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    // Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! An implementation of SipHash.

    use prelude::v1::*;

    use marker::PhantomData;
    use ptr;

    /// An implementation of SipHash 1-3.
    ///
    /// See: https://131002.net/siphash/
    #[unstable(feature = "sip_hash_13", issue = "34767")]
    #[derive(Debug, Clone, Default)]
    pub struct SipHasher13 {
        hasher: Hasher<Sip13Rounds>,
    }

    /// An implementation of SipHash 2-4.
    ///
    /// See: https://131002.net/siphash/
    #[unstable(feature = "sip_hash_13", issue = "34767")]
    #[derive(Debug, Clone, Default)]
    pub struct SipHasher24 {
        hasher: Hasher<Sip24Rounds>,
    }

    /// An implementation of SipHash 2-4.
    ///
    /// See: https://131002.net/siphash/
    ///
    /// This is currently the default hashing function used by standard library
    /// (eg. `collections::HashMap` uses it by default).
    ///
    /// 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")]
    #[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)]
    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,
    }

    // sadly, these macro definitions can't appear later,
    // because they're needed in the following defs;
    // this design could be improved.

    macro_rules! u8to64_le {
        ($buf:expr, $i:expr) =>
        ($buf[0+$i] as u64 |
         ($buf[1+$i] as u64) << 8 |
         ($buf[2+$i] as u64) << 16 |
         ($buf[3+$i] as u64) << 24 |
         ($buf[4+$i] as u64) << 32 |
         ($buf[5+$i] as u64) << 40 |
         ($buf[6+$i] as u64) << 48 |
         ($buf[7+$i] as u64) << 56);
        ($buf:expr, $i:expr, $len:expr) =>
        ({
            let mut t = 0;
            let mut out = 0;
            while t < $len {
                out |= ($buf[t+$i] as u64) << t*8;
                t += 1;
            }
            out
        });
    }

    /// Load a full u64 word from a byte stream, in LE order. Use
    /// `copy_nonoverlapping` to let the compiler generate the most efficient way
    /// to load u64 from a possibly unaligned address.
    ///
    /// Unsafe because: unchecked indexing at i..i+8
    #[inline]
    unsafe fn load_u64_le(buf: &[u8], i: usize) -> u64 {
        debug_assert!(i + 8 <= buf.len());
        let mut data = 0u64;
        ptr::copy_nonoverlapping(buf.get_unchecked(i), &mut data as *mut _ as *mut u8, 8);
        data.to_le()
    }

    macro_rules! rotl {
        ($x:expr, $b:expr) =>
        (($x << $b) | ($x >> (64_i32.wrapping_sub($b))))
    }

    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); $v1 = rotl!($v1, 13); $v1 ^= $v0;
            $v0 = rotl!($v0, 32);
            $v2 = $v2.wrapping_add($v3); $v3 = rotl!($v3, 16); $v3 ^= $v2;
            $v0 = $v0.wrapping_add($v3); $v3 = rotl!($v3, 21); $v3 ^= $v0;
            $v2 = $v2.wrapping_add($v1); $v1 = rotl!($v1, 17); $v1 ^= $v2;
            $v2 = rotl!($v2, 32);
        });
    }

    impl SipHasher {
        /// Creates a new `SipHasher` with the two initial keys set to 0.
        #[inline]
        #[stable(feature = "rust1", since = "1.0.0")]
        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")]
        pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher {
            SipHasher(SipHasher24::new_with_keys(key0, key1))
        }
    }

    impl SipHasher13 {
        /// Creates a new `SipHasher13` with the two initial keys set to 0.
        #[inline]
        #[unstable(feature = "sip_hash_13", issue = "34767")]
        pub fn new() -> SipHasher13 {
            SipHasher13::new_with_keys(0, 0)
        }

        /// Creates a `SipHasher13` that is keyed off the provided keys.
        #[inline]
        #[unstable(feature = "sip_hash_13", issue = "34767")]
        pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher13 {
            SipHasher13 {
                hasher: Hasher::new_with_keys(key0, key1)
            }
        }
    }

    impl SipHasher24 {
        /// Creates a new `SipHasher24` with the two initial keys set to 0.
        #[inline]
        #[unstable(feature = "sip_hash_13", issue = "34767")]
        pub fn new() -> SipHasher24 {
            SipHasher24::new_with_keys(0, 0)
        }

        /// Creates a `SipHasher24` that is keyed off the provided keys.
        #[inline]
        #[unstable(feature = "sip_hash_13", issue = "34767")]
        pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher24 {
            SipHasher24 {
                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.write(msg)
        }

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

    #[unstable(feature = "sip_hash_13", issue = "34767")]
    impl super::Hasher for SipHasher13 {
        #[inline]
        fn write(&mut self, msg: &[u8]) {
            self.hasher.write(msg)
        }

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

    #[unstable(feature = "sip_hash_13", issue = "34767")]
    impl super::Hasher for SipHasher24 {
        #[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> {
        #[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;
                if length < needed {
                    self.tail |= u8to64_le!(msg, 0, length) << 8 * self.ntail;
                    self.ntail += length;
                    return
                }

                let m = self.tail | u8to64_le!(msg, 0, needed) << 8 * self.ntail;

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

                self.ntail = 0;
            }

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

            let mut i = needed;
            while i < len - left {
                let mi = unsafe { load_u64_le(msg, i) };

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

                i += 8;
            }

            self.tail = 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> {
        #[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);
        }
    }

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