sip.rs

// 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 2-4.

use prelude::v1::*;

use ptr;
use super::Hasher;

/// 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_.
#[derive(Debug)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct SipHasher {
    k0: u64,
    k1: u64,
    length: usize, // how many bytes we've processed
    // 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, // hash state
    v2: u64,
    v1: u64,
    v3: u64,
    tail: u64, // unprocessed bytes le
    ntail: usize, // how many bytes in tail are valid
}

// 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 {
    ($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 {
        let mut state = SipHasher {
            k0: key0,
            k1: key1,
            length: 0,
            v0: 0,
            v1: 0,
            v2: 0,
            v3: 0,
            tail: 0,
            ntail: 0,
        };
        state.reset();
        state
    }

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

#[stable(feature = "rust1", since = "1.0.0")]
impl Hasher for SipHasher {
    #[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.v3 ^= m;
            compress!(self.v0, self.v1, self.v2, self.v3);
            compress!(self.v0, self.v1, self.v2, self.v3);
            self.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.v3 ^= mi;
            compress!(self.v0, self.v1, self.v2, self.v3);
            compress!(self.v0, self.v1, self.v2, self.v3);
            self.v0 ^= mi;

            i += 8;
        }

        self.tail = u8to64_le!(msg, i, left);
        self.ntail = left;
    }

    #[inline]
    fn finish(&self) -> u64 {
        let mut v0 = self.v0;
        let mut v1 = self.v1;
        let mut v2 = self.v2;
        let mut v3 = self.v3;

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

        v3 ^= b;
        compress!(v0, v1, v2, v3);
        compress!(v0, v1, v2, v3);
        v0 ^= b;

        v2 ^= 0xff;
        compress!(v0, v1, v2, v3);
        compress!(v0, v1, v2, v3);
        compress!(v0, v1, v2, v3);
        compress!(v0, v1, v2, v3);

        v0 ^ v1 ^ v2 ^ v3
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Clone for SipHasher {
    #[inline]
    fn clone(&self) -> SipHasher {
        SipHasher {
            k0: self.k0,
            k1: self.k1,
            length: self.length,
            v0: self.v0,
            v1: self.v1,
            v2: self.v2,
            v3: self.v3,
            tail: self.tail,
            ntail: self.ntail,
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Default for SipHasher {
    fn default() -> SipHasher {
        SipHasher::new()
    }
}