sip128.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.

//! This is a copy of `core::hash::sip` adapted to providing 128 bit hashes.

use std::cmp;
use std::hash::Hasher;
use std::slice;
use std::ptr;
use std::mem;

#[derive(Debug, Clone)]
pub struct SipHasher128 {
    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
}

#[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);
    });
}

/// Load 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()
    });
}

/// Load an u64 using up to 7 bytes of a byte slice.
///
/// 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 {
        out = load_int_le!(buf, start + i, u32) as u64;
        i += 4;
    }
    if i + 1 < len {
        out |= (load_int_le!(buf, start + i, u16) as u64) << (i * 8);
        i += 2
    }
    if i < len {
        out |= (*buf.get_unchecked(start + i) as u64) << (i * 8);
        i += 1;
    }
    debug_assert_eq!(i, len);
    out
}


impl SipHasher128 {
    #[inline]
    pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher128 {
        let mut state = SipHasher128 {
            k0: key0,
            k1: key1,
            length: 0,
            state: State {
                v0: 0,
                v1: 0,
                v2: 0,
                v3: 0,
            },
            tail: 0,
            ntail: 0,
        };
        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;

        // This is only done in the 128 bit version:
        self.state.v1 ^= 0xee;
    }

    // Specialized write function that is only valid for buffers with len <= 8.
    // It's used to force inlining of write_u8 and write_usize, those would normally be inlined
    // except for composite types (that includes slices and str hashing because of delimiter).
    // Without this extra push the compiler is very reluctant to inline delimiter writes,
    // degrading performance substantially for the most common use cases.
    #[inline]
    fn short_write(&mut self, msg: &[u8]) {
        debug_assert!(msg.len() <= 8);
        let length = msg.len();
        self.length += length;

        let needed = 8 - self.ntail;
        let fill = cmp::min(length, needed);
        if fill == 8 {
            self.tail = unsafe { load_int_le!(msg, 0, u64) };
        } else {
            self.tail |= unsafe { u8to64_le(msg, 0, fill) } << (8 * self.ntail);
            if length < needed {
                self.ntail += length;
                return;
            }
        }
        self.state.v3 ^= self.tail;
        Sip24Rounds::c_rounds(&mut self.state);
        self.state.v0 ^= self.tail;

        // Buffered tail is now flushed, process new input.
        self.ntail = length - needed;
        self.tail = unsafe { u8to64_le(msg, needed, self.ntail) };
    }

    #[inline(always)]
    fn short_write_gen<T>(&mut self, x: T) {
        let bytes = unsafe {
            slice::from_raw_parts(&x as *const T as *const u8, mem::size_of::<T>())
        };
        self.short_write(bytes);
    }

    #[inline]
    pub fn finish128(mut self) -> (u64, u64) {
        let b: u64 = ((self.length as u64 & 0xff) << 56) | self.tail;

        self.state.v3 ^= b;
        Sip24Rounds::c_rounds(&mut self.state);
        self.state.v0 ^= b;

        self.state.v2 ^= 0xee;
        Sip24Rounds::d_rounds(&mut self.state);
        let _0 = self.state.v0 ^ self.state.v1 ^ self.state.v2 ^ self.state.v3;

        self.state.v1 ^= 0xdd;
        Sip24Rounds::d_rounds(&mut self.state);
        let _1 = self.state.v0 ^ self.state.v1 ^ self.state.v2 ^ self.state.v3;
        (_0, _1)
    }
}

impl Hasher for SipHasher128 {
    #[inline]
    fn write_u8(&mut self, i: u8) {
        self.short_write_gen(i);
    }

    #[inline]
    fn write_u16(&mut self, i: u16) {
        self.short_write_gen(i);
    }

    #[inline]
    fn write_u32(&mut self, i: u32) {
        self.short_write_gen(i);
    }

    #[inline]
    fn write_u64(&mut self, i: u64) {
        self.short_write_gen(i);
    }

