sip.rs

use std::ptr;

use ::traits::{HashContext, HashFunction};

pub struct SipHashFunction {
    k0: u64,
    k1: u64,
}

impl SipHashFunction {
    #[inline]
    pub fn new() -> SipHashFunction {
        SipHashFunction::new_with_keys(0, 0)
    }

    #[inline]
    pub fn new_with_keys(k0: u64, k1: u64) -> SipHashFunction {
        SipHashFunction {
            k0: k0,
            k1: k1,
        }
    }
}

pub struct SipContext {
    length: usize, // how many bytes we've processed
    v0: u64,      // hash state
    v2: u64,
    v1: u64,
    v3: u64,
    tail: u64, // unprocessed bytes le
    ntail: usize,  // how many bytes in tail are valid
}

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 HashContext for SipContext {
    type Result = u64;

    #[inline(always)]
    fn update(&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(always)]
    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
    }
}

impl HashFunction for SipHashFunction {
    type Context = SipContext;
    
    #[inline(always)]
    fn init(&self) -> SipContext {
        SipContext {
            v0: self.k0 ^ 0x736f6d6570736575,
            v1: self.k1 ^ 0x646f72616e646f6d,
            v2: self.k0 ^ 0x6c7967656e657261,
            v3: self.k1 ^ 0x7465646279746573,
            length: 0,
            tail: 0,
            ntail: 0,
        }
    }
}