sip.rs.html -- source
Description: Source to the Rust file `src/libcore/hash/sip.rs`.
Keywords: rust, rustlang, rust-lang

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    //! An implementation of SipHash.

    #![allow(deprecated)] // the types in this module are deprecated

    use crate::cmp;
    use crate::marker::PhantomData;
    use crate::mem;
    use crate::ptr;

    /// An implementation of SipHash 1-3.
    ///
    /// This is currently the default hashing function used by standard library
    /// (e.g., `collections::HashMap` uses it by default).
    ///
    /// See: <https://131002.net/siphash>
    #[unstable(feature = "hashmap_internals", issue = "none")]
    #[rustc_deprecated(
        since = "1.13.0",
        reason = "use `std::collections::hash_map::DefaultHasher` instead"
    )]
    #[derive(Debug, Clone, Default)]
    #[doc(hidden)]
    pub struct SipHasher13 {
        hasher: Hasher<Sip13Rounds>,
    }

    /// An implementation of SipHash 2-4.
    ///
    /// See: <https://131002.net/siphash/>
    #[unstable(feature = "hashmap_internals", issue = "none")]
    #[rustc_deprecated(
        since = "1.13.0",
        reason = "use `std::collections::hash_map::DefaultHasher` instead"
    )]
    #[derive(Debug, Clone, Default)]
    struct SipHasher24 {
        hasher: Hasher<Sip24Rounds>,
    }

    /// An implementation of SipHash 2-4.
    ///
    /// See: <https://131002.net/siphash/>
    ///
    /// SipHash is a general-purpose hashing function: it runs at a good
    /// speed (competitive with Spooky and City) and permits strong _keyed_
    /// hashing. This lets you key your hashtables from a strong RNG, such as
    /// [`rand::os::OsRng`](https://doc.rust-lang.org/rand/rand/os/struct.OsRng.html).
    ///
    /// Although the SipHash algorithm is considered to be generally strong,
    /// it is not intended for cryptographic purposes. As such, all
    /// cryptographic uses of this implementation are _strongly discouraged_.
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_deprecated(
        since = "1.13.0",
        reason = "use `std::collections::hash_map::DefaultHasher` instead"
    )]
    #[derive(Debug, Clone, Default)]
    pub struct SipHasher(SipHasher24);

    #[derive(Debug)]
    struct Hasher<S: Sip> {
        k0: u64,
        k1: u64,
        length: usize, // how many bytes we've processed
        state: State,  // hash State
        tail: u64,     // unprocessed bytes le
        ntail: usize,  // how many bytes in tail are valid
        _marker: PhantomData<S>,
    }

    #[derive(Debug, Clone, Copy)]
    #[repr(C)]
    struct State {
        // v0, v2 and v1, v3 show up in pairs in the algorithm,
        // and simd implementations of SipHash will use vectors
        // of v02 and v13. By placing them in this order in the struct,
        // the compiler can pick up on just a few simd optimizations by itself.
        v0: u64,
        v2: u64,
        v1: u64,
        v3: u64,
    }

    macro_rules! compress {
        ($state:expr) => {{ compress!($state.v0, $state.v1, $state.v2, $state.v3) }};
        ($v0:expr, $v1:expr, $v2:expr, $v3:expr) => {{
            $v0 = $v0.wrapping_add($v1);
            $v1 = $v1.rotate_left(13);
            $v1 ^= $v0;
            $v0 = $v0.rotate_left(32);
            $v2 = $v2.wrapping_add($v3);
            $v3 = $v3.rotate_left(16);
            $v3 ^= $v2;
            $v0 = $v0.wrapping_add($v3);
            $v3 = $v3.rotate_left(21);
            $v3 ^= $v0;
            $v2 = $v2.wrapping_add($v1);
            $v1 = $v1.rotate_left(17);
            $v1 ^= $v2;
            $v2 = $v2.rotate_left(32);
        }};
    }

    /// Loads an integer of the desired type from a byte stream, in LE order. Uses
    /// `copy_nonoverlapping` to let the compiler generate the most efficient way
    /// to load it from a possibly unaligned address.
    ///
    /// Unsafe because: unchecked indexing at i..i+size_of(int_ty)
    macro_rules! load_int_le {
        ($buf:expr, $i:expr, $int_ty:ident) => {{
            debug_assert!($i + mem::size_of::<$int_ty>() <= $buf.len());
            let mut data = 0 as $int_ty;
            ptr::copy_nonoverlapping(
                $buf.get_unchecked($i),
                &mut data as *mut _ as *mut u8,
                mem::size_of::<$int_ty>(),
            );
            data.to_le()
        }};
    }

