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//! # Rot //! Strongly-typed ascii character rotations in the style of Caesar/Rot/Vigenère ciphers. //! This is only meant to be some fun with type-level integers in Rust. //! *Please do not use this as an encryption scheme* as it is *laughably* weak. use typenum::{Integer}; use typenum::consts::{Z0, P26}; use typenum::type_operators::{Same}; use typenum::operator_aliases::{Sum}; use std::marker::PhantomData; use std::ops::{Add, Rem}; use std::fmt; /// A wrapper over Ascii `u8` which rotates alphabetic characters by `N`. /// This is essentially a per-character Caesar cipher with a shift of `N`. /// A collection of this type may also be used to implement a strongly-typed Vigenère cipher. /// An interesting characteristic is that this type can only be converted back to /// a raw `u8` when it has been rotated back into place (i.e `N % 26 == 0`), /// otherwise it is a compile-time type error to do so. /// It is also type-parameterized over the rotation length to prevent /// partial/improper ciphers at compile-time. /// This makes it impossible to use a byte rotated right by 12 when a type contract /// requires a byte rotated left by 13, for example. /// /// # Examples /// ## Rotate some `u8` bytes by 7 positions to the right. /// ``` /// use rot::{Rotate, RotU8}; /// use typenum::consts::P7; /// let s = "a b c"; /// let r : Vec<RotU8<P7>> = s.bytes().rotate_by::<P7>().collect(); /// ``` /// /// ## Try to incorrectly read a rotated byte /// ```compile_fail /// use rot::{Rotate, RotU8}; /// use typenum::consts::P1; /// let c = 'a' as u8; /// let rotated: RotU8<P1> = c.into(); /// let contents: u8 = rotated.into(); // This will fail to type check! /// ``` /// /// ## Perform no-op rotations /// ``` /// use rot::{Rotate, RotU8}; /// use typenum::consts::{Z0, P26}; /// let c = 'a' as u8; /// let rotated_by_zero: RotU8<Z0> = c.into(); /// let rotated_by_26: RotU8<P26> = c.into(); /// let contents_0: u8 = rotated_by_zero.into(); // This works, `c` wasn't rotated. /// assert_eq!(contents_0, 'a' as u8); /// // This works, `c` was rotated back to the start point. /// let contents_26: u8 = rotated_by_26.into(); /// assert_eq!(contents_26, 'a' as u8); /// ``` /// /// ## Type safe signatures /// ``` /// use typenum::{Integer}; /// use typenum::consts::{Z0, P1, N1}; /// use rot::RotU8; /// /// // This function cannot secretly rotate the byte (unless it rotates it back!) /// // This would be useful in a trait definition to enforce a stronger contract. /// fn should_not_rotate<N: Integer>(rc: RotU8<N>) -> RotU8<N> { /// unimplemented!(); /// } /// ``` /// /// ```compile_fail /// use typenum::{Integer}; /// use typenum::consts::{Z0, P1, N1}; /// use rot::RotU8; /// /// fn evil_function<N: Integer>(rc: RotU8<N>) -> RotU8<N> { /// rc.rotate_by::<P1>() // Compile-time error! /// // ^ this has type RotU8<N+1> /// } /// ``` /// /// ``` /// use typenum::{Integer}; /// use typenum::consts::{Z0, P1, N1}; /// use rot::RotU8; /// /// fn not_so_evil_function<N: Integer>(rc: RotU8<N>) -> RotU8<N> { /// rc.rotate_by::<Z0>() // Works fine! Adding zero (or a multiple of 26) doesn't rotate. /// } /// ```` #[derive(Clone, Copy)] pub struct RotU8<N: Integer>(u8, PhantomData<N>); impl<N: Integer> fmt::Display for RotU8<N> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "RotU8<{}>({})", N::to_i8(), self.0 as char) } } impl<N: Integer> fmt::Debug for RotU8<N> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "RotU8<{}>({})", N::to_i8(), &self.0) } } impl<N> RotU8<N> where N: Integer { /// Create a new `RotU8<N>` from a pre-rotated character byte. fn new(rotated: u8) -> Self { Self(rotated, PhantomData) } /// Get the raw underlying `u8` in rotated form. /// ``` /// use typenum::consts::P1; /// use rot::RotU8; /// /// let rotated : RotU8<P1> = ('a' as u8).into(); /// assert_eq!