mod.rs

//! Generic hashing support.
//!
//! This module provides a generic way to compute the hash of a value. The
//! simplest way to make a type hashable is to use `#[derive(Hash)]`:
//!
//! # Examples
//!
//! ```rust
//! use std::collections::hash_map::DefaultHasher;
//! use std::hash::{Hash, Hasher};
//!
//! #[derive(Hash)]
//! struct Person {
//!     id: u32,
//!     name: String,
//!     phone: u64,
//! }
//!
//! let person1 = Person {
//!     id: 5,
//!     name: "Janet".to_string(),
//!     phone: 555_666_7777,
//! };
//! let person2 = Person {
//!     id: 5,
//!     name: "Bob".to_string(),
//!     phone: 555_666_7777,
//! };
//!
//! assert!(calculate_hash(&person1) != calculate_hash(&person2));
//!
//! fn calculate_hash<T: Hash>(t: &T) -> u64 {
//!     let mut s = DefaultHasher::new();
//!     t.hash(&mut s);
//!     s.finish()
//! }
//! ```
//!
//! If you need more control over how a value is hashed, you need to implement
//! the [`Hash`] trait:
//!
//! [`Hash`]: trait.Hash.html
//!
//! ```rust
//! use std::collections::hash_map::DefaultHasher;
//! use std::hash::{Hash, Hasher};
//!
//! struct Person {
//!     id: u32,
//!     # #[allow(dead_code)]
//!     name: String,
//!     phone: u64,
//! }
//!
//! impl Hash for Person {
//!     fn hash<H: Hasher>(&self, state: &mut H) {
//!         self.id.hash(state);
//!         self.phone.hash(state);
//!     }
//! }
//!
//! let person1 = Person {
//!     id: 5,
//!     name: "Janet".to_string(),
//!     phone: 555_666_7777,
//! };
//! let person2 = Person {
//!     id: 5,
//!     name: "Bob".to_string(),
//!     phone: 555_666_7777,
//! };
//!
//! assert_eq!(calculate_hash(&person1), calculate_hash(&person2));
//!
//! fn calculate_hash<T: Hash>(t: &T) -> u64 {
//!     let mut s = DefaultHasher::new();
//!     t.hash(&mut s);
//!     s.finish()
//! }
//! ```

#![stable(feature = "rust1", since = "1.0.0")]

use crate::fmt;
use crate::marker;

#[stable(feature = "rust1", since = "1.0.0")]
#[allow(deprecated)]
pub use self::sip::SipHasher;

#[unstable(feature = "hashmap_internals", issue = "0")]
#[allow(deprecated)]
#[doc(hidden)]
pub use self::sip::SipHasher13;

mod sip;

/// A hashable type.
///
/// Types implementing `Hash` are able to be [`hash`]ed with an instance of
/// [`Hasher`].
///
/// ## Implementing `Hash`
///
/// You can derive `Hash` with `#[derive(Hash)]` if all fields implement `Hash`.
/// The resulting hash will be the combination of the values from calling
/// [`hash`] on each field.
///
/// ```
/// #[derive(Hash)]
/// struct Rustacean {
///     name: String,
///     country: String,
/// }
/// ```
///
/// If you need more control over how a value is hashed, you can of course
/// implement the `Hash` trait yourself:
///
/// ```
/// use std::hash::{Hash, Hasher};
///
/// struct Person {
///     id: u32,
///     name: String,
///     phone: u64,
/// }
///
/// impl Hash for Person {
///     fn hash<H: Hasher>(&self, state: &mut H) {
///         self.id.hash(state);
///         self.phone.hash(state);
///     }
/// }
/// ```
///
/// ## `Hash` and `Eq`
///
/// When implementing both `Hash` and [`Eq`], it is important that the following
/// property holds:
///
/// ```text
/// k1 == k2 -> hash(k1) == hash(k2)
/// ```
///
/// In other words, if two keys are equal, their hashes must also be equal.
/// [`HashMap`] and [`HashSet`] both rely on this behavior.
///
/// Thankfully, you won't need to worry about upholding this property when
/// deriving both [`Eq`] and `Hash` with `#[derive(PartialEq, Eq, Hash)]`.
///
/// [`Eq`]: ../../std/cmp/trait.Eq.html
/// [`Hasher`]: trait.Hasher.html
/// [`HashMap`]: ../../std/collections/struct.HashMap.html
/// [`HashSet`]: ../../std/collections/struct.HashSet.html
/// [`hash`]: #tymethod.hash
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Hash {
    /// Feeds this value into the given [`Hasher`].
    ///
    /// # Examples
    ///
    /// ```
    /// use std::collections::hash_map::DefaultHasher;
    /// use std::hash::{Hash, Hasher};
    ///
    /// let mut hasher = DefaultHasher::new();
    /// 7920.hash(&mut hasher);
    /// println!("Hash is {:x}!", hasher.finish());
    /// ```
    ///
    /// [`Hasher`]: trait.Hasher.html
    #[stable(feature = "rust1", since = "1.0.0")]
    fn hash<H: Hasher>(&self, state: &mut H);

