaranteed minimal) algorithms
• Don't-Care Optimisation - FD, FR, and FDR cover types for flexible optimisation with don't-care and off-sets
• Thread-Safe - Safe concurrent execution with C11 thread-local storage
• PLA File Support - Read and write Berkeley PLA format for interoperability

Quick Start

Add to your Cargo.toml:

[dependencies]
espresso-logic = "3.1"

Boolean Expression Minimisation

use espresso_logic::{BoolExpr, expr};

fn main() -> std::io::Result<()> {
    // Build expression with redundant terms
    let redundant = expr!("a" * "b" + "a" * "b" * "c");
    println!("Original: {}", redundant);
    
    // Minimise it
    let minimised = redundant.minimize()?;
    println!("Minimised: {}", minimised);  // Output: a * b
    
    Ok(())
}

Truth Table Minimisation (Cover API)

use espresso_logic::{Cover, CoverType};

fn main() -> std::io::Result<()> {
    // Create a cover for XOR function
    let mut cover = Cover::new(CoverType::F);
    
    // Add cubes: output is 1 when inputs differ
    cover.add_cube(&[Some(false), Some(true)], &[Some(true)])?;  // 01 -> 1
    cover.add_cube(&[Some(true), Some(false)], &[Some(true)])?;  // 10 -> 1
    
    let minimised = cover.minimize()?;
    println!("Minimised to {} cubes", minimised.num_cubes());
    
    Ok(())
}

Note: Covers support multi-output functions, don't-care optimisation, and PLA file I/O.

API Overview

Choose the right API for your use case:

BoolExpr - For Expression-Based Logic

Use when you need to:

• Parse or compose Boolean expressions
• Work with single-output functions
• Use high-level operators and the expr! macro

use espresso_logic::{BoolExpr, expr, Minimizable};

let xor = expr!("a" * !"b" + !"a" * "b");
let minimised = xor.minimize()?;

Cover - For Truth Tables and Multi-Output Functions

Use when you need to:

• Build truth tables directly with cubes
• Handle multi-output functions
• Control don't-care and off-sets (FD, FR, FDR types)
• Read/write PLA files

use espresso_logic::{Cover, CoverType};

let mut cover = Cover::new(CoverType::FD);  // with don't-cares
cover.add_cube(&[Some(true), None], &[Some(true)])?;  // 1- -> 1

Low-Level API - For Maximum Control

Use the espresso module directly when you need:

• Access to intermediate covers (ON-set, don't-care, OFF-set)
• Maximum performance (~5-10% faster)
• Fine-grained control over the minimisation process

See the espresso module documentation for details.

Installation

Prerequisites: Rust 1.70+, C compiler, libclang

# macOS
xcode-select --install

# Ubuntu/Debian
sudo apt-get install build-essential libclang-dev

See docs/INSTALLATION.md for detailed platform-specific instructions.

Command Line Tool

Install the optional CLI:

cargo install espresso-logic --features cli

Usage:

espresso input.pla > output.pla
espresso -s input.pla  # Show statistics

See docs/CLI.md for more options.

Examples

Run included examples:

cargo run --example boolean_expressions
cargo run --example xor_function
cargo run --example pla_file
cargo run --example concurrent_transparent

See docs/EXAMPLES.md for comprehensive code examples.

Documentation

• API Reference - Complete API documentation
• Examples Guide - Comprehensive usage examples
• Boolean Expressions - Expression API details
• PLA Format - PLA file format specification
• CLI Guide - Command-line usage
• Installation - Platform-specific setup

Testing

cargo test

See TESTING.md for comprehensive testing documentation.

Contributing

Contributions welcome! See CONTRIBUTING.md for guidelines.

License

This project contains three layers of licensed work:

• Original Espresso: UC Berkeley (permissive license)
• Modernized C Code: Sébastien Cottinet (MIT)
• Rust Wrapper: Marcos Sartori (MIT)

See LICENSE and ACKNOWLEDGMENTS.md for details.

Acknowledgments

Espresso was developed by Robert K. Brayton and his team at UC Berkeley. Special thanks to the original developers and Sébastien Cottinet for the modernized C version.

Citation

If you use this library in academic work, please cite:

@article{brayton1984logic,
  title={Logic minimization algorithms for VLSI synthesis},
  author={Brayton, Robert K and Hachtel, Gary D and McMullen, Curtis T and Sangiovanni-Vincentelli, Alberto L},
  journal={Kluwer Academic Publishers},
  year={1984}
}

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Made with ❤️ for the Rust and digital logic communities.