(rotated.as_raw(), 'a' as u8 + 1); /// ``` pub fn as_raw(&self) -> u8 { self.0 } /// Wrap an offset character byte (in the positive _or_ negative directions) /// and ensure it is in the range `[0, 26)` fn wrapping_rotate_mod26(c: i8) -> u8 { ((((c + N::to_i8()) % 26) + 26) % 26) as u8 } /// Rotate a character relative to a start point for a 26 character range. /// If rotating a lowercase ascii letter, the range starts at `'a'`, /// otherwise it starts at `'A'`. fn rotate_relative(c: u8, zero_point: u8) -> u8 { let offset = c - zero_point; Self::wrapping_rotate_mod26(offset as i8) + zero_point } /// Rotate the raw ascii character `ch` `N` positions, /// _if is an alphabetic character_, /// otherwise do not change it. /// If `N` is positive, this performs a wrapped shift to the right. /// If `N` is negative, this performs a wrapped shift to the left. /// A zero value for `N` is identity. /// /// ``` /// use typenum::consts::{N2, P1, Z0}; /// use rot::RotU8; /// /// assert_eq!(Into::<RotU8<P1>>::into('a' as u8).as_raw(), 'b' as u8); /// assert_eq!(Into::<RotU8<N2>>::into('a' as u8).as_raw(), 'y' as u8); /// assert_eq!(Into::<RotU8<Z0>>::into('a' as u8).as_raw(), 'a' as u8); /// assert_eq!(Into::<RotU8<N2>>::into('7' as u8).as_raw(), '7' as u8); /// ``` fn rotate(ch: u8) -> u8 { let c = ch as i8; match ch as char { 'A' ... 'Z' => { Self::rotate_relative(c as u8, 'A' as u8) } 'a' ... 'z' => { Self::rotate_relative(c as u8, 'a' as u8) }, _ => ch } } /// Chain a rotation by `N` with a rotation by `M`. /// ``` /// use typenum::consts::{P1, P2, P3, N1, N4}; /// use rot::RotU8; /// /// let rotate_by_one: RotU8<P1> = ('a' as u8).into(); /// let rotate_by_three: RotU8<P3> = rotate_by_one.rotate_by::<P2>(); /// assert_eq!(rotate_by_three.as_raw(), 'd' as u8); /// let rotate_back: RotU8<N1> = rotate_by_three.rotate_by::<N4>(); /// assert_eq!(rotate_back.as_raw(), 'z' as u8); /// ``` pub fn rotate_by<M>(self) -> RotU8<Sum<M, N>> where M: Add<N> + Integer, <M as Add<N>>::Output: Integer { let c = self.0; let rotated = RotU8::<M>::rotate(c); RotU8::new(rotated) } } impl<N> From<u8> for RotU8<N> where N: Integer { fn from(source: u8) -> Self { let rotated = Self::rotate(source); Self::new(rotated) } } /// Wraps a raw character/byte iterator and rotates each item. pub struct RotIter<N: Integer, I: Iterator> { iter: I, _p: PhantomData<N> } /// Rotate `Self::Item` by `N`. pub trait Rotate where Self: Iterator + Sized { fn rotate_by<N: Integer>(self) -> RotIter<N, Self>; } impl<I> Rotate for I where I: Iterator<Item = u8> { fn rotate_by<N: Integer>(self) -> RotIter<N, Self> { RotIter { iter: self, _p: PhantomData } } } impl<N: Integer, I: Iterator<Item = u8>> Iterator for RotIter<N, I> { type Item = RotU8<N>; fn next(&mut self) -> Option<Self::Item> { self.iter .next() .map(From::from) } } impl<'a, N> Into<u8> for RotU8<N> where N: Rem<P26> + Integer, <N as Rem<P26>>::Output: Integer + Same<Z0>, { fn into(self) -> u8 { self.0 } }