// Vendored from libstd:
// https://github.com/rust-lang/rust/blob/1.57.0/library/core/src/hash/sip.rs
//
// TODO: maybe depend on a hasher from crates.io if this becomes annoying to
// maintain, or change this to a simpler one.
#![cfg(not(feature = "std"))]
use core::cmp;
use core::hash::Hasher;
use core::mem;
use core::ptr;
/// An implementation of SipHash 1-3.
///
/// This is currently the default hashing function used by standard library
/// (e.g., `collections::HashMap` uses it by default).
///
/// See: <https://131002.net/siphash>
pub(crate) struct SipHasher13 {
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(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(
$buf.as_ptr().add($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
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 {
// SAFETY: `i` cannot be greater than `len`, and the caller must guarantee
// that the index start..start+len is in bounds.
out = unsafe { load_int_le!(buf, start + i, u32) } as u64;
i += 4;
}
if i + 1 < len {
// SAFETY: same as above.
out |= (unsafe { load_int_le!(buf, start + i, u16) } as u64) << (i * 8);
i += 2
}
if i < len {
// SAFETY: same as above.
out |= (unsafe { *buf.get_unchecked(start + i) } as u64) << (i * 8);
i += 1;
}
debug_assert_eq!(i, len);
out
}
impl SipHasher13 {
/// Creates a new `SipHasher13` with the two initial keys set to 0.
pub(crate) fn new() -> Self {
Self::new_with_keys(0, 0)
}
/// Creates a `SipHasher13` that is keyed off the provided keys.
fn new_with_keys(key0: u64, key1: u64) -> Self {
let mut state = SipHasher13 {
k0: key0,
k1: key1,
length: 0,
state: State {
v0: 0,
v1: 0,
v2: 0,
v3: 0,
},
tail: 0,
ntail: 0,
};
state.reset();
state
}
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;
}
}
impl Hasher for SipHasher13 {
// Note: no integer hashing methods (`write_u*`, `write_i*`) are defined
// for this type. We could add them, copy the `short_write` implementation
// in librustc_data_structures/sip128.rs, and add `write_u*`/`write_i*`
// methods to `SipHasher`, `SipHasher13`, and `DefaultHasher`. This would
// greatly speed up integer hashing by those hashers, at the cost of
// slightly slowing down compile speeds on some benchmarks. See #69152 for
// details.
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;
// SAFETY: `cmp::min(length, needed)` is guaranteed to not be over `length`
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;
Sip13Rounds::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; // len % 8
let mut i = needed;
while i < len - left {
// SAFETY: because `len - left` is the biggest multiple of 8 under
// `len`, and because `i` starts at `needed` where `len` is `length - needed`,
// `i + 8` is guaranteed to be less than or equal to `length`.
let mi = unsafe { load_int_le!(msg, i, u64) };
self.state.v3 ^= mi;
Sip13Rounds::c_rounds(&mut self.state);
self.state.v0 ^= mi;
i += 8;
}
// SAFETY: `i` is now `needed + len.div_euclid(8) * 8`,
// so `i + left` = `needed + len` = `length`, which is by
// definition equal to `msg.len()`.
self.tail = unsafe { u8to64_le(msg, i, left) };
self.ntail = left;
}
fn finish(&self) -> u64 {
let mut state = self.state;
let b: u64 = ((self.length as u64 & 0xff) << 56) | self.tail;
state.v3 ^= b;
Sip13Rounds::c_rounds(&mut state);
state.v0 ^= b;
state.v2 ^= 0xff;
Sip13Rounds::d_rounds(&mut state);
state.v0 ^ state.v1 ^ state.v2 ^ state.v3
}
}
struct Sip13Rounds;
impl Sip13Rounds {
fn c_rounds(state: &mut State) {
compress!(state);
}
fn d_rounds(state: &mut State) {
compress!(state);
compress!(state);
compress!(state);
}
}
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