    /// Loads a u64 using up to 7 bytes of a byte slice. It looks clumsy but the
    /// `copy_nonoverlapping` calls that occur (via `load_int_le!`) all have fixed
    /// sizes and avoid calling `memcpy`, which is good for speed.
    ///
    /// Unsafe because: unchecked indexing at start..start+len
    #[inline]
    unsafe fn u8to64_le(buf: &[u8], start: usize, len: usize) -> u64 {
        debug_assert!(len < 8);
        let mut i = 0; // current byte index (from LSB) in the output u64
        let mut out = 0;
        if i + 3 < len {
            // SAFETY: `i` cannot be greater than `len`, and the caller must guarantee
            // that the index start..start+len is in bounds.
            out = unsafe { load_int_le!(buf, start + i, u32) } as u64;
            i += 4;
        }
        if i + 1 < len {
            // SAFETY: same as above.
            out |= (unsafe { load_int_le!(buf, start + i, u16) } as u64) << (i * 8);
            i += 2
        }
        if i < len {
            // SAFETY: same as above.
            out |= (unsafe { *buf.get_unchecked(start + i) } as u64) << (i * 8);
            i += 1;
        }
        debug_assert_eq!(i, len);
        out
    }

    impl SipHasher {
        /// Creates a new `SipHasher` with the two initial keys set to 0.
        #[inline]
        #[stable(feature = "rust1", since = "1.0.0")]
        #[rustc_deprecated(
            since = "1.13.0",
            reason = "use `std::collections::hash_map::DefaultHasher` instead"
        )]
        pub fn new() -> SipHasher {
            SipHasher::new_with_keys(0, 0)
        }

        /// Creates a `SipHasher` that is keyed off the provided keys.
        #[inline]
        #[stable(feature = "rust1", since = "1.0.0")]
        #[rustc_deprecated(
            since = "1.13.0",
            reason = "use `std::collections::hash_map::DefaultHasher` instead"
        )]
        pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher {
            SipHasher(SipHasher24 { hasher: Hasher::new_with_keys(key0, key1) })
        }
    }

    impl SipHasher13 {
        /// Creates a new `SipHasher13` with the two initial keys set to 0.
        #[inline]
        #[unstable(feature = "hashmap_internals", issue = "none")]
        #[rustc_deprecated(
            since = "1.13.0",
            reason = "use `std::collections::hash_map::DefaultHasher` instead"
        )]
        pub fn new() -> SipHasher13 {
            SipHasher13::new_with_keys(0, 0)
        }

        /// Creates a `SipHasher13` that is keyed off the provided keys.
        #[inline]
        #[unstable(feature = "hashmap_internals", issue = "none")]
        #[rustc_deprecated(
            since = "1.13.0",
            reason = "use `std::collections::hash_map::DefaultHasher` instead"
        )]
        pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher13 {
            SipHasher13 { hasher: Hasher::new_with_keys(key0, key1) }
        }
    }

    impl<S: Sip> Hasher<S> {
        #[inline]
        fn new_with_keys(key0: u64, key1: u64) -> Hasher<S> {
            let mut state = Hasher {
                k0: key0,
                k1: key1,
                length: 0,
                state: State { v0: 0, v1: 0, v2: 0, v3: 0 },
                tail: 0,
                ntail: 0,
                _marker: PhantomData,
            };
            state.reset();
            state
        }

        #[inline]
        fn reset(&mut self) {
            self.length = 0;
            self.state.v0 = self.k0 ^ 0x736f6d6570736575;
            self.state.v1 = self.k1 ^ 0x646f72616e646f6d;
            self.state.v2 = self.k0 ^ 0x6c7967656e657261;
            self.state.v3 = self.k1 ^ 0x7465646279746573;
            self.ntail = 0;
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl super::Hasher for SipHasher {
        #[inline]
        fn write(&mut self, msg: &[u8]) {
            self.0.hasher.write(msg)
        }

        #[inline]
        fn finish(&self) -> u64 {
            self.0.hasher.finish()
        }
    }

