//! This is a copy of `core::hash::sip` adapted to providing 128 bit hashes.
use std::cmp;
use std::hash::Hasher;
use std::mem;
use std::ptr;
#[cfg(test)]
mod tests;
#[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 = $v2.rotate_left(32);
}};
}
/// Loads an integer of the desired type from a byte stream, in LE order. Uses
/// `copy_nonoverlapping` to let the compiler generate the most efficient way
/// to load it from a possibly unaligned address.
///
/// Unsafe because: unchecked indexing at i..i+size_of(int_ty)
macro_rules! load_int_le {
($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 {
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;
}
// A specialized write function for values with size <= 8.
//
// The hashing of multi-byte integers depends on endianness. E.g.:
// - little-endian: `write_u32(0xDDCCBBAA)` == `write([0xAA, 0xBB, 0xCC, 0xDD])`
// - big-endian: `write_u32(0xDDCCBBAA)` == `write([0xDD, 0xCC, 0xBB, 0xAA])`
//
// This function does the right thing for little-endian hardware. On
// big-endian hardware `x` must be byte-swapped first to give the right
// behaviour. After any byte-swapping, the input must be zero-extended to
// 64-bits. The caller is responsible for the byte-swapping and
// zero-extension.
#[inline]
fn short_write<T>(&mut self, _x: T, x: u64) {
let size = mem::size_of::<T>();
self.length += size;
// The original number must be zero-extended, not sign-extended.
debug_assert!(if size < 8 { x >> (8 * size) == 0 } else { true });
// The number of bytes needed to fill `self.tail`.
let needed = 8 - self.ntail;
// SipHash parses the input stream as 8-byte little-endian integers.
// Inputs are put into `self.tail` until 8 bytes of data have been
// collected, and then that word is processed.
//
// For example, imagine that `self.tail` is 0x0000_00EE_DDCC_BBAA,
// `self.ntail` is 5 (because 5 bytes have been put into `self.tail`),
// and `needed` is therefore 3.
//
// - Scenario 1, `self.write_u8(0xFF)`: we have already zero-extended
// the input to 0x0000_0000_0000_00FF. We now left-shift it five
// bytes, giving 0x0000_FF00_0000_0000. We then bitwise-OR that value
// into `self.tail`, resulting in 0x0000_FFEE_DDCC_BBAA.
// (Zero-extension of the original input is critical in this scenario
// because we don't want the high two bytes of `self.tail` to be
// touched by the bitwise-OR.) `self.tail` is not yet full, so we
// return early, after updating `self.ntail` to 6.
//
// - Scenario 2, `self.write_u32(0xIIHH_GGFF)`: we have already
// zero-extended the input to 0x0000_0000_IIHH_GGFF. We now
// left-shift it five bytes, giving 0xHHGG_FF00_0000_0000. We then
// bitwise-OR that value into `self.tail`, resulting in
// 0xHHGG_FFEE_DDCC_BBAA. `self.tail` is now full, and we can use it
// to update `self.state`. (As mentioned above, this assumes a
// little-endian machine; on a big-endian machine we would have
// byte-swapped 0xIIHH_GGFF in the caller, giving 0xFFGG_HHII, and we
// would then end up bitwise-ORing 0xGGHH_II00_0000_0000 into
// `self.tail`).
//
self.tail |= x << (8 * self.ntail);
if size < needed {
self.ntail += size;
return;
}
// `self.tail` is full, process it.
self.state.v3 ^= self.tail;
Sip24Rounds::c_rounds(&mut self.state);
self.state.v0 ^= self.tail;
// Continuing scenario 2: we have one byte left over from the input. We
// set `self.ntail` to 1 and `self.tail` to `0x0000_0000_IIHH_GGFF >>
// 8*3`, which is 0x0000_0000_0000_00II. (Or on a big-endian machine
// the prior byte-swapping would leave us with 0x0000_0000_0000_00FF.)
//
// The `if` is needed to avoid shifting by 64 bits, which Rust
// complains about.
self.ntail = size - needed;
self.tail = if needed < 8 { x >> (8 * needed) } else { 0 };
}
#[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(i, i as u64);
}
#[inline]
fn write_u16(&mut self, i: u16) {
self.short_write(i, i.to_le() as u64);
}
#[inline]
fn write_u32(&mut self, i: u32) {
self.short_write(i, i.to_le() as u64);
}
#[inline]
fn write_u64(&mut self, i: u64) {
self.short_write(i, i.to_le() as u64);
}
#[inline]
fn write_usize(&mut self, i: usize) {
self.short_write(i, i.to_le() as u64);
}
#[inline]
fn write_i8(&mut self, i: i8) {
self.short_write(i, i as u8 as u64);
}
#[inline]
fn write_i16(&mut self, i: i16) {
self.short_write(i, (i as u16).to_le() as u64);
}
#[inline]
fn write_i32(&mut self, i: i32) {
self.short_write(i, (i as u32).to_le() as u64);
}
#[inline]
fn write_i64(&mut self, i: i64) {
self.short_write(i, (i as u64).to_le() as u64);
}
#[inline]
fn write_isize(&mut self, i: isize) {
self.short_write(i, (i as usize).to_le() as u64);
}
#[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);
}
}