    #[inline]
    fn write_usize(&mut self, i: usize) {
        self.short_write_gen(i);
    }

    #[inline]
    fn write_i8(&mut self, i: i8) {
        self.short_write_gen(i);
    }

    #[inline]
    fn write_i16(&mut self, i: i16) {
        self.short_write_gen(i);
    }

    #[inline]
    fn write_i32(&mut self, i: i32) {
        self.short_write_gen(i);
    }

    #[inline]
    fn write_i64(&mut self, i: i64) {
        self.short_write_gen(i);
    }

    #[inline]
    fn write_isize(&mut self, i: isize) {
        self.short_write_gen(i);
    }

    #[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;
            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;
                Sip24Rounds::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;

        let mut i = needed;
        while i < len - left {
            let mi = unsafe { load_int_le!(msg, i, u64) };

            self.state.v3 ^= mi;
            Sip24Rounds::c_rounds(&mut self.state);
            self.state.v0 ^= mi;

            i += 8;
        }

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

    fn finish(&self) -> u64 {
        panic!("SipHasher128 cannot provide valid 64 bit hashes")
    }
}

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

impl 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);
    }
}

#[cfg(test)]
mod test {
    use std::hash::{Hash, Hasher};
    use std::{slice, mem};
    use super::SipHasher128;

    // Hash just the bytes of the slice, without length prefix
    struct Bytes<'a>(&'a [u8]);

    impl<'a> Hash for Bytes<'a> {
        #[allow(unused_must_use)]
        fn hash<H: Hasher>(&self, state: &mut H) {
            for byte in self.0 {
                state.write_u8(*byte);
            }
        }
    }

    fn hash_with<T: Hash>(mut st: SipHasher128, x: &T) -> (u64, u64) {
        x.hash(&mut st);
        st.finish128()
    }

    fn hash<T: Hash>(x: &T) -> (u64, u64) {
        hash_with(SipHasher128::new_with_keys(0, 0), x)
    }