    #[unstable(feature = "hashmap_internals", issue = "none")]
    impl super::Hasher for SipHasher13 {
        #[inline]
        fn write(&mut self, msg: &[u8]) {
            self.hasher.write(msg)
        }

        #[inline]
        fn finish(&self) -> u64 {
            self.hasher.finish()
        }
    }

    impl<S: Sip> super::Hasher for Hasher<S> {
        // Note: no integer hashing methods (`write_u*`, `write_i*`) are defined
        // for this type. We could add them, copy the `short_write` implementation
        // in librustc_data_structures/sip128.rs, and add `write_u*`/`write_i*`
        // methods to `SipHasher`, `SipHasher13`, and `DefaultHasher`. This would
        // greatly speed up integer hashing by those hashers, at the cost of
        // slightly slowing down compile speeds on some benchmarks. See #69152 for
        // details.
        #[inline]
        fn write(&mut self, msg: &[u8]) {
            let length = msg.len();
            self.length += length;

            let mut needed = 0;

            if self.ntail != 0 {
                needed = 8 - self.ntail;
                // SAFETY: `cmp::min(length, needed)` is guaranteed to not be over `length`
                self.tail |= unsafe { u8to64_le(msg, 0, cmp::min(length, needed)) } << (8 * self.ntail);
                if length < needed {
                    self.ntail += length;
                    return;
                } else {
                    self.state.v3 ^= self.tail;
                    S::c_rounds(&mut self.state);
                    self.state.v0 ^= self.tail;
                    self.ntail = 0;
                }
            }

            // Buffered tail is now flushed, process new input.
            let len = length - needed;
            let left = len & 0x7; // len % 8

            let mut i = needed;
            while i < len - left {
                // SAFETY: because `len - left` is the biggest multiple of 8 under
                // `len`, and because `i` starts at `needed` where `len` is `length - needed`,
                // `i + 8` is guaranteed to be less than or equal to `length`.
                let mi = unsafe { load_int_le!(msg, i, u64) };

                self.state.v3 ^= mi;
                S::c_rounds(&mut self.state);
                self.state.v0 ^= mi;

                i += 8;
            }

            // SAFETY: `i` is now `needed + len.div_euclid(8) * 8`,
            // so `i + left` = `needed + len` = `length`, which is by
            // definition equal to `msg.len()`.
            self.tail = unsafe { u8to64_le(msg, i, left) };
            self.ntail = left;
        }

        #[inline]
        fn finish(&self) -> u64 {
            let mut state = self.state;

            let b: u64 = ((self.length as u64 & 0xff) << 56) | self.tail;

            state.v3 ^= b;
            S::c_rounds(&mut state);
            state.v0 ^= b;

            state.v2 ^= 0xff;
            S::d_rounds(&mut state);

            state.v0 ^ state.v1 ^ state.v2 ^ state.v3
        }
    }

    impl<S: Sip> Clone for Hasher<S> {
        #[inline]
        fn clone(&self) -> Hasher<S> {
            Hasher {
                k0: self.k0,
                k1: self.k1,
                length: self.length,
                state: self.state,
                tail: self.tail,
                ntail: self.ntail,
                _marker: self._marker,
            }
        }
    }

    impl<S: Sip> Default for Hasher<S> {
        /// Creates a `Hasher<S>` with the two initial keys set to 0.
        #[inline]
        fn default() -> Hasher<S> {
            Hasher::new_with_keys(0, 0)
        }
    }

    #[doc(hidden)]
    trait Sip {
        fn c_rounds(_: &mut State);
        fn d_rounds(_: &mut State);
    }

    #[derive(Debug, Clone, Default)]
    struct Sip13Rounds;

    impl Sip for Sip13Rounds {
        #[inline]
        fn c_rounds(state: &mut State) {
            compress!(state);
        }

        #[inline]
        fn d_rounds(state: &mut State) {
            compress!(state);
            compress!(state);
            compress!(state);
        }
    }

    #[derive(Debug, Clone, Default)]
    struct Sip24Rounds;

    impl Sip for Sip24Rounds {
        #[inline]
        fn c_rounds(state: &mut State) {
            compress!(state);
            compress!(state);
        }

        #[inline]
        fn d_rounds(state: &mut State) {
            compress!(state);
            compress!(state);
            compress!(state);
            compress!(state);
        }
    }