    /// Feeds a slice of this type into the given [`Hasher`].
    ///
    /// # Examples
    ///
    /// ```
    /// use std::collections::hash_map::DefaultHasher;
    /// use std::hash::{Hash, Hasher};
    ///
    /// let mut hasher = DefaultHasher::new();
    /// let numbers = [6, 28, 496, 8128];
    /// Hash::hash_slice(&numbers, &mut hasher);
    /// println!("Hash is {:x}!", hasher.finish());
    /// ```
    ///
    /// [`Hasher`]: trait.Hasher.html
    #[stable(feature = "hash_slice", since = "1.3.0")]
    fn hash_slice<H: Hasher>(data: &[Self], state: &mut H)
        where Self: Sized
    {
        for piece in data {
            piece.hash(state);
        }
    }
}

// Separate module to reexport the macro `Hash` from prelude without the trait `Hash`.
pub(crate) mod macros {
    /// Derive macro generating an impl of the trait `Hash`.
    #[rustc_builtin_macro]
    #[rustc_macro_transparency = "semitransparent"]
    #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
    #[allow_internal_unstable(core_intrinsics)]
    pub macro Hash($item:item) { /* compiler built-in */ }
}
#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
#[doc(inline)]
pub use macros::Hash;

/// A trait for hashing an arbitrary stream of bytes.
///
/// Instances of `Hasher` usually represent state that is changed while hashing
/// data.
///
/// `Hasher` provides a fairly basic interface for retrieving the generated hash
/// (with [`finish`]), and writing integers as well as slices of bytes into an
/// instance (with [`write`] and [`write_u8`] etc.). Most of the time, `Hasher`
/// instances are used in conjunction with the [`Hash`] trait.
///
/// # Examples
///
/// ```
/// use std::collections::hash_map::DefaultHasher;
/// use std::hash::Hasher;
///
/// let mut hasher = DefaultHasher::new();
///
/// hasher.write_u32(1989);
/// hasher.write_u8(11);
/// hasher.write_u8(9);
/// hasher.write(b"Huh?");
///
/// println!("Hash is {:x}!", hasher.finish());
/// ```
///
/// [`Hash`]: trait.Hash.html
/// [`finish`]: #tymethod.finish
/// [`write`]: #tymethod.write
/// [`write_u8`]: #method.write_u8
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Hasher {
    /// Returns the hash value for the values written so far.
    ///
    /// Despite its name, the method does not reset the hasher’s internal
    /// state. Additional [`write`]s will continue from the current value.
    /// If you need to start a fresh hash value, you will have to create
    /// a new hasher.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::collections::hash_map::DefaultHasher;
    /// use std::hash::Hasher;
    ///
    /// let mut hasher = DefaultHasher::new();
    /// hasher.write(b"Cool!");
    ///
    /// println!("Hash is {:x}!", hasher.finish());
    /// ```
    ///
    /// [`write`]: #tymethod.write
    #[stable(feature = "rust1", since = "1.0.0")]
    fn finish(&self) -> u64;

    /// Writes some data into this `Hasher`.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::collections::hash_map::DefaultHasher;
    /// use std::hash::Hasher;
    ///
    /// let mut hasher = DefaultHasher::new();
    /// let data = [0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef];
    ///
    /// hasher.write(&data);
    ///
    /// println!("Hash is {:x}!", hasher.finish());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    fn write(&mut self, bytes: &[u8]);