    const TEST_VECTOR : [[u8; 16]; 64] = [
        [0xa3,0x81,0x7f,0x04,0xba,0x25,0xa8,0xe6,0x6d,0xf6,0x72,0x14,0xc7,0x55,0x02,0x93],
        [0xda,0x87,0xc1,0xd8,0x6b,0x99,0xaf,0x44,0x34,0x76,0x59,0x11,0x9b,0x22,0xfc,0x45],
        [0x81,0x77,0x22,0x8d,0xa4,0xa4,0x5d,0xc7,0xfc,0xa3,0x8b,0xde,0xf6,0x0a,0xff,0xe4],
        [0x9c,0x70,0xb6,0x0c,0x52,0x67,0xa9,0x4e,0x5f,0x33,0xb6,0xb0,0x29,0x85,0xed,0x51],
        [0xf8,0x81,0x64,0xc1,0x2d,0x9c,0x8f,0xaf,0x7d,0x0f,0x6e,0x7c,0x7b,0xcd,0x55,0x79],
        [0x13,0x68,0x87,0x59,0x80,0x77,0x6f,0x88,0x54,0x52,0x7a,0x07,0x69,0x0e,0x96,0x27],
        [0x14,0xee,0xca,0x33,0x8b,0x20,0x86,0x13,0x48,0x5e,0xa0,0x30,0x8f,0xd7,0xa1,0x5e],
        [0xa1,0xf1,0xeb,0xbe,0xd8,0xdb,0xc1,0x53,0xc0,0xb8,0x4a,0xa6,0x1f,0xf0,0x82,0x39],
        [0x3b,0x62,0xa9,0xba,0x62,0x58,0xf5,0x61,0x0f,0x83,0xe2,0x64,0xf3,0x14,0x97,0xb4],
        [0x26,0x44,0x99,0x06,0x0a,0xd9,0xba,0xab,0xc4,0x7f,0x8b,0x02,0xbb,0x6d,0x71,0xed],
        [0x00,0x11,0x0d,0xc3,0x78,0x14,0x69,0x56,0xc9,0x54,0x47,0xd3,0xf3,0xd0,0xfb,0xba],
        [0x01,0x51,0xc5,0x68,0x38,0x6b,0x66,0x77,0xa2,0xb4,0xdc,0x6f,0x81,0xe5,0xdc,0x18],
        [0xd6,0x26,0xb2,0x66,0x90,0x5e,0xf3,0x58,0x82,0x63,0x4d,0xf6,0x85,0x32,0xc1,0x25],
        [0x98,0x69,0xe2,0x47,0xe9,0xc0,0x8b,0x10,0xd0,0x29,0x93,0x4f,0xc4,0xb9,0x52,0xf7],
        [0x31,0xfc,0xef,0xac,0x66,0xd7,0xde,0x9c,0x7e,0xc7,0x48,0x5f,0xe4,0x49,0x49,0x02],
        [0x54,0x93,0xe9,0x99,0x33,0xb0,0xa8,0x11,0x7e,0x08,0xec,0x0f,0x97,0xcf,0xc3,0xd9],
        [0x6e,0xe2,0xa4,0xca,0x67,0xb0,0x54,0xbb,0xfd,0x33,0x15,0xbf,0x85,0x23,0x05,0x77],
        [0x47,0x3d,0x06,0xe8,0x73,0x8d,0xb8,0x98,0x54,0xc0,0x66,0xc4,0x7a,0xe4,0x77,0x40],
        [0xa4,0x26,0xe5,0xe4,0x23,0xbf,0x48,0x85,0x29,0x4d,0xa4,0x81,0xfe,0xae,0xf7,0x23],
        [0x78,0x01,0x77,0x31,0xcf,0x65,0xfa,0xb0,0x74,0xd5,0x20,0x89,0x52,0x51,0x2e,0xb1],
        [0x9e,0x25,0xfc,0x83,0x3f,0x22,0x90,0x73,0x3e,0x93,0x44,0xa5,0xe8,0x38,0x39,0xeb],
        [0x56,0x8e,0x49,0x5a,0xbe,0x52,0x5a,0x21,0x8a,0x22,0x14,0xcd,0x3e,0x07,0x1d,0x12],
        [0x4a,0x29,0xb5,0x45,0x52,0xd1,0x6b,0x9a,0x46,0x9c,0x10,0x52,0x8e,0xff,0x0a,0xae],
        [0xc9,0xd1,0x84,0xdd,0xd5,0xa9,0xf5,0xe0,0xcf,0x8c,0xe2,0x9a,0x9a,0xbf,0x69,0x1c],
        [0x2d,0xb4,0x79,0xae,0x78,0xbd,0x50,0xd8,0x88,0x2a,0x8a,0x17,0x8a,0x61,0x32,0xad],
        [0x8e,0xce,0x5f,0x04,0x2d,0x5e,0x44,0x7b,0x50,0x51,0xb9,0xea,0xcb,0x8d,0x8f,0x6f],
        [0x9c,0x0b,0x53,0xb4,0xb3,0xc3,0x07,0xe8,0x7e,0xae,0xe0,0x86,0x78,0x14,0x1f,0x66],
        [0xab,0xf2,0x48,0xaf,0x69,0xa6,0xea,0xe4,0xbf,0xd3,0xeb,0x2f,0x12,0x9e,0xeb,0x94],
        [0x06,0x64,0xda,0x16,0x68,0x57,0x4b,0x88,0xb9,0x35,0xf3,0x02,0x73,0x58,0xae,0xf4],
        [0xaa,0x4b,0x9d,0xc4,0xbf,0x33,0x7d,0xe9,0x0c,0xd4,0xfd,0x3c,0x46,0x7c,0x6a,0xb7],
        [0xea,0x5c,0x7f,0x47,0x1f,0xaf,0x6b,0xde,0x2b,0x1a,0xd7,0xd4,0x68,0x6d,0x22,0x87],
        [0x29,0x39,0xb0,0x18,0x32,0x23,0xfa,0xfc,0x17,0x23,0xde,0x4f,0x52,0xc4,0x3d,0x35],
