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/*
* Copyright 2021-2022 taylor.fish <contact@taylor.fish>
*
* This file is part of smallest-uint.
*
* smallest-uint is licensed under the Apache License, Version 2.0
* (the "License"); you may not use smallest-uint except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#![no_std]
#![cfg_attr(test, recursion_limit = "256")]
#![forbid(unsafe_code)]
#![warn(clippy::pedantic)]
#![allow(clippy::default_trait_access)]
#![allow(clippy::module_name_repetitions)]
#![allow(clippy::must_use_candidate)]
//! Given an unsigned [type-level integer][typenum], provides access to
//! the smallest primitive unsigned integer type ([`u8`], [`u16`], etc.) that
//! can represent the integer’s value (or all values less than that value).
//!
//! This is mainly useful for minimizing memory usage when building data
//! structures.
//!
//! This crate depends only on [`core`], so it can be used in `no_std`
//! environments.
//!
//! [`core`]: https://doc.rust-lang.org/core/
//!
//! Example
//! -------
//!
//! ```rust
//! use smallest_uint::{SmallestUIntFor, SmallestUIntUpTo};
//! use std::any::TypeId;
//! use typenum::U65536;
//!
//! assert_eq!(TypeId::of::<SmallestUIntUpTo<U65536>>(), TypeId::of::<u16>());
//! assert_eq!(TypeId::of::<SmallestUIntFor<U65536>>(), TypeId::of::<u32>());
//! ```
//!
//! Crate features
//! --------------
//!
//! If the feature `u128` is enabled, this crate will use the [`u128`] type.
//! This feature is enabled by default.
//!
//! [typenum]: typenum
use num_traits::{NumAssign, PrimInt};
use typenum::Unsigned;
#[cfg(test)]
mod tests;
mod detail {
use super::SmallestUIntFor;
use core::ops::Sub;
use num_traits::{NumAssign, PrimInt};
use typenum::{Len, Max, Unsigned};
use typenum::{Length, Maximum, Sub1};
use typenum::{B1, U1};
type Max1<N> = Maximum<N, U1>;
pub trait GetSmallestUIntFor: Unsigned {
type Type: Default + PrimInt + NumAssign;
}
impl<N> GetSmallestUIntFor for N
where
N: Unsigned + Max<U1>,
Max1<N>: Len,
Length<Max1<N>>: Sub<B1>,
Sub1<Length<Max1<N>>>: Len,
Length<Sub1<Length<Max1<N>>>>: Get,
{
type Type = <Length<Sub1<Length<Max1<N>>>> as Get>::Type;
}
pub trait GetSmallestUIntUpTo: Unsigned {
type Type: Default + PrimInt + NumAssign;
}
impl<N> GetSmallestUIntUpTo for N
where
N: Unsigned + Max<U1>,
Max1<N>: Sub<B1>,
Sub1<Max1<N>>: super::GetSmallestUIntFor,
{
type Type = SmallestUIntFor<Sub1<Max1<N>>>;
}
/// Gets the smallest unsigned integer type with at least 2**`Self` bits.
pub trait Get {
type Type: Default + PrimInt + NumAssign;
}
impl Get for typenum::U0 {
type Type = u8;
}
impl Get for typenum::U1 {
type Type = u8;
}
impl Get for typenum::U2 {
type Type = u8;
}
impl Get for typenum::U3 {
type Type = u8;
}
impl Get for typenum::U4 {
type Type = u16;
}
impl Get for typenum::U5 {
type Type = u32;
}
impl Get for typenum::U6 {
type Type = u64;
}
#[cfg(feature = "u128")]
impl Get for typenum::U7 {
type Type = u128;
}
}
/// Gets the smallest unsigned integer type capable of representing the value
/// of `Self`.
///
/// `Self` is an unsigned [type-level integer](typenum).
///
/// The type is provided as the associated type [`Self::Type`]. If you just
/// want the type and aren’t specifying trait bounds, use the type alias
/// [`SmallestUIntFor`].
pub trait GetSmallestUIntFor: Unsigned + detail::GetSmallestUIntFor {
/// The unsigned integer type.
type Type: Default + PrimInt + NumAssign;
}
/// Alias of [`GetSmallestUIntFor::Type`].
pub type SmallestUIntFor<N> = <N as GetSmallestUIntFor>::Type;
impl<N> GetSmallestUIntFor for N
where
N: detail::GetSmallestUIntFor,
{
type Type = <N as detail::GetSmallestUIntFor>::Type;
}
/// Gets the smallest unsigned integer type capable of representing all values
/// up to, but not including, the value of `Self`.
///
/// `Self` is an unsigned [type-level integer](typenum).
///
/// The type is provided as the associated type [`Self::Type`]. If you just
/// want the type and aren’t specifying trait bounds, use the type alias
/// [`SmallestUIntUpTo`].
pub trait GetSmallestUIntUpTo: Unsigned + detail::GetSmallestUIntUpTo {
/// The unsigned integer type.
type Type: Default + PrimInt + NumAssign;
}
/// Alias of [`GetSmallestUIntUpTo::Type`].
pub type SmallestUIntUpTo<N> = <N as GetSmallestUIntUpTo>::Type;
impl<N> GetSmallestUIntUpTo for N
where
N: detail::GetSmallestUIntUpTo,
{
type Type = <N as detail::GetSmallestUIntUpTo>::Type;
}