    /// Writes a single `u8` into this hasher.
    #[inline]
    #[stable(feature = "hasher_write", since = "1.3.0")]
    fn write_u8(&mut self, i: u8) {
        self.write(&[i])
    }
    /// Writes a single `u16` into this hasher.
    #[inline]
    #[stable(feature = "hasher_write", since = "1.3.0")]
    fn write_u16(&mut self, i: u16) {
        self.write(&i.to_ne_bytes())
    }
    /// Writes a single `u32` into this hasher.
    #[inline]
    #[stable(feature = "hasher_write", since = "1.3.0")]
    fn write_u32(&mut self, i: u32) {
        self.write(&i.to_ne_bytes())
    }
    /// Writes a single `u64` into this hasher.
    #[inline]
    #[stable(feature = "hasher_write", since = "1.3.0")]
    fn write_u64(&mut self, i: u64) {
        self.write(&i.to_ne_bytes())
    }
    /// Writes a single `u128` into this hasher.
    #[inline]
    #[stable(feature = "i128", since = "1.26.0")]
    fn write_u128(&mut self, i: u128) {
        self.write(&i.to_ne_bytes())
    }
    /// Writes a single `usize` into this hasher.
    #[inline]
    #[stable(feature = "hasher_write", since = "1.3.0")]
    fn write_usize(&mut self, i: usize) {
        self.write(&i.to_ne_bytes())
    }

    /// Writes a single `i8` into this hasher.
    #[inline]
    #[stable(feature = "hasher_write", since = "1.3.0")]
    fn write_i8(&mut self, i: i8) {
        self.write_u8(i as u8)
    }
    /// Writes a single `i16` into this hasher.
    #[inline]
    #[stable(feature = "hasher_write", since = "1.3.0")]
    fn write_i16(&mut self, i: i16) {
        self.write(&i.to_ne_bytes())
    }
    /// Writes a single `i32` into this hasher.
    #[inline]
    #[stable(feature = "hasher_write", since = "1.3.0")]
    fn write_i32(&mut self, i: i32) {
        self.write(&i.to_ne_bytes())
    }
    /// Writes a single `i64` into this hasher.
    #[inline]
    #[stable(feature = "hasher_write", since = "1.3.0")]
    fn write_i64(&mut self, i: i64) {
        self.write(&i.to_ne_bytes())
    }
    /// Writes a single `i128` into this hasher.
    #[inline]
    #[stable(feature = "i128", since = "1.26.0")]
    fn write_i128(&mut self, i: i128) {
        self.write(&i.to_ne_bytes())
    }
    /// Writes a single `isize` into this hasher.
    #[inline]
    #[stable(feature = "hasher_write", since = "1.3.0")]
    fn write_isize(&mut self, i: isize) {
        self.write(&i.to_ne_bytes())
    }
}

#[stable(feature = "indirect_hasher_impl", since = "1.22.0")]
impl<H: Hasher + ?Sized> Hasher for &mut H {
    fn finish(&self) -> u64 {
        (**self).finish()
    }
    fn write(&mut self, bytes: &[u8]) {
        (**self).write(bytes)
    }
    fn write_u8(&mut self, i: u8) {
        (**self).write_u8(i)
    }
    fn write_u16(&mut self, i: u16) {
        (**self).write_u16(i)
    }
    fn write_u32(&mut self, i: u32) {
        (**self).write_u32(i)
    }
    fn write_u64(&mut self, i: u64) {
        (**self).write_u64(i)
    }
    fn write_u128(&mut self, i: u128) {
        (**self).write_u128(i)
    }
    fn write_usize(&mut self, i: usize) {
        (**self).write_usize(i)
    }
    fn write_i8(&mut self, i: i8) {
        (**self).write_i8(i)
    }
    fn write_i16(&mut self, i: i16) {
        (**self).write_i16(i)
    }
    fn write_i32(&mut self, i: i32) {
        (**self).write_i32(i)
    }
    fn write_i64(&mut self, i: i64) {
        (**self).write_i64(i)
    }
    fn write_i128(&mut self, i: i128) {
        (**self).write_i128(i)
    }
    fn write_isize(&mut self, i: isize) {
        (**self).write_isize(i)
    }
}

/// A trait for creating instances of [`Hasher`].
///
/// A `BuildHasher` is typically used (e.g., by [`HashMap`]) to create
/// [`Hasher`]s for each key such that they are hashed independently of one
/// another, since [`Hasher`]s contain state.
///
/// For each instance of `BuildHasher`, the [`Hasher`]s created by
/// [`build_hasher`] should be identical. That is, if the same stream of bytes
/// is fed into each hasher, the same output will also be generated.
///
/// # Examples
///
/// ```
/// use std::collections::hash_map::RandomState;
/// use std::hash::{BuildHasher, Hasher};
///
/// let s = RandomState::new();
/// let mut hasher_1 = s.build_hasher();
/// let mut hasher_2 = s.build_hasher();
///
/// hasher_1.write_u32(8128);
/// hasher_2.write_u32(8128);
///
/// assert_eq!(hasher_1.finish(), hasher_2.finish());
/// ```
///
/// [`build_hasher`]: #tymethod.build_hasher
/// [`Hasher`]: trait.Hasher.html
/// [`HashMap`]: ../../std/collections/struct.HashMap.html
#[stable(since = "1.7.0", feature = "build_hasher")]
pub trait BuildHasher {
    /// Type of the hasher that will be created.
    #[stable(since = "1.7.0", feature = "build_hasher")]
    type Hasher: Hasher;