        [0x7c,0x39,0x56,0xca,0x5e,0xea,0xfc,0x3e,0x36,0x3e,0x9d,0x55,0x65,0x46,0xeb,0x68],
        [0x77,0xc6,0x07,0x71,0x46,0xf0,0x1c,0x32,0xb6,0xb6,0x9d,0x5f,0x4e,0xa9,0xff,0xcf],
        [0x37,0xa6,0x98,0x6c,0xb8,0x84,0x7e,0xdf,0x09,0x25,0xf0,0xf1,0x30,0x9b,0x54,0xde],
        [0xa7,0x05,0xf0,0xe6,0x9d,0xa9,0xa8,0xf9,0x07,0x24,0x1a,0x2e,0x92,0x3c,0x8c,0xc8],
        [0x3d,0xc4,0x7d,0x1f,0x29,0xc4,0x48,0x46,0x1e,0x9e,0x76,0xed,0x90,0x4f,0x67,0x11],
        [0x0d,0x62,0xbf,0x01,0xe6,0xfc,0x0e,0x1a,0x0d,0x3c,0x47,0x51,0xc5,0xd3,0x69,0x2b],
        [0x8c,0x03,0x46,0x8b,0xca,0x7c,0x66,0x9e,0xe4,0xfd,0x5e,0x08,0x4b,0xbe,0xe7,0xb5],
        [0x52,0x8a,0x5b,0xb9,0x3b,0xaf,0x2c,0x9c,0x44,0x73,0xcc,0xe5,0xd0,0xd2,0x2b,0xd9],
        [0xdf,0x6a,0x30,0x1e,0x95,0xc9,0x5d,0xad,0x97,0xae,0x0c,0xc8,0xc6,0x91,0x3b,0xd8],
        [0x80,0x11,0x89,0x90,0x2c,0x85,0x7f,0x39,0xe7,0x35,0x91,0x28,0x5e,0x70,0xb6,0xdb],
        [0xe6,0x17,0x34,0x6a,0xc9,0xc2,0x31,0xbb,0x36,0x50,0xae,0x34,0xcc,0xca,0x0c,0x5b],
        [0x27,0xd9,0x34,0x37,0xef,0xb7,0x21,0xaa,0x40,0x18,0x21,0xdc,0xec,0x5a,0xdf,0x89],
        [0x89,0x23,0x7d,0x9d,0xed,0x9c,0x5e,0x78,0xd8,0xb1,0xc9,0xb1,0x66,0xcc,0x73,0x42],
        [0x4a,0x6d,0x80,0x91,0xbf,0x5e,0x7d,0x65,0x11,0x89,0xfa,0x94,0xa2,0x50,0xb1,0x4c],
        [0x0e,0x33,0xf9,0x60,0x55,0xe7,0xae,0x89,0x3f,0xfc,0x0e,0x3d,0xcf,0x49,0x29,0x02],
        [0xe6,0x1c,0x43,0x2b,0x72,0x0b,0x19,0xd1,0x8e,0xc8,0xd8,0x4b,0xdc,0x63,0x15,0x1b],
        [0xf7,0xe5,0xae,0xf5,0x49,0xf7,0x82,0xcf,0x37,0x90,0x55,0xa6,0x08,0x26,0x9b,0x16],
        [0x43,0x8d,0x03,0x0f,0xd0,0xb7,0xa5,0x4f,0xa8,0x37,0xf2,0xad,0x20,0x1a,0x64,0x03],
        [0xa5,0x90,0xd3,0xee,0x4f,0xbf,0x04,0xe3,0x24,0x7e,0x0d,0x27,0xf2,0x86,0x42,0x3f],
        [0x5f,0xe2,0xc1,0xa1,0x72,0xfe,0x93,0xc4,0xb1,0x5c,0xd3,0x7c,0xae,0xf9,0xf5,0x38],
        [0x2c,0x97,0x32,0x5c,0xbd,0x06,0xb3,0x6e,0xb2,0x13,0x3d,0xd0,0x8b,0x3a,0x01,0x7c],
        [0x92,0xc8,0x14,0x22,0x7a,0x6b,0xca,0x94,0x9f,0xf0,0x65,0x9f,0x00,0x2a,0xd3,0x9e],
        [0xdc,0xe8,0x50,0x11,0x0b,0xd8,0x32,0x8c,0xfb,0xd5,0x08,0x41,0xd6,0x91,0x1d,0x87],
        [0x67,0xf1,0x49,0x84,0xc7,0xda,0x79,0x12,0x48,0xe3,0x2b,0xb5,0x92,0x25,0x83,0xda],
        [0x19,0x38,0xf2,0xcf,0x72,0xd5,0x4e,0xe9,0x7e,0x94,0x16,0x6f,0xa9,0x1d,0x2a,0x36],
        [0x74,0x48,0x1e,0x96,0x46,0xed,0x49,0xfe,0x0f,0x62,0x24,0x30,0x16,0x04,0x69,0x8e],
        [0x57,0xfc,0xa5,0xde,0x98,0xa9,0xd6,0xd8,0x00,0x64,0x38,0xd0,0x58,0x3d,0x8a,0x1d],
        [0x9f,0xec,0xde,0x1c,0xef,0xdc,0x1c,0xbe,0xd4,0x76,0x36,0x74,0xd9,0x57,0x53,0x59],
        [0xe3,0x04,0x0c,0x00,0xeb,0x28,0xf1,0x53,0x66,0xca,0x73,0xcb,0xd8,0x72,0xe7,0x40],
        [0x76,0x97,0x00,0x9a,0x6a,0x83,0x1d,0xfe,0xcc,0xa9,0x1c,0x59,0x93,0x67,0x0f,0x7a],
        [0x58,0x53,0x54,0x23,0x21,0xf5,0x67,0xa0,0x05,0xd5,0x47,0xa4,0xf0,0x47,0x59,0xbd],
        [0x51,0x50,0xd1,0x77,0x2f,0x50,0x83,0x4a,0x50,0x3e,0x06,0x9a,0x97,0x3f,0xbd,0x7c],
    ];

