fastperm 1.0.2

A dead-simple, extreme fast permission flag system for Rust with no dependencies.
Documentation 
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// Copyright 2022 pan93412
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
//
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0

//! # FastPerm
//! 
//! A dead-simple, extreme fast permission flag system for Rust.
//! 
//! ## Usage
//! 
//! ```
//! use fastperm::{add, rm, check};
//! 
//! // Add a flag to a permission digit.
//! assert_eq!(add(0, 1), 2);
//! // Remove a flag from a permission digit.
//! assert_eq!(rm(2, 1), 0);
//! // Check if a flag is in a permission digit.
//! assert!(check(2, 1));
//! ```
//! 
//! ## Credit
//! 
//! - <https://www.xiebruce.top/1772.html>

/// Add a permission flag `n` to a permission digit `perm`
/// 
/// # Example
/// 
/// ```
/// # use fastperm::add;
/// assert_eq!(add(0, 1), 2);
/// ```
#[inline]
pub const fn add(perm: usize, n: usize) -> usize {
    perm | 1 << n
}

/// Remove a flag `n` from a permission digit `perm`.
/// 
/// # Example
/// 
/// ```
/// # use fastperm::rm;
/// assert_eq!(rm(2, 1), 0);
/// ```
#[inline]
pub const fn rm(perm: usize, n: usize) -> usize {
    perm & !(1 << n)
}

/// Check if a flag `n` is in a permission digit `perm`.
/// 
/// # Example
/// 
/// ```
/// # use fastperm::check;
/// assert!(check(2, 1));
/// assert!(!check(2, 0));
/// assert!(!check(2, 3));
/// ```
#[inline]
pub const fn check(perm: usize, n: usize) -> bool {
    (perm >> n & 1) == 1
}

#[cfg(test)]
mod tests {
    const READ: usize = 0;
    const WRITE: usize = 1;
    const EXEC: usize = 2;

    #[test]
    fn add_test() {
        assert_eq!(super::add(0, READ), 1);
        assert_eq!(super::add(0, WRITE), 2);
        assert_eq!(super::add(0, EXEC), 4);
        
        assert_eq!(super::add(1 << READ, WRITE), 3);
        assert_eq!(super::add(1 << READ, EXEC), 5);
        assert_eq!(super::add(1 << WRITE, EXEC), 6);

        assert_eq!(super::add(3, EXEC), 7);
    }

    #[test]
    fn rm_test() {
        assert_eq!(super::rm(7, EXEC), 3);

        assert_eq!(super::rm(6, EXEC), 1 << WRITE);
        assert_eq!(super::rm(5, EXEC), 1 << READ);
        assert_eq!(super::rm(3, WRITE), 1 << READ);

        assert_eq!(super::rm(4, EXEC), 0);
        assert_eq!(super::rm(2, WRITE), 0);
        assert_eq!(super::rm(1, READ), 0);
    }

    #[test]
    fn check_test() {
        assert!(super::check(7, EXEC));
        assert!(super::check(7, WRITE));
        assert!(super::check(7, READ));

        assert!(super::check(6, EXEC));
        assert!(super::check(6, WRITE));
        assert!(!super::check(6, READ));

        assert!(super::check(5, EXEC));
        assert!(!super::check(5, WRITE));
        assert!(super::check(5, READ));

        assert!(!super::check(3, EXEC));
        assert!(super::check(3, WRITE));
        assert!(super::check(3, READ));

        assert!(super::check(4, EXEC));
        assert!(!super::check(4, WRITE));
        assert!(!super::check(4, READ));

        assert!(!super::check(2, EXEC));
        assert!(super::check(2, WRITE));
        assert!(!super::check(2, READ));

        assert!(!super::check(1, EXEC));
        assert!(!super::check(1, WRITE));
        assert!(super::check(1, READ));

        assert!(!super::check(0, EXEC));
        assert!(!super::check(0, WRITE));
        assert!(!super::check(0, READ));
    }
}