//! An implementation of a trait describing valid skipfield integer types.
//!
//! Only `u16`s and `u8`s are supported by default. However, other integral
//! types may be used by implementing this trait on them; the trait is not
//! sealed.

use core::ops::{Add, AddAssign, Sub, SubAssign};

/// Trait describing integral types in a generic way suitable for use as the
/// element type of a skipfield.
pub trait SkipfieldType:
    Add + AddAssign + Sub + SubAssign + Ord + PartialOrd + Copy + Sized
{
    /// The maximum attainable value of this type.
    const MAXIMUM: Self;

    /// The zero element of this type.
    const ZERO: Self;

    /// The one element of this type.
    const ONE: Self;

    /// Conversion method from `usize` using `as` or an equivalent
    fn from_usize(u: usize) -> Self;

    /// Conversion method from `isize` using `as` or an equivalent
    fn from_isize(i: isize) -> Self;
}

impl SkipfieldType for u16 {
    const MAXIMUM: Self = u16::MAX;
    const ZERO: Self = 0;
    const ONE: Self = 1;

    #[inline(always)]
    fn from_usize(u: usize) -> Self {
        u as u16
    }

    #[inline(always)]
    fn from_isize(i: isize) -> Self {
        i as u16
    }
}

impl SkipfieldType for u8 {
    const MAXIMUM: Self = u8::MAX;
    const ZERO: Self = 0;
    const ONE: Self = 1;

    #[inline(always)]
    fn from_usize(u: usize) -> Self {
        u as u8
    }

    #[inline(always)]
    fn from_isize(i: isize) -> Self {
        i as u8
    }
}