    // Test vector from reference implementation
    #[test]
    fn test_siphash_2_4_test_vector() {
        let k0 = 0x_07_06_05_04_03_02_01_00;
        let k1 = 0x_0f_0e_0d_0c_0b_0a_09_08;

        let mut input: Vec<u8> = Vec::new();

        for i in 0 .. 64 {
            let out = hash_with(SipHasher128::new_with_keys(k0, k1),
                                &Bytes(&input[..]));
            let expected = (
                ((TEST_VECTOR[i][0] as u64) <<  0) |
                ((TEST_VECTOR[i][1] as u64) <<  8) |
                ((TEST_VECTOR[i][2] as u64) << 16) |
                ((TEST_VECTOR[i][3] as u64) << 24) |
                ((TEST_VECTOR[i][4] as u64) << 32) |
                ((TEST_VECTOR[i][5] as u64) << 40) |
                ((TEST_VECTOR[i][6] as u64) << 48) |
                ((TEST_VECTOR[i][7] as u64) << 56),

                ((TEST_VECTOR[i][8] as u64) <<  0) |
                ((TEST_VECTOR[i][9] as u64) <<  8) |
                ((TEST_VECTOR[i][10] as u64) << 16) |
                ((TEST_VECTOR[i][11] as u64) << 24) |
                ((TEST_VECTOR[i][12] as u64) << 32) |
                ((TEST_VECTOR[i][13] as u64) << 40) |
                ((TEST_VECTOR[i][14] as u64) << 48) |
                ((TEST_VECTOR[i][15] as u64) << 56),
            );