    /// Creates a new hasher.
    ///
    /// Each call to `build_hasher` on the same instance should produce identical
    /// [`Hasher`]s.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::collections::hash_map::RandomState;
    /// use std::hash::BuildHasher;
    ///
    /// let s = RandomState::new();
    /// let new_s = s.build_hasher();
    /// ```
    ///
    /// [`Hasher`]: trait.Hasher.html
    #[stable(since = "1.7.0", feature = "build_hasher")]
    fn build_hasher(&self) -> Self::Hasher;
}

/// Used to create a default [`BuildHasher`] instance for types that implement
/// [`Hasher`] and [`Default`].
///
/// `BuildHasherDefault<H>` can be used when a type `H` implements [`Hasher`] and
/// [`Default`], and you need a corresponding [`BuildHasher`] instance, but none is
/// defined.
///
/// Any `BuildHasherDefault` is [zero-sized]. It can be created with
/// [`default`][method.Default]. When using `BuildHasherDefault` with [`HashMap`] or
/// [`HashSet`], this doesn't need to be done, since they implement appropriate
/// [`Default`] instances themselves.
///
/// # Examples
///
/// Using `BuildHasherDefault` to specify a custom [`BuildHasher`] for
/// [`HashMap`]:
///
/// ```
/// use std::collections::HashMap;
/// use std::hash::{BuildHasherDefault, Hasher};
///
/// #[derive(Default)]
/// struct MyHasher;
///
/// impl Hasher for MyHasher {
///     fn write(&mut self, bytes: &[u8]) {
///         // Your hashing algorithm goes here!
///        unimplemented!()
///     }
///
///     fn finish(&self) -> u64 {
///         // Your hashing algorithm goes here!
///         unimplemented!()
///     }
/// }
///
/// type MyBuildHasher = BuildHasherDefault<MyHasher>;
///
/// let hash_map = HashMap::<u32, u32, MyBuildHasher>::default();
/// ```
///
/// [`BuildHasher`]: trait.BuildHasher.html
/// [`Default`]: ../default/trait.Default.html
/// [method.default]: #method.default
/// [`Hasher`]: trait.Hasher.html
/// [`HashMap`]: ../../std/collections/struct.HashMap.html
/// [`HashSet`]: ../../std/collections/struct.HashSet.html
/// [zero-sized]: https://doc.rust-lang.org/nomicon/exotic-sizes.html#zero-sized-types-zsts
#[stable(since = "1.7.0", feature = "build_hasher")]
pub struct BuildHasherDefault<H>(marker::PhantomData<H>);

#[stable(since = "1.9.0", feature = "core_impl_debug")]
impl<H> fmt::Debug for BuildHasherDefault<H> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.pad("BuildHasherDefault")
    }
}

#[stable(since = "1.7.0", feature = "build_hasher")]
impl<H: Default + Hasher> BuildHasher for BuildHasherDefault<H> {
    type Hasher = H;

    fn build_hasher(&self) -> H {
        H::default()
    }
}

#[stable(since = "1.7.0", feature = "build_hasher")]
impl<H> Clone for BuildHasherDefault<H> {
    fn clone(&self) -> BuildHasherDefault<H> {
        BuildHasherDefault(marker::PhantomData)
    }
}

#[stable(since = "1.7.0", feature = "build_hasher")]
impl<H> Default for BuildHasherDefault<H> {
    fn default() -> BuildHasherDefault<H> {
        BuildHasherDefault(marker::PhantomData)
    }
}

#[stable(since = "1.29.0", feature = "build_hasher_eq")]
impl<H> PartialEq for BuildHasherDefault<H> {
    fn eq(&self, _other: &BuildHasherDefault<H>) -> bool {
        true
    }
}