            assert_eq!(out, expected);
            input.push(i as u8);
        }
    }

    #[test] #[cfg(target_arch = "arm")]
    fn test_hash_usize() {
        let val = 0xdeadbeef_deadbeef_u64;
        assert!(hash(&(val as u64)) != hash(&(val as usize)));
        assert_eq!(hash(&(val as u32)), hash(&(val as usize)));
    }
    #[test] #[cfg(target_arch = "x86_64")]
    fn test_hash_usize() {
        let val = 0xdeadbeef_deadbeef_u64;
        assert_eq!(hash(&(val as u64)), hash(&(val as usize)));
        assert!(hash(&(val as u32)) != hash(&(val as usize)));
    }
    #[test] #[cfg(target_arch = "x86")]
    fn test_hash_usize() {
        let val = 0xdeadbeef_deadbeef_u64;
        assert!(hash(&(val as u64)) != hash(&(val as usize)));
        assert_eq!(hash(&(val as u32)), hash(&(val as usize)));
    }

    #[test]
    fn test_hash_idempotent() {
        let val64 = 0xdeadbeef_deadbeef_u64;
        assert_eq!(hash(&val64), hash(&val64));
        let val32 = 0xdeadbeef_u32;
        assert_eq!(hash(&val32), hash(&val32));
    }

    #[test]
    fn test_hash_no_bytes_dropped_64() {
        let val = 0xdeadbeef_deadbeef_u64;

        assert!(hash(&val) != hash(&zero_byte(val, 0)));
        assert!(hash(&val) != hash(&zero_byte(val, 1)));
        assert!(hash(&val) != hash(&zero_byte(val, 2)));
        assert!(hash(&val) != hash(&zero_byte(val, 3)));
        assert!(hash(&val) != hash(&zero_byte(val, 4)));
        assert!(hash(&val) != hash(&zero_byte(val, 5)));
        assert!(hash(&val) != hash(&zero_byte(val, 6)));
        assert!(hash(&val) != hash(&zero_byte(val, 7)));

        fn zero_byte(val: u64, byte: usize) -> u64 {
            assert!(byte < 8);
            val & !(0xff << (byte * 8))
        }
    }

    #[test]
    fn test_hash_no_bytes_dropped_32() {
        let val = 0xdeadbeef_u32;

        assert!(hash(&val) != hash(&zero_byte(val, 0)));
        assert!(hash(&val) != hash(&zero_byte(val, 1)));
        assert!(hash(&val) != hash(&zero_byte(val, 2)));
        assert!(hash(&val) != hash(&zero_byte(val, 3)));

        fn zero_byte(val: u32, byte: usize) -> u32 {
            assert!(byte < 4);
            val & !(0xff << (byte * 8))
        }
    }

    #[test]
    fn test_hash_no_concat_alias() {
        let s = ("aa", "bb");
        let t = ("aabb", "");
        let u = ("a", "abb");

        assert!(s != t && t != u);
        assert!(hash(&s) != hash(&t) && hash(&s) != hash(&u));

        let u = [1, 0, 0, 0];
        let v = (&u[..1], &u[1..3], &u[3..]);
        let w = (&u[..], &u[4..4], &u[4..4]);

        assert!(v != w);
        assert!(hash(&v) != hash(&w));
    }

    #[test]
    fn test_write_short_works() {
        let test_usize = 0xd0c0b0a0usize;
        let mut h1 = SipHasher128::new_with_keys(0, 0);
        h1.write_usize(test_usize);
        h1.write(b"bytes");
        h1.write(b"string");
        h1.write_u8(0xFFu8);
        h1.write_u8(0x01u8);
        let mut h2 = SipHasher128::new_with_keys(0, 0);
        h2.write(unsafe {
            slice::from_raw_parts(&test_usize as *const _ as *const u8,
                                  mem::size_of::<usize>())
        });
        h2.write(b"bytes");
        h2.write(b"string");
        h2.write(&[0xFFu8, 0x01u8]);
        assert_eq!(h1.finish128(), h2.finish128());
    }

}