#[stable(since = "1.29.0", feature = "build_hasher_eq")]
impl<H> Eq for BuildHasherDefault<H> {}

mod impls {
    use crate::mem;
    use crate::slice;

    use super::*;

    macro_rules! impl_write {
        ($(($ty:ident, $meth:ident),)*) => {$(
            #[stable(feature = "rust1", since = "1.0.0")]
            impl Hash for $ty {
                fn hash<H: Hasher>(&self, state: &mut H) {
                    state.$meth(*self)
                }

                fn hash_slice<H: Hasher>(data: &[$ty], state: &mut H) {
                    let newlen = data.len() * mem::size_of::<$ty>();
                    let ptr = data.as_ptr() as *const u8;
                    state.write(unsafe { slice::from_raw_parts(ptr, newlen) })
                }
            }
        )*}
    }

    impl_write! {
        (u8, write_u8),
        (u16, write_u16),
        (u32, write_u32),
        (u64, write_u64),
        (usize, write_usize),
        (i8, write_i8),
        (i16, write_i16),
        (i32, write_i32),
        (i64, write_i64),
        (isize, write_isize),
        (u128, write_u128),
        (i128, write_i128),
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl Hash for bool {
        fn hash<H: Hasher>(&self, state: &mut H) {
            state.write_u8(*self as u8)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl Hash for char {
        fn hash<H: Hasher>(&self, state: &mut H) {
            state.write_u32(*self as u32)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl Hash for str {
        fn hash<H: Hasher>(&self, state: &mut H) {
            state.write(self.as_bytes());
            state.write_u8(0xff)
        }
    }

    #[stable(feature = "never_hash", since = "1.29.0")]
    impl Hash for ! {
        fn hash<H: Hasher>(&self, _: &mut H) {
            *self
        }
    }

    macro_rules! impl_hash_tuple {
        () => (
            #[stable(feature = "rust1", since = "1.0.0")]
            impl Hash for () {
                fn hash<H: Hasher>(&self, _state: &mut H) {}
            }
        );

        ( $($name:ident)+) => (
            #[stable(feature = "rust1", since = "1.0.0")]
            impl<$($name: Hash),+> Hash for ($($name,)+) where last_type!($($name,)+): ?Sized {
                #[allow(non_snake_case)]
                fn hash<S: Hasher>(&self, state: &mut S) {
                    let ($(ref $name,)+) = *self;
                    $($name.hash(state);)+
                }
            }
        );
    }

    macro_rules! last_type {
        ($a:ident,) => { $a };
        ($a:ident, $($rest_a:ident,)+) => { last_type!($($rest_a,)+) };
    }

    impl_hash_tuple! {}
    impl_hash_tuple! { A }
    impl_hash_tuple! { A B }
    impl_hash_tuple! { A B C }
    impl_hash_tuple! { A B C D }
    impl_hash_tuple! { A B C D E }
    impl_hash_tuple! { A B C D E F }
    impl_hash_tuple! { A B C D E F G }
    impl_hash_tuple! { A B C D E F G H }
    impl_hash_tuple! { A B C D E F G H I }
    impl_hash_tuple! { A B C D E F G H I J }
    impl_hash_tuple! { A B C D E F G H I J K }
    impl_hash_tuple! { A B C D E F G H I J K L }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: Hash> Hash for [T] {
        fn hash<H: Hasher>(&self, state: &mut H) {
            self.len().hash(state);
            Hash::hash_slice(self, state)
        }
    }


    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized + Hash> Hash for &T {
        fn hash<H: Hasher>(&self, state: &mut H) {
            (**self).hash(state);
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized + Hash> Hash for &mut T {
        fn hash<H: Hasher>(&self, state: &mut H) {
            (**self).hash(state);
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Hash for *const T {
        fn hash<H: Hasher>(&self, state: &mut H) {
            if mem::size_of::<Self>() == mem::size_of::<usize>() {
                // Thin pointer
                state.write_usize(*self as *const () as usize);
            } else {
                // Fat pointer
                let (a, b) = unsafe {
                    *(self as *const Self as *const (usize, usize))
                };
                state.write_usize(a);
                state.write_usize(b);
            }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Hash for *mut T {
        fn hash<H: Hasher>(&self, state: &mut H) {
            if mem::size_of::<Self>() == mem::size_of::<usize>() {
                // Thin pointer
                state.write_usize(*self as *const () as usize);
            } else {
                // Fat pointer
                let (a, b) = unsafe {
                    *(self as *const Self as *const (usize, usize))
                };
                state.write_usize(a);
                state.write_usize(b);
            }
